en/subtitles/13. Persistence and Documents.srt

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[MUSIC]                         

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>> Stanford University.         
>> All right, welcome to        

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lecture number 13 Stanford      
CS193P fall of 2017 and         

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18. So we have a very which     
demo today, I've actually kind  

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of compressed it ciz I really   
need to get to the slides,      

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very important topic which      
is persistance. And so          

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let me just dive                
right into that demo,           

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and then we'll get to           
persistence right after that.   

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So the demo here is I'm         
gonna take our emoji art and    

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add a little way to make        
a text field appear             

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up in our little collection     
view that slides around, so     

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we can add more emoji to that   
little sliding thing. So        

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how are we going to do that?    
Well to make this go quicker,   

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here's our emoji as we          
left it off last time. But      

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I've made a couple of little    
changes here. I've added two    

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collection view cells.          
You see them right here,        

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this one with the plus button.  
This is just a UI button,       

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right here and then this one    
has got a UI text field.        

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That's what this little,        

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I don't know if you can see     
the light gray in there, but    

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this is a text                  
field inside here.              

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That's the only thing that's    
in these new cells, and each    

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of these cells, of course,      
I gave it an identifier.        

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This one's called               
an AddEmojiButtonCell,          

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and this one's called           
a EmojiInputCell.               

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This cell is just a standard    
UI collection view cell.        

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So if I look at it right here,  
you can see that its class is   

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just UI collection view cell.   
But this one is a special       

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text field collection view      
cell. A subclass of collection  

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view cell that handles this     
text field a little bit.        

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And so we're gonna go take a    
look at the code from that and  

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actually add a little bit of    
extra code to that, cuz I want  

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to show you just a kind of      
a trickier way to do things.    

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That's not tricky, but it's     
a really valuable way that,     

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that's a little bit advanced,   
so                              

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I wanted to make sure you       
learn that. All right, so       

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I have these two new cells.     
Let's take a look at this code  

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for the text field, collection  
view cell, that is right here,  

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it's a very very simple cell,   
it just has an outlet           

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to that text field              
you saw right there.            

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Now notice when                 
my outlet is set,               

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I immediately set that          
outlet's delegate to my, me,    

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myself. And                     
I'm a UITextFieldDelegate.      

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Okay remember the slides        
from last time. And             

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so I only implemented one       
delegate method here which is   

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textfieldShouldReturn and       
what it does, when you press    

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the return key on               
the keyboard, it resigns first  

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responder, which means it       
stops using the keyboard. And   

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the keyboard disappears. So if  
you don't do this little thing  

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right here, then when you       
press Return on the keyboard,   

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the keyboard stays up. Okay     
and the cursor keeps blinking.  

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Here it caused it to go away.   

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And we're gonna add another     

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delicate method here            
in a second. So now,            

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remember that I have these      
two cells right here, right?    

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The emoji button one and then   
the input cell right there. So  

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now, let's go back to our       
emoji art controller code and   

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look how I dealt with this,     
how I put this in the UI.       

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Well, first of all that         
little plus button,             

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it uses target action to send   
this message to my controller.  

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Now notice it's sending it      
directly to the controller.     

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If I had multiple of            
those plus buttons,             

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they'd all be sending           
this message.                   

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But luckily I only have one     
so, this is perfectly fine.     

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Remember that a lot of times    
if we have something in         

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a collection in                 
bureau table view and           

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it's sending target action,     

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we have it send it to a custom  
cell, right? Because we want    

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each one to receive a special   
thing, but, here we can have    

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things send it through the      
controller. Now all of this     

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that plus button does is that   
it turns this adding emoji on.  

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Because we're in the process    
of addingEmoji after you press  

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that button. And                
then it reloads section zero.   

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Now I have decided that I'm     
gonna put that plus button and  

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the text field name in          
a different section from all    

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the rest. Remember Collection   
Views, like Table Views,        

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they have sections, so          

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I'm gonna have section zero is  
gonna be the plus button or     

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the text field, depending on    
whether I'm addingEmoji at      

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the time and then section       
one is gonna be all mine.       

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Emoji as I'm used to it today.  
So how do we implement that?    

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Well, we have to say we         
have two sections now,          

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instead of just one section.    
And when we get the number      

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of items in a section here,     

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we have to look at the section  
and see if it's section 0,      

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then we have 1, either the      
plus button or the text field,  

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or we have the number of        
emojis if it's our old,         

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the old thing we used to have   
where it's all those emojis     

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going across. Then we have to   
change our cell for item at.    

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This is the thing that gets     
a cell for a given thing.       

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So look at this                 
section as well. So             

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this is what this code used to  
look like and I just put it in  

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an if the section is one then   
do what we were doing before.   

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Otherwise if the section        
is zero, then if I'm adding     

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emoji, I'm gonna put that       
text field in there. And        

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if i'm not adding emoji, I'm    
gonna put the button in there.  

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the text field are going to     
be exchanging places right?     

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So the button and               

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You press the button,           
it's going to change and        

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switch to the text field        
because I'm gonna set this      

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adding emoji to true and then   
I'm gonna reload my section.    

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And that's gonna cause all of   
this to get called again and    

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it's gonna switch back and      
forth. So I'm gonna have to     

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put some code in here, when     
I switch to the text field      

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to get the text out, and we're  
gonna talk about that. But      

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before that, let me show you    
a couple other things I did.    

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One is I want the text field,   
when it's there, to be very     

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wide. I don't want it to be     
tiny like all the other cells.  

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I want it to be a wide cell,    
so                              

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I overrode this method here. A  
collection view layout method   

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called size for                 
item at index path.             

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And you return a size for       
an item at that path. Well,     

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if I'm adding emoji and we're   
talking about section zero,     

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then I'm going for              
wide buttons, otherwise,        

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I'm doing the standard size     
I had before, and yes,          

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these are blue numbers, they    
shouldn't be here. I should be  

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calculating this based on the   
size of the font that the user  

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chose and the accessibility     
slider, all that, but we don't  

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have time for all that so I'm   
using blue numbers here. And    

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then another one I overrode     
here is will display cell.      

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That's another cool             
little delegate method          

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in collection view.             

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This is called right            
before it displays a cell.      

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And here what I do is if I'm    
displaying the input cell,      

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that little text field one,     
I make it become the first      

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responder. That way when        
the text field comes up,        

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the keyboard comes up.          
See why I'm doing that? So      

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will display cell. Another      
fun collection do you think?    

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I only had to do another        
couple other small things.      

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I disabled dragging here        
if we're editing the emoji.     

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If we're typing a new emoji, I  
don't let the dragging happen   

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because it just                 
messes things up                

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to try to be swapping things    
around at the same time.        

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That we're adding stuff, so     
I took that out of there.       

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I also don't allow dropping,    
where's my drop code here?      

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DropProposal, where is that?    
I can't find any in here,       

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here it is. So I don't allow    
when you're, repositioning      

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the collection items,           
right, the little emojis.       

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I don't allow putting it        
into section 0. That's where    

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the plus button is. I don't     
wanna drop smiley face for      

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the bike into where the plus    
button is, that section. So     

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I just say here that            
if the index path               

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is section one, then I'll do    
this thing where I'll copy or   

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move the emoji. Otherwise, I'm  
gonna say the drop proposal is  

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cancelled, which means I        
can't drop there. Everyone      

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cool with that? So that's all   
the code that I did. Now,       

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the last thing, let's run and   
see what this looks like here.  

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Here's our UI. So, here's our   
thing that we have so I can     

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move things around. There's     
the plus button on the left.    

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Oops. If I press that plus      
button, you see it gets         

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replaced with the text field.   
And I can bring up my           

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keyboard here and start typing  
in, some, I don't know,         

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what do we got here some        
shoes and hats and stuff.       

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And typing these things in.     
Now if I press the return key,  

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my keyboard is gonna go away    
cuz I implemented that one      

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text delegate method.           
see how it went away? But it's  

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not adding the emoji, because   
I have not put any code         

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in here that actually takes     
what I typed in there. And      

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adds it to my scrolling list.   
So how am I gonna do that?      

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Well that is the trick.         
Let's go take a look.           

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And we want to essentially,     
in our text field right here,   

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when the text field resigns     
being first responder, right,   

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when it stops showing           
the text field. Then we want    

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to put that in. So of course,   
we're gonna use this            

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delegate method I talked about  
called TextFieldDidEndEditing.  

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Editing, editing. There it is.  
And when this happens,          

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I wanna talk back to my         
collection view basically and   

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say add the emoji that          
was in my text field. But       

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how do I talk back to my        
collection view here?           

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The collection view cells       
don't really have a pointer to  

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their collection view.          

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So, it's an interesting         
problem to solve, and           

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I'm actually gonna solve it.    
A lot of people would solve it  

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by trying to go find            
the collection here and         

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talk to it or                   
something like that. But        

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an actually a much easier way   
to do this with closures. So    

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I'm create a var, public var    
in the cell called resignation  

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handler. And it's just going    
to be a closure, a function     

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that takes no arguments and     
returns no arguments.           

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In fact I'm even going to make  
this an optional function so    

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that it can be nill,            
doesn't have to be set.         

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And when text field editing     
happens I'm just gonna          

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call this thing, resignation    
handler. Might be nil so        

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I'll optional chain it and      
call it. So I'm just calling    

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that function. Now, anyone who  
is interested, when my text     

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fields resigns can just set     
this closure to something. And  

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that's exactly what             
we're gonna do back here        

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in our controller.              
Where we load up our cell,      

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which is right here. If we're   
doing the emoji input cell,     

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which is the thing              
with the text fill.             

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I'm just gonna say if I can     
let input cell equal this cell  

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as a text field collection      
cell, which is collection view  

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cell which is that cell that    
has that text field in it.      

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Then I'm gonna set the input    
cells, resignation handler,     

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resignation handler.            
Now, I'm just going to set it   

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to be some closure that does    
what I want when that text      

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field resigns to the first      
responder. Well, what do I      

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want to do? I want to take      
the emoji out of it and         

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put into my list, of course.    
So, let's just do that.         

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I'm gonna set my, well, first,  
I'm going to say, if I can let  

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text equal the input cells      
text fields text, so            

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if you can get some             
text out of there.              

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Then I am just going            
to have my emojis,              

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remember that's my model right  
here? That's the thing that,    

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oops, where is it?              
Shows all the emojis here,      

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I'm just going to add to that   
thing I'm just gonna say my     

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emojis equals, that text        
that was in the text field.     

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And I'm gonna map them, all     
the characters in there to be   

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strings, so that I have an      
array of strings, right? And    

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I'm gonna add that to           
what's already there.           

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So that's emojis just are the   
emojis we already have. And     

212
00:10:30,396 --> 00:10:32,062
I'm even going to do a little   
trick where I'm going to        

213
00:10:32,131 --> 00:10:36,133
uniquify them, uniquified.      
This is just a little thing     

214
00:10:36,202 --> 00:10:38,703
that I put in that utilities    
thing which takes an array and  

215
00:10:38,772 --> 00:10:40,671
makes sure all                  
the items are unique.           

216
00:10:40,740 --> 00:10:43,040
Because I don't want to         
have multiple smiley faces,     

217
00:10:43,109 --> 00:10:46,877
multiple bikes, whatever. Now   
of course I get this of, hey    

218
00:10:46,946 --> 00:10:50,682
you are using self implicitly   
here, you should put self dot.  

219
00:10:50,750 --> 00:10:53,718
And every time you do that,     
you're gonna pause and          

220
00:10:53,787 --> 00:10:56,287
say hmm, does this              
create a memory cycle or        

221
00:10:56,356 --> 00:10:59,223
is this perhaps causing         
a multithreaded issue?          

222
00:10:59,292 --> 00:11:01,426
Well there's no multi           
threading issue problem here.   

223
00:11:01,494 --> 00:11:04,261
Cuz we we don't have a problem  
with cells being scrolled       

224
00:11:04,330 --> 00:11:07,431
off and scrolled back on like   
you have in your homework. But  

225
00:11:07,500 --> 00:11:11,202
there is a memory cycle here.   
You see how                     

226
00:11:11,271 --> 00:11:13,704
there's a memory cycle because  
self is the collection,         

227
00:11:13,773 --> 00:11:14,639
is our selfish                  
view-controller.                

228
00:11:14,708 --> 00:11:16,640
And we point to our             
collection view.                

229
00:11:16,709 --> 00:11:20,111
Our collection view points to   
its cells, of course. Its cell  

230
00:11:20,180 --> 00:11:23,648
points to this closure.         
And this closure points back    

231
00:11:23,717 --> 00:11:26,651
to ourself. So it's going       
around and round. So            

232
00:11:26,720 --> 00:11:30,455
we have to break this           
with weak self. And             

233
00:11:30,524 --> 00:11:33,824
then make all our selfs         
here be question mark.          

234
00:11:33,893 --> 00:11:37,495
This is a self also. It can be  
self exclamation point because  

235
00:11:37,563 --> 00:11:40,231
we won't get there if this      
is nil. So, that's good,        

236
00:11:40,300 --> 00:11:42,466
but there's actually            
another one in here.            

237
00:11:42,535 --> 00:11:44,869
Sometimes, just because         
it tells you about self,        

238
00:11:44,938 --> 00:11:46,704
doesn't mean there might        
not be other ones in there.     

239
00:11:46,773 --> 00:11:50,441
And there is another one, it's  
this. This var is the input     

240
00:11:50,510 --> 00:11:52,877
cell and I'm using it           
inside this closure,            

241
00:11:52,945 --> 00:11:55,546
which will capture it.          
And yet it is pointing          

242
00:11:55,615 --> 00:11:59,117
back to the closure through     
its resignation handler,        

243
00:11:59,185 --> 00:12:01,552
so this has to be               
broken as well.                 

244
00:12:01,621 --> 00:12:06,857
Now this one we can broke,      
break, with unowned because     

245
00:12:06,926 --> 00:12:10,995
we know we would never be in    
this closure executing it,      

246
00:12:11,063 --> 00:12:15,165
if this were nil. Because by    
definition, we're executing     

247
00:12:15,234 --> 00:12:18,603
its resignationHandler, so we   
can use unowned, in this case,  

248
00:12:18,671 --> 00:12:21,973
to do that. And what else do    
we need to do here? Well, we    

249
00:12:22,042 --> 00:12:25,376
just need to stop saying that   
we are adding emoji, because    

250
00:12:25,445 --> 00:12:28,612
we're not, right, we've         
finished adding emoji here.     

251
00:12:28,681 --> 00:12:32,917
And then, we're gonna have to   
ask our emoji collection view   

252
00:12:32,986 --> 00:12:36,287
to reload data.                 
Why do we need to reload data?  

253
00:12:36,356 --> 00:12:38,656
Cuz we just added               
emoji to our model and          

254
00:12:38,725 --> 00:12:42,393
anytime you change the model    
you need to update your table.  

255
00:12:42,461 --> 00:12:44,228
So I'm gonna reload and         
cause it to go back,            

256
00:12:44,297 --> 00:12:47,031
look at my new model,           
call all those functions,       

257
00:12:47,099 --> 00:12:50,468
all these functions right       
here, reload everything.        

258
00:12:50,537 --> 00:12:52,837
It's also gonna nicely          
reload section zero and         

259
00:12:52,905 --> 00:12:56,774
put the button back because     
I set this back to false. So    

260
00:12:56,843 --> 00:12:58,409
let's see all of                
this in action.                 

261
00:13:06,385 --> 00:13:09,053
Here we go. So,                 
we've got this, we can still    

262
00:13:09,121 --> 00:13:12,556
scroll around, normally. We     
can reposition these things.    

263
00:13:12,625 --> 00:13:14,625
It won't let us put             
it in section 0,                

264
00:13:14,694 --> 00:13:18,062
that's good. We hit plus It     
brings up the text field.       

265
00:13:18,131 --> 00:13:19,363
It reloaded that section and    

266
00:13:19,432 --> 00:13:22,467
put the text field because we   
are adding a module right now.  

267
00:13:22,535 --> 00:13:26,804
Can bring up my keyboard        
down here, let's put some       

268
00:13:26,872 --> 00:13:29,373
sea creatures in here.          
I'm just gonna do that. Now,    

269
00:13:29,442 --> 00:13:32,677
I'm gonna hit return which      
gonna dismiss my keyboard       

270
00:13:32,745 --> 00:13:35,013
because of that resign first    
responder that put in there.    

271
00:13:35,081 --> 00:13:36,480
And since that's                
gonna end editing,              

272
00:13:36,549 --> 00:13:41,485
it's gonna add this emoji to    
our list. See that? Their       

273
00:13:41,554 --> 00:13:44,822
they are at the beginning. And  
we can do the same thing here.  

274
00:13:44,891 --> 00:13:46,757
Maybe I will add,               
I don't know,                   

275
00:13:46,826 --> 00:13:49,626
some farm animals here.         
And this time I'm not           

276
00:13:49,695 --> 00:13:52,229
gonna return, I'm actually      
going to dismiss my keyboard    

277
00:13:52,298 --> 00:13:54,431
by pressing the thing in        
the lower right corner.         

278
00:13:54,500 --> 00:13:56,734
You see that thing, that says   
keyboard go away. Ready,        

279
00:13:56,803 --> 00:14:01,972
boom and now it added those.    
So that' it,                    

280
00:14:02,041 --> 00:14:05,542
that's text field. Sorry we     
had to rush, kinda rush that,   

281
00:14:05,611 --> 00:14:08,379
but we, again, we got a lot of  
other stuff to cover. And I'll  

282
00:14:08,447 --> 00:14:10,815
be posting this code, so you    
can look at it in detail and    

283
00:14:10,884 --> 00:14:12,549
see. I showed you all           
the changes we made,            

284
00:14:12,618 --> 00:14:14,351
I just didn't                   
type them all in,               

285
00:14:14,420 --> 00:14:20,491
as we went along. All right,    
back to the slides right here.  

286
00:14:20,559 --> 00:14:23,160
Let's get to our main topic     
today, which is persistence.    

287
00:14:23,229 --> 00:14:26,764
By persistence, I mean making   
things stick around, right?     

288
00:14:26,833 --> 00:14:29,333
The user inputs some stuff,     
they create an emoji art        

289
00:14:29,402 --> 00:14:31,836
document or something like      
that. And you, of course,       

290
00:14:31,904 --> 00:14:33,771
want those things to stay       
around you don't want them to   

291
00:14:33,840 --> 00:14:36,040
disappear every time you run    
the app. Which is the case in   

292
00:14:36,108 --> 00:14:38,042
your homework and the case      
of emoji art right now,         

293
00:14:38,111 --> 00:14:40,545
which is kinda useless.         
So there's a lot of ways to     

294
00:14:40,614 --> 00:14:42,313
make things persistent          
as you can see so               

295
00:14:42,382 --> 00:14:44,982
let's dive right in and         
talk about all of them.         

296
00:14:45,051 --> 00:14:47,885
Now,some of them I'm only       
gonna cover a little bit and    

297
00:14:47,953 --> 00:14:50,888
some of them I'm gonna cover    
in depth. The first one here    

298
00:14:50,956 --> 00:14:54,525
is UserDefault, now this        
one is super duper simple,      

299
00:14:54,594 --> 00:14:58,329
it's kind like the dictionary   
that persists, right?           

300
00:14:58,398 --> 00:15:00,698
You put things in this          
dictionary with keys and        

301
00:15:00,767 --> 00:15:03,200
values and when you run         
your app the next time,         

302
00:15:03,269 --> 00:15:07,671
they're still there. The only   
restriction on that though,     

303
00:15:07,740 --> 00:15:10,207
is that the only things you     
can put in this dictionary      

304
00:15:10,276 --> 00:15:12,910
thing is property lists.        

305
00:15:12,979 --> 00:15:14,912
Okay now a property             
list is not a type, or          

306
00:15:14,981 --> 00:15:17,582
anything like that,             
it's just a concept.            

307
00:15:17,650 --> 00:15:19,817
A property list is              
any combination,                

308
00:15:19,886 --> 00:15:23,520
any data structure, that is     
any combination of only array,  

309
00:15:23,589 --> 00:15:27,158
dictionary, string, date,       
data or a number like bloat,    

310
00:15:27,227 --> 00:15:30,361
hint or double. Okay that's     
what we call a property list.   

311
00:15:30,430 --> 00:15:33,030
And that's the only thing       
you can put in this little      

312
00:15:33,099 --> 00:15:36,067
lightweight database called     
UserDefaults, all right?        

313
00:15:36,135 --> 00:15:39,037
So what does the API look       
like, to put things in there?   

314
00:15:39,105 --> 00:15:42,639
Very simple, it's got two       
main methods here, set,         

315
00:15:42,708 --> 00:15:46,244
with a property list as         
the argument for a key.         

316
00:15:46,312 --> 00:15:50,648
And then object for a key       
that returns a property list.   

317
00:15:50,717 --> 00:15:52,649
The reason that's an NE right   
there is that there's really    

318
00:15:52,718 --> 00:15:55,453
no other type that would        
represent a Property List, and  

319
00:15:55,522 --> 00:15:57,121
this is an Objective-C API.     

320
00:15:57,190 --> 00:16:01,826
But that NE has to be a thing   
that is a Property List. So     

321
00:16:01,895 --> 00:16:04,362
it could be an int. It could    
be an array of strings.         

322
00:16:04,430 --> 00:16:06,531
It could be a dictionary        
whose keys are strings and      

323
00:16:06,599 --> 00:16:08,733
whose values                    
are arrays of doubles.          

324
00:16:08,801 --> 00:16:11,502
Those would all be considered   
property lists. But             

325
00:16:11,571 --> 00:16:15,572
an array of CG float?           
Not a property list,            

326
00:16:15,641 --> 00:16:21,445
because a CG float is not       
a property list. All right,     

327
00:16:21,514 --> 00:16:23,213
so how do you read and          
write this stuff?               

328
00:16:23,282 --> 00:16:25,449
How do you access this? How do  
you call those methods? Well,   

329
00:16:25,517 --> 00:16:29,419
we don't actually create a      
different UserDefaults thing.   

330
00:16:29,488 --> 00:16:32,156
You can, but we don't usually   
do that. We instead used        

331
00:16:32,225 --> 00:16:34,925
a shared one we get by saying   
UserDefaults.standard.          

332
00:16:34,994 --> 00:16:39,063
Standard is a static bar in     
the user's evolved class, and   

333
00:16:39,131 --> 00:16:42,533
it returns to this shared       
UserDefaults thing. And         

334
00:16:42,601 --> 00:16:45,769
then we just set call set on    
it to set values, and we can    

335
00:16:45,838 --> 00:16:50,774
call object uptight or forKey   
rather, to get things back.     

336
00:16:50,843 --> 00:16:52,476
And so here's a bunch           
of examples of sets.            

337
00:16:52,545 --> 00:16:53,844
Notice I can just set a float,  

338
00:16:53,913 --> 00:16:54,745
because that's                  
a property list.                

339
00:16:54,814 --> 00:16:57,281
I can set an array of ints,     
that's a property list.         

340
00:16:57,350 --> 00:16:59,717
I can also set nil,             
because it's an Any?, and       

341
00:16:59,785 --> 00:17:02,787
that means clear                
out any value for               

342
00:17:02,855 --> 00:17:08,626
this key. And there's some      
convenience methods for         

343
00:17:08,694 --> 00:17:11,328
getting things out, right,      
cuz if you do object for        

344
00:17:11,397 --> 00:17:14,731
key, what type are you gonna    
get back? An any, which means   

345
00:17:14,800 --> 00:17:18,503
you're gonna have to use as to  
turn it into something. Well,   

346
00:17:18,571 --> 00:17:20,405
to save you that they           
have some methods and           

347
00:17:20,473 --> 00:17:23,207
they're like double forKey,     
array forKey and                

348
00:17:23,275 --> 00:17:26,944
those will return you that      
type. Now, for example,         

349
00:17:27,013 --> 00:17:30,248
double forKey, if the thing     
in there is not a double,       

350
00:17:30,316 --> 00:17:33,117
it's just gonna return 0.       
Cuz it's not a question mark,   

351
00:17:33,186 --> 00:17:36,254
unfortunately, it's             
just double. And                

352
00:17:36,322 --> 00:17:39,056
similarly, an array forKey,     
if the thing in there,          

353
00:17:39,124 --> 00:17:41,792
if that key is not an array,    
it's gonna return nil,          

354
00:17:41,861 --> 00:17:44,594
because that is an optional     
array. So these little things,  

355
00:17:44,663 --> 00:17:45,996
these conveniences              
try to help you but             

356
00:17:46,065 --> 00:17:47,832
they're only gonna help         
you as much as they can.        

357
00:17:47,901 --> 00:17:50,033
If you put the wrong types      
in there, obviously,            

358
00:17:50,102 --> 00:17:53,504
they can't do the right thing.  
When am I ever gonna use this   

359
00:17:53,573 --> 00:17:55,640
thing?                          
This thing is really only for   

360
00:17:55,708 --> 00:17:59,010
lightweight stuff like          
settings, preferences,          

361
00:17:59,078 --> 00:18:01,278
that kinda stuff. You           
wouldn't store documents or     

362
00:18:01,347 --> 00:18:05,082
any kind of serious user data   
in there with user defaults.    

363
00:18:05,151 --> 00:18:08,318
Now saving the database,        
the database is autosaved for   

364
00:18:08,387 --> 00:18:10,988
you. So you really don't have   
to save it. But sometimes you   

365
00:18:11,056 --> 00:18:13,524
want to, most notably when      
you're in debugging and         

366
00:18:13,593 --> 00:18:15,560
you're hitting stop in          
the debugger all the time.      

367
00:18:15,628 --> 00:18:18,528
Sometimes you'll stop it        
before it gets a chance to      

368
00:18:18,597 --> 00:18:20,431
save. So                        
if you wanna explicitly save,   

369
00:18:20,500 --> 00:18:23,133
you can use this method         
synchronize, which will save    

370
00:18:23,202 --> 00:18:25,303
it. It returns a bool whether   
it was successful, although I   

371
00:18:25,371 --> 00:18:27,204
don't know what you're gonna    
do if it wasn't successful.     

372
00:18:27,272 --> 00:18:28,772
I guess try again               
in a little bit.                

373
00:18:28,841 --> 00:18:32,242
But we usually don't look at    
the return value of this.       

374
00:18:32,311 --> 00:18:34,979
We just say synchronize. So     
a lot of times people will put  

375
00:18:35,047 --> 00:18:37,214
synchronize in there because    
they're doing the debugger,     

376
00:18:37,283 --> 00:18:38,882
and they're hitting             
stop all the time,              

377
00:18:38,951 --> 00:18:41,452
and it didn't save them, and    
then they run it again. So      

378
00:18:41,521 --> 00:18:42,787
you can feel free to            
do that if you want.            

379
00:18:42,855 --> 00:18:46,858
It's pretty lightweight to do   
synchronize. All right, so      

380
00:18:46,926 --> 00:18:49,927
that's the first one.           
The second way to make          

381
00:18:49,996 --> 00:18:53,564
things persistent is called     
archiving. So the problem with  

382
00:18:53,633 --> 00:18:56,099
user defaults, first of all,    
only small things.              

383
00:18:56,168 --> 00:18:59,236
Second of all, has to be        
property lists. What if I have  

384
00:18:59,304 --> 00:19:03,173
some data structure that I      
wanna store, that's big and or  

385
00:19:03,242 --> 00:19:06,943
has things other than property  
lists in it. And to do that     

386
00:19:07,012 --> 00:19:10,247
I'm gonna use archiving.        
Now there's two mechanisms for  

387
00:19:10,316 --> 00:19:14,451
archiving, an old way,          
and a new for iOS 11 way.       

388
00:19:14,520 --> 00:19:17,154
And of course, I'm gonna talk   
in detail about the new for     

389
00:19:17,223 --> 00:19:19,857
iOS 11 way, because the old     
way obviously wasn't good       

390
00:19:19,926 --> 00:19:22,593
enough. They came up            
with a new one in iOS 11.       

391
00:19:22,661 --> 00:19:24,461
But they're very,               
very similar in some ways.      

392
00:19:24,530 --> 00:19:26,831
It's just that the new way      
is a lot more automatic, and    

393
00:19:26,899 --> 00:19:29,933
a lot less code to write.       
So let's talk about these two   

394
00:19:30,002 --> 00:19:32,536
ways. The old way               
is called NS Coder.             

395
00:19:32,605 --> 00:19:35,639
So NS Coder is a protocol. And  

396
00:19:35,708 --> 00:19:39,677
essentially NS Coder boils      
down to having every single     

397
00:19:39,746 --> 00:19:43,947
object in the object graph      
that you want to save, or       

398
00:19:44,016 --> 00:19:47,717
whatever, make persistent,      
implement these two things.     

399
00:19:47,786 --> 00:19:49,987
A function called               
encode with a coder.            

400
00:19:50,056 --> 00:19:53,323
So that NS coder kind of        
like is a dictionary thing,     

401
00:19:53,392 --> 00:19:56,394
you can set values in there.    
And then init from coder.       

402
00:19:56,462 --> 00:19:58,729
It's gonna potentially give     
you that dictionary back and    

403
00:19:58,798 --> 00:20:02,199
you gotta initialize the        
object. So it's very simple.    

404
00:20:02,268 --> 00:20:05,102
You're just gonna have encode   
sent to every single object in  

405
00:20:05,170 --> 00:20:08,038
the object graph. And it's      
gonna put itself like in a big  

406
00:20:08,107 --> 00:20:10,374
dictionary. And then when you   
wanna bring it back to life,    

407
00:20:10,443 --> 00:20:13,110
you start telling init          
with the coder and              

408
00:20:13,179 --> 00:20:15,112
they all have to                
initialize themselves.          

409
00:20:15,181 --> 00:20:19,683
This is how storyboards         
are saved. So view Controller,  

410
00:20:19,752 --> 00:20:22,653
UI View, UI Label Button,       
all of them implement           

411
00:20:22,722 --> 00:20:26,089
both of these things in code    
and init from coder. And        

412
00:20:26,158 --> 00:20:28,759
somebody went to a painstaking  
amount of work to implement     

413
00:20:28,828 --> 00:20:31,028
that for every possible thing   
that can be in a storyboard.    

414
00:20:31,097 --> 00:20:34,465
It's amazing how much work      
that actually took. So          

415
00:20:34,533 --> 00:20:37,467
that's great, you have this     
encoding, encoding and          

416
00:20:37,536 --> 00:20:39,503
decoding ability.               
What do you do with it?         

417
00:20:39,571 --> 00:20:42,172
Well, what you almost always    
do with it is you turn this     

418
00:20:42,241 --> 00:20:46,476
thing into a data. Remember     
our friend data, bag of bits,   

419
00:20:46,545 --> 00:20:49,146
that little struct? You turn    
into a data, and then you       

420
00:20:49,214 --> 00:20:50,680
can store a data                
in a file system.               

421
00:20:50,749 --> 00:20:51,882
Cuz as you're gonna learn,      

422
00:20:51,951 --> 00:20:54,552
that's how we interact with     
the file system. We store and   

423
00:20:54,620 --> 00:20:58,923
read datas. So how do you take  
a big object graph, where       

424
00:20:58,991 --> 00:21:01,191
every single object in there    
implements these two things,    

425
00:21:01,260 --> 00:21:04,395
and turn it into a data? You    
do it with the class NS keyed   

426
00:21:04,463 --> 00:21:08,131
archiver. So NS keyed archiver  
just takes an object that       

427
00:21:08,200 --> 00:21:10,934
it and everything it points to  
implements these two things,    

428
00:21:11,003 --> 00:21:14,338
and it gives you back a data    
that has taken the whole        

429
00:21:14,407 --> 00:21:17,074
object graph, and               
collected it up into a data.    

430
00:21:17,143 --> 00:21:20,143
And similarly, if you give      
it back a data like that,       

431
00:21:20,212 --> 00:21:21,612
to NS keyed unarchiver,         

432
00:21:21,681 --> 00:21:25,182
the unarchiver then it will     
turn it back into the objects   

433
00:21:25,250 --> 00:21:27,751
by calling that init.           
Is everyone cool with how we    

434
00:21:27,820 --> 00:21:30,654
do that? This is a lot of work  
to make this mechanism work     

435
00:21:30,722 --> 00:21:32,522
because you've gotta implement  
those two things for            

436
00:21:32,591 --> 00:21:34,624
every single object in there.   
So                              

437
00:21:34,693 --> 00:21:36,660
let's talk about the new way,   
which is quite similar.         

438
00:21:36,729 --> 00:21:39,730
It's called Codable.            
And Codable is a protocol,      

439
00:21:39,798 --> 00:21:43,366
it's actually two protocols,    
D-Codable and N-Codable. And    

440
00:21:43,435 --> 00:21:46,937
it works the same kind of way.  
You still have init and         

441
00:21:47,006 --> 00:21:48,339
you still have                  
an encode thing.                

442
00:21:48,407 --> 00:21:51,275
The difference is Swift and     
the runtime, and, and           

443
00:21:51,343 --> 00:21:54,445
the foundation will implement   
those two methods for you,      

444
00:21:54,513 --> 00:21:57,547
almost all the time. It just    
kind of implements them for     

445
00:21:57,616 --> 00:21:59,283
free, so                        
you don't have to do anything.  

446
00:21:59,352 --> 00:22:02,920
So as long as you are using     
kind of basic types in Swift,   

447
00:22:02,989 --> 00:22:05,222
including all the things        
that you see on this slide,     

448
00:22:05,291 --> 00:22:07,891
it just all magically works.    
So                              

449
00:22:07,960 --> 00:22:11,562
I'm gonna show you both how we  
then take an object graph and   

450
00:22:11,631 --> 00:22:13,264
turn it into a data             
with this mechanism,            

451
00:22:13,332 --> 00:22:15,732
which is slightly different     
than the key archiver thing.    

452
00:22:15,801 --> 00:22:17,701
And I'm also gonna show you     
what it looks like to make      

453
00:22:17,770 --> 00:22:21,004
something Codable, cuz to make  
it to do this, it has to be     

454
00:22:21,073 --> 00:22:23,139
Codable. It has to implement    
Codable. So let's look at       

455
00:22:23,208 --> 00:22:26,210
those. First let's look at how  
we turn it into a data. Here,   

456
00:22:26,278 --> 00:22:29,346
instead of turning it into      
just an arbitrary blob of data  

457
00:22:29,415 --> 00:22:32,449
that we don't know what it is,  
we actually encode it to        

458
00:22:32,518 --> 00:22:36,019
a known format like JSON.       
Everyone know what JSON is?     

459
00:22:36,088 --> 00:22:38,221
It's essentially just           
like this text format for       

460
00:22:38,290 --> 00:22:40,925
describing things on the        
Internet, passing data around.  

461
00:22:40,993 --> 00:22:44,561
And so JSON is a well-known     
format, and we can turn that    

462
00:22:44,630 --> 00:22:47,365
big object graph into           
a description of it,            

463
00:22:47,433 --> 00:22:50,667
that is JSON, amazingly.        
And there's another             

464
00:22:50,736 --> 00:22:53,770
encoder that can do this,       
that does property list, so.    

465
00:22:53,839 --> 00:22:56,073
This whole thing I was telling  
you about UserDefaults,         

466
00:22:56,142 --> 00:22:58,575
where everything's an array of  
strings or dates or numbers,    

467
00:22:58,644 --> 00:23:00,711
you can also turn it            
into something like that.       

468
00:23:00,779 --> 00:23:03,713
Those are the two encoders      
that come with iOS. And         

469
00:23:03,782 --> 00:23:04,848
how do you do this? Well,       

470
00:23:04,917 --> 00:23:08,151
you just have your              
object that's of mytype,        

471
00:23:08,220 --> 00:23:11,922
some type that you define.      
That type has to be Codable.    

472
00:23:11,990 --> 00:23:14,591
And as long as it's Codable     
and everything that it wants    

473
00:23:14,660 --> 00:23:18,061
to be archived inside of it is  
Codable, then you can say JSON  

474
00:23:18,130 --> 00:23:22,899
data equals try to JSON         
encode that object. And it's    

475
00:23:22,968 --> 00:23:25,468
gonna give you back a data      
blob, and in that data blob     

476
00:23:25,537 --> 00:23:29,206
is a JSON representation of     
your entire object graph,       

477
00:23:29,274 --> 00:23:33,143
which is pretty incredible.     
Now notice this does throw,     

478
00:23:33,212 --> 00:23:36,146
it's unlikely to throw when     
you're encoding, but it could   

479
00:23:36,215 --> 00:23:39,383
possibly have something where   
first, I don't know why, but    

480
00:23:39,452 --> 00:23:43,153
it couldn't encode it,          
it's possible it could throw.   

481
00:23:43,222 --> 00:23:45,956
By the way, if you have         
a data Blob that's JSON,        

482
00:23:46,025 --> 00:23:49,292
you might wanna look at it      
as a string. With JSON it's     

483
00:23:49,361 --> 00:23:52,929
always encoded as utf8. That's  
the string encoding it uses.    

484
00:23:52,998 --> 00:23:55,666
So you can always just take     
a data Blob like jsonData and   

485
00:23:55,735 --> 00:23:58,669
from that previous line there   
and create a string with it.    

486
00:23:58,737 --> 00:24:00,938
And all that string needs to    
know is what's the encoding?    

487
00:24:01,007 --> 00:24:06,677
You say it's .utf8. Which       
is Unicode 8bit encoding.       

488
00:24:06,746 --> 00:24:09,546
All right, now, what if you     
have a JSON representation of   

489
00:24:09,615 --> 00:24:10,881
your whole object graph and     

490
00:24:10,950 --> 00:24:13,116
you wanna create your           
object graph out of it?         

491
00:24:13,185 --> 00:24:16,520
Well you just use a JSON        
decoder and say decode.         

492
00:24:16,588 --> 00:24:20,024
Well then all you have to do    
here is specify The class or    

493
00:24:20,092 --> 00:24:22,625
struct of the top level         
thing in that JSON,             

494
00:24:22,694 --> 00:24:26,396
represented by that JSON. And   
give it the JSON data blob and  

495
00:24:26,465 --> 00:24:28,865
it will decode it.              
Now this also throws and        

496
00:24:28,934 --> 00:24:31,769
this is more likely to throw.   
Maybe your JSON data is         

497
00:24:31,837 --> 00:24:35,639
corrupted or malformed or       
something like that. And        

498
00:24:35,708 --> 00:24:38,175
it quite possible to make       
this all work, where you're     

499
00:24:38,243 --> 00:24:41,144
using some standard JSON from   
some website out there and      

500
00:24:41,213 --> 00:24:43,780
you're converting it to         
objects in your code.           

501
00:24:43,849 --> 00:24:45,582
Where you make it do            
a one to one mapping.           

502
00:24:45,651 --> 00:24:48,686
And so maybe the website you    
went to had an error and        

503
00:24:48,754 --> 00:24:52,856
they generated bad JSON or      
something, so this could throw  

504
00:24:52,924 --> 00:24:55,626
here. And let's talk, we'll     
talk a little about that in     

505
00:24:55,694 --> 00:24:58,862
a second and what to do         
with that thing throwing.       

506
00:24:58,931 --> 00:25:03,133
Notice that JSON is the         
opposite of "strongly typed".   

507
00:25:03,202 --> 00:25:07,237
Like a date in JSON is just a   
string in some format, right?   

508
00:25:07,306 --> 00:25:11,041
There's no such concept as      
a date type in JSON. So this    

509
00:25:11,109 --> 00:25:14,444
decoder is quite configurable,  
so you can specify things       

510
00:25:14,513 --> 00:25:18,615
like, what is the strategy to   
decode what should be a date?   

511
00:25:18,683 --> 00:25:20,166
what format are dates stored    
in in this JSON file? So you    

512
00:25:20,167 --> 00:25:21,650
In other words,                 

513
00:25:21,720 --> 00:25:25,055
can specify those kinda things  
to configure the decoder to be  

514
00:25:25,124 --> 00:25:29,325
able to figure out this JSON    
representation. All right,      

515
00:25:29,394 --> 00:25:32,429
now I talked about throwing     
errors. Here, for example,      

516
00:25:32,498 --> 00:25:36,232
I'm catching a error that       
was thrown by this decoder.     

517
00:25:36,301 --> 00:25:38,101
And the reason I'm showing      
this actually is not because    

518
00:25:38,170 --> 00:25:40,404
you're going to do this.        
You're unlikely to actually     

519
00:25:40,472 --> 00:25:43,173
catch these decoding errors     
and do anything about them.     

520
00:25:43,242 --> 00:25:45,409
Unless maybe you're debugging   
your own JSON format,           

521
00:25:45,478 --> 00:25:47,744
you wanna see where you made    
a mistake or something.         

522
00:25:47,813 --> 00:25:50,147
But I wanted to show you here   
what it looks like to catch     

523
00:25:50,215 --> 00:25:54,951
an error that is thrown that's  
an enum. Cuz remember that      

524
00:25:55,020 --> 00:25:58,154
anything can be thrown. You     
can throw any kind of thing as  

525
00:25:58,223 --> 00:26:00,557
an error. All it has to do is   
implement the protocol error,   

526
00:26:00,625 --> 00:26:03,493
which is really nothing,        
so you can throw anything.      

527
00:26:03,562 --> 00:26:06,529
So a lot of times things will   
throw an enum. And when they    

528
00:26:06,598 --> 00:26:09,366
throw the enum, you can do the  
same thing we do with switch,   

529
00:26:09,435 --> 00:26:11,468
which is to grab                
the associated values out.      

530
00:26:11,536 --> 00:26:15,739
So you see how that really      
works great for errors, right?  

531
00:26:15,808 --> 00:26:18,007
So you're catching the key      
not found error and             

532
00:26:18,076 --> 00:26:19,376
you're grabbing                 
the associated value,           

533
00:26:19,444 --> 00:26:23,279
which is, one of which is       
the key that was not found. So  

534
00:26:23,348 --> 00:26:25,816
this is a common thing to do,   
is to throw an enum and         

535
00:26:25,885 --> 00:26:28,084
then in your catch you          
just catch the cases and        

536
00:26:28,153 --> 00:26:31,956
you're allowed to do this same  
kind of grab the associated     

537
00:26:32,024 --> 00:26:37,194
value as you can do             
with switch. All right,         

538
00:26:37,263 --> 00:26:39,896
so let's look at an example of  
making something be codable.    

539
00:26:39,965 --> 00:26:42,399
So I've got my struct           
MyType here. And                

540
00:26:42,468 --> 00:26:44,367
it's got a date in it,          
a string, and                   

541
00:26:44,436 --> 00:26:46,837
then it's got some other bar    
which is some other type        

542
00:26:46,906 --> 00:26:49,372
not shown here.                 
And to make it codable,         

543
00:26:49,441 --> 00:26:53,743
all I have to do is say colon   
codable. If I say that it's     

544
00:26:53,812 --> 00:26:58,215
codable, then it is codable.    
Unless it or something inside   

545
00:26:58,284 --> 00:27:01,484
of it can't be coded            
automatically by swift. So      

546
00:27:01,553 --> 00:27:03,921
it's not one of those things    
that I showed you on the first  

547
00:27:03,989 --> 00:27:07,157
slide there. So here,           
date is definitely codable,     

548
00:27:07,225 --> 00:27:08,892
string is codable,              
and presumably,                 

549
00:27:08,961 --> 00:27:12,462
some other type has made        
itself codable as well. And     

550
00:27:12,531 --> 00:27:15,666
so, this thing is now codable,  
and that's all I have to do.    

551
00:27:15,734 --> 00:27:18,301
A lot easier that implementing  
init and encode for             

552
00:27:18,370 --> 00:27:21,438
every single object in there.   
We just say it's codable, and   

553
00:27:21,507 --> 00:27:24,274
it is. And the JSON that would  
be generated from using that    

554
00:27:24,343 --> 00:27:26,710
JSON encoder would look         
something like this, right?     

555
00:27:26,778 --> 00:27:29,846
someDate, which is the same     
name as the var, colon, and     

556
00:27:29,915 --> 00:27:32,949
then the date in some encoding  
strategy that we decide.        

557
00:27:33,018 --> 00:27:36,486
And then "someString" :         
"Hello", and then "other" :     

558
00:27:36,555 --> 00:27:40,156
<whatever SomeOtherType looks   
like in JSON> looks like would  

559
00:27:40,225 --> 00:27:44,194
be embedded in there, you see?  
And so it can be recursively    

560
00:27:44,263 --> 00:27:48,965
going down.                     
Now we might not want the JSON  

561
00:27:49,034 --> 00:27:52,702
to look exactly like this, so   
can we tune this? Yeah we can,  

562
00:27:52,771 --> 00:27:57,007
look at this. In JSON, for      
example, the keys usually       

563
00:27:57,075 --> 00:28:00,443
don't have camel case, you      
know like some capital D data   

564
00:28:00,512 --> 00:28:03,513
like we do for our variables.   
Usually the keys are,           

565
00:28:03,582 --> 00:28:07,183
the words are separate with     
underbar like "som_date". So    

566
00:28:07,252 --> 00:28:10,787
we can easily change the keys   
that are generated when we use  

567
00:28:10,856 --> 00:28:15,158
that JSON coder by adding a     
private enum called CodingKeys  

568
00:28:15,227 --> 00:28:17,327
which is a string-type enum.    
And                             

569
00:28:17,396 --> 00:28:19,830
it has to implement             
a protocol coding key. And      

570
00:28:19,899 --> 00:28:22,799
all it does is has a case,      
it's an enum, right?            

571
00:28:22,868 --> 00:28:25,168
Has a case for every var        
that we want encoded.           

572
00:28:25,237 --> 00:28:26,870
So if we have a var we          
don't want encoded,             

573
00:28:26,939 --> 00:28:28,672
just don't put that             
case there. And                 

574
00:28:28,741 --> 00:28:30,340
if you have a var that          
you do want encoded, but        

575
00:28:30,409 --> 00:28:33,510
you want it to change the key,  
just say equals the key you     

576
00:28:33,578 --> 00:28:36,946
want. So here I've said case    
someDate = "som_date", so       

577
00:28:37,015 --> 00:28:40,550
now in the JSON it's gonna say  
som_date equals, instead of     

578
00:28:40,619 --> 00:28:43,687
someDate. And notice I didn't   
put someString case in there    

579
00:28:43,756 --> 00:28:46,490
at all, so someString is not    
even gonna be put in the JSON.  

580
00:28:48,427 --> 00:28:50,894
So this is a really cool,       
simple way to                   

581
00:28:50,963 --> 00:28:55,065
customize the JSON that you     
generate from your type. Now,   

582
00:28:55,134 --> 00:28:57,400
I'm not even gonna really       
talk about this, but            

583
00:28:57,469 --> 00:29:01,537
you can implement init from     
decoder. The thing that         

584
00:29:01,606 --> 00:29:05,641
actually pulls the thing out    
of the jJSON. If you want       

585
00:29:05,710 --> 00:29:08,411
to do some validation or some   
kind of complicated thing, or   

586
00:29:08,480 --> 00:29:12,282
if for example you have a type  
that swift can't encode.        

587
00:29:12,351 --> 00:29:15,418
Some new type that you          
invented that's not made up of  

588
00:29:15,487 --> 00:29:18,188
other types that swift can      
encode and you wanna do it,     

589
00:29:18,257 --> 00:29:20,490
you can do it. I just put       
this here as kind of,           

590
00:29:20,558 --> 00:29:23,426
so you can look at it later     
to see how you do it.           

591
00:29:23,495 --> 00:29:25,561
There's a container in          
the decoder and you get it and  

592
00:29:25,630 --> 00:29:28,431
it's got keys and values that   
looks like a dictionary. It's   

593
00:29:28,500 --> 00:29:32,402
not that hard. One thing is     
when you're decoding a class,   

594
00:29:32,471 --> 00:29:34,838
you have to be here for         
the call supe_init, right?      

595
00:29:34,907 --> 00:29:37,073
Cuz you're decoding,            
you have to implement init.     

596
00:29:37,142 --> 00:29:39,575
So you gotta call supe_init.    
But don't call supe_init        

597
00:29:39,644 --> 00:29:42,546
with the same decoder that was  
sent to you. Decoder was sent   

598
00:29:42,614 --> 00:29:46,283
to you is for decoding your     
vars. You want to send this     

599
00:29:46,351 --> 00:29:49,153
thing from the container        
called superDecoder.            

600
00:29:49,221 --> 00:29:52,889
As the decoder of your          
superclasses bars. And          

601
00:29:52,958 --> 00:29:56,860
then of course, you could also  
implement encoding to encode    

602
00:29:56,929 --> 00:29:59,496
random types that aren't        
part of the swifting.           

603
00:29:59,564 --> 00:30:00,864
Again, I'm not                  
gonna go over this.             

604
00:30:00,933 --> 00:30:01,832
You won't have to               
do any of this for              

605
00:30:01,900 --> 00:30:04,734
your homework of course.        
But for your final project      

606
00:30:04,803 --> 00:30:07,571
at least you know this can be   
done, is to implement encode    

607
00:30:07,639 --> 00:30:11,040
and init for yourself.          
All right, so that's it for     

608
00:30:11,109 --> 00:30:14,177
archiving. Archiving, the       
whole point is we take some     

609
00:30:14,246 --> 00:30:17,413
object graphed of swift stuff   
and we turn it into a data.     

610
00:30:17,482 --> 00:30:18,915
And the data is either          
gonna be JSON or                

611
00:30:18,984 --> 00:30:21,217
property list format.           
So we have a data,              

612
00:30:21,286 --> 00:30:24,487
now we wanna store that         
data in the file system.        

613
00:30:24,556 --> 00:30:25,588
We're gonna put it in a file.   

614
00:30:25,657 --> 00:30:29,426
It's just a normal file.        
Remember that iOS is Unix. And  

615
00:30:29,495 --> 00:30:32,929
so we have a unix filesystem    
underneath of course and        

616
00:30:32,998 --> 00:30:36,500
starts at slash any other       
of the unix file system and     

617
00:30:36,568 --> 00:30:39,502
all we need to do to store our  
data blog is just write it      

618
00:30:39,571 --> 00:30:43,740
to a file. So how do we access  
this unix file system in iOS?   

619
00:30:43,809 --> 00:30:45,909
Well, the most                  
important thing to              

620
00:30:45,977 --> 00:30:48,712
understand is that the only     
part of Unix file system you    

621
00:30:48,780 --> 00:30:53,116
can access is your sand box.    
Your sandbox is this little     

622
00:30:53,184 --> 00:30:55,418
enclosed space. It's the only   
place you can write.            

623
00:30:55,487 --> 00:30:57,887
You can't write into any        
system files anywhere.          

624
00:30:57,956 --> 00:30:59,889
You can't write into any        
other app's information.        

625
00:30:59,958 --> 00:31:02,692
You can only write in your      
sandbox. Why does iOS           

626
00:31:02,761 --> 00:31:07,731
restrict you to a sandbox.      
Well, three main reasons.       

627
00:31:07,799 --> 00:31:12,636
One, Security. Because we want  
to make sure that no other      

628
00:31:12,704 --> 00:31:16,473
app can come along and break    
your app somehow, make it so    

629
00:31:16,542 --> 00:31:19,810
that your app doesn't work.     
Privacy,                        

630
00:31:19,878 --> 00:31:21,845
you're collecting user          
information, whatever,          

631
00:31:21,914 --> 00:31:24,080
you don't want other malicious  
apps to be looking in there     

632
00:31:24,149 --> 00:31:26,983
and getting that information.   
And an underrated one is        

633
00:31:27,052 --> 00:31:30,954
cleanup. You wanna be able to   
clean up when the user says,    

634
00:31:31,022 --> 00:31:34,090
I don't want this app anymore.  
If you have everything in       

635
00:31:34,159 --> 00:31:36,426
a sandbox, you can delete that  
sandbox, and now everything     

636
00:31:36,494 --> 00:31:39,595
that app has ever done is       
gone. So, there's the clean-up  

637
00:31:39,664 --> 00:31:43,666
part of it. So, Access in the   
Unix file system is all about   

638
00:31:43,735 --> 00:31:47,103
finding a starting point in     
this sandbox. And there's       

639
00:31:47,172 --> 00:31:49,939
a few starting points that      
you can find. For example,      

640
00:31:50,008 --> 00:31:52,675
there is your application       
directory in the sandbox.       

641
00:31:52,744 --> 00:31:56,179
This has your executable, all   
your storyboards, JPEG files,   

642
00:31:56,248 --> 00:31:58,148
your image assets,              
all those things.               

643
00:31:58,216 --> 00:32:02,486
This part of your sandbox,      
you can get a Unix path to it.  

644
00:32:02,554 --> 00:32:04,654
But it's completely             
not writeable.                  

645
00:32:04,723 --> 00:32:07,323
You cannot write to any of      
this. You can only read it.     

646
00:32:07,392 --> 00:32:09,125
If there was something you      
needed to write in there,       

647
00:32:09,194 --> 00:32:12,229
like let's say you pass some    
initial database or something,  

648
00:32:12,297 --> 00:32:13,463
you would have to               
copy it out into                

649
00:32:13,531 --> 00:32:15,866
one of the other places         
in your sandbox, and            

650
00:32:15,934 --> 00:32:19,069
edit it from there.             
Another place in your sandbox,  

651
00:32:19,138 --> 00:32:21,771
really important,               
is the Documents directory.     

652
00:32:21,840 --> 00:32:25,041
This is where you store stuff   
that the user perceives         

653
00:32:25,110 --> 00:32:27,177
as their data in                
document form.                  

654
00:32:27,245 --> 00:32:30,146
And the reason it's important   
that it be user-perceived       

655
00:32:30,215 --> 00:32:33,083
as a document is because this   
directory, what's in there,     

656
00:32:33,152 --> 00:32:36,253
is gonna be visible in          
the files app in iOS 11.        

657
00:32:36,321 --> 00:32:39,756
I don't know if you all have    
seen iOS 11, played with it     

658
00:32:39,825 --> 00:32:42,559
much. There's a new app in      
there, Files, and it shows      

659
00:32:42,627 --> 00:32:45,362
you all the files in all the    
Document directories of all     

660
00:32:45,430 --> 00:32:48,598
the apps. So don't put things   
in the Documents directory      

661
00:32:48,666 --> 00:32:52,502
unless they're perceived        
as documents by the user.       

662
00:32:52,570 --> 00:32:54,704
There's also applications       
support. That's where you can   

663
00:32:54,773 --> 00:32:58,174
put the stuff that the user     
creates that's not a document,  

664
00:32:58,243 --> 00:33:00,610
because that's not gonna        
show up in Files. And           

665
00:33:00,679 --> 00:33:01,911
then there's other              
directories,                    

666
00:33:01,980 --> 00:33:03,914
about a dozen other ones.       
One of them, for example,       

667
00:33:03,982 --> 00:33:06,183
is Caches directory. That's     
where you can put temporary     

668
00:33:06,251 --> 00:33:09,052
stuff that can be deleted at    
any other time, at any time,    

669
00:33:09,121 --> 00:33:12,022
and recreated. For example, in  
your homework for this week,    

670
00:33:12,090 --> 00:33:14,190
I'm gonna ask you to take       
your image galleries and        

671
00:33:14,259 --> 00:33:18,161
cache those images. So that     
when people drag stuff in and   

672
00:33:18,229 --> 00:33:19,262
then they start                 
scrolling around,               

673
00:33:19,331 --> 00:33:20,463
instead of constantly           
going back and                  

674
00:33:20,531 --> 00:33:21,798
fetching those                  
things all the time,            

675
00:33:21,867 --> 00:33:23,299
you cache them in               
the file system. Well,          

676
00:33:23,368 --> 00:33:26,035
you're gonna wanna put that in  
the Caches directory because    

677
00:33:26,104 --> 00:33:28,905
it won't count against your     
app in terms of disk space      

678
00:33:28,973 --> 00:33:31,541
usage, and you can always just  
re-fetch it again if you,       

679
00:33:31,610 --> 00:33:35,312
if the cache gets blown away.   

680
00:33:35,380 --> 00:33:37,313
All right, so, you need to get  
paths to all these things.      

681
00:33:37,382 --> 00:33:40,450
So how do you get a path to     
these special directories, and  

682
00:33:40,518 --> 00:33:44,220
then start building on it       
to build your own paths.        

683
00:33:44,289 --> 00:33:46,622
Well the first thing to         
understand is that all          

684
00:33:46,691 --> 00:33:48,591
the access to the file system   
is gonna happen through         

685
00:33:48,660 --> 00:33:51,695
two classes, or two, two        
objects. They're not classes,   

686
00:33:51,764 --> 00:33:54,230
they're struct.                 
But one is FileManager,         

687
00:33:54,299 --> 00:33:57,466
and the other one is URL. And   
you've already learned about    

688
00:33:57,535 --> 00:34:01,137
URL because we've used URLs     
to the network resources,       

689
00:34:01,205 --> 00:34:03,840
HTTP resources, and things      
like that. Well, you can also   

690
00:34:03,908 --> 00:34:06,742
have URLs to local resources,   
things on your disk.            

691
00:34:06,811 --> 00:34:09,078
And our URL is                  
essentially just a path,        

692
00:34:09,147 --> 00:34:13,216
a Unix path to the file.        
So the,                         

693
00:34:13,284 --> 00:34:16,552
what you're gonna do before     
you do anything is find one     

694
00:34:16,621 --> 00:34:19,556
of these sandbox directories,   
cuz you cannot only write and   

695
00:34:19,625 --> 00:34:21,524
read from those sandbox         
directories. So                 

696
00:34:21,593 --> 00:34:26,362
there's really two methods      
to get a sandbox URL, and       

697
00:34:26,431 --> 00:34:28,498
I'm going to show you one of    
them here, which is, I kind of  

698
00:34:28,567 --> 00:34:31,701
prefer. I'll actually show the  
other one maybe in the demo.    

699
00:34:31,769 --> 00:34:35,605
It's a FileManager method, and  
the FileManager is kind of      

700
00:34:35,674 --> 00:34:38,274
like user default in that       
we use a shared one called      

701
00:34:38,343 --> 00:34:40,977
default. Although sometimes     
we would actually wanna         

702
00:34:41,046 --> 00:34:43,713
create a different FileManager  
by saying FileManager           

703
00:34:43,782 --> 00:34:45,515
open parentheses closed         
parentheses, right? Just        

704
00:34:45,584 --> 00:34:47,583
calling its initializer, which  
takes no argument, and I'll     

705
00:34:47,652 --> 00:34:50,786
talk about when we'd wanna do   
that a little bit later here.   

706
00:34:50,855 --> 00:34:54,524
So this one is called URL for   
directory in DomainMask,        

707
00:34:54,592 --> 00:34:59,162
appropriate for create. So      
let's look at these arguments.  

708
00:34:59,231 --> 00:35:02,331
The for directory is the        
sandbox directory you want.     

709
00:35:02,400 --> 00:35:05,067
Like the documentDirectory,     
the cachesDirectory,            

710
00:35:05,136 --> 00:35:06,970
the                             
applicationSupportDirectory.    

711
00:35:07,038 --> 00:35:08,671
That's there and                

712
00:35:08,740 --> 00:35:12,242
it's specified via              
an enum here. And               

713
00:35:12,310 --> 00:35:14,110
I show you some examples of     
what they are at the bottom.    

714
00:35:14,179 --> 00:35:16,879
You can obviously go look       
it up in the documentation,     

715
00:35:16,948 --> 00:35:19,749
what's available there.         
In domainMask, is always        

716
00:35:19,818 --> 00:35:23,185
.userDomainMask on iOS because  
we have the sandbox, and        

717
00:35:23,254 --> 00:35:25,155
we can only look                
in the sandbox.                 

718
00:35:25,223 --> 00:35:28,992
On MacOS it could be            
a shared network domain.        

719
00:35:29,060 --> 00:35:31,327
It could be the systems         
shared domain center, but       

720
00:35:31,396 --> 00:35:34,263
on iOS it's always              
userDomainMask right there.     

721
00:35:34,332 --> 00:35:37,266
Appropriate for just, you're    
always gonna set that to nil.   

722
00:35:37,335 --> 00:35:39,502
That's basically if you're      
gonna replace a file,           

723
00:35:39,571 --> 00:35:41,905
you want to specify the URL of  
what you're gonna replace so    

724
00:35:41,973 --> 00:35:44,840
you can make sure it's on       
the same volume as the,         

725
00:35:44,909 --> 00:35:48,545
the URL you are getting.        
Again, kind of not meaningful   

726
00:35:48,613 --> 00:35:51,213
in iOS most of the time, so     
that's usually just nil. And    

727
00:35:51,282 --> 00:35:52,616
then create is                  
an important one.               

728
00:35:52,684 --> 00:35:55,251
That says whether you're        
gonna create that sandbox,      

729
00:35:55,320 --> 00:35:56,386
special sandbox directory,      

730
00:35:56,455 --> 00:35:59,055
cuz not all of them exist       
when your app is created.       

731
00:35:59,123 --> 00:36:01,424
Like applicationSupport does    
not exist, so you'll have to    

732
00:36:01,493 --> 00:36:03,459
make sure you say create:       
true, right there. Doesn't      

733
00:36:03,528 --> 00:36:05,428
hurt to say create: true,       
I think documentDirectory       

734
00:36:05,496 --> 00:36:08,397
actually is already created     
for you, but, can't hurt. So    

735
00:36:08,466 --> 00:36:12,068
this is how you get a URL, you  
see the return value is a URL,  

736
00:36:12,136 --> 00:36:14,738
into the sandbox. Now that you  
have a URL in the sandbox,      

737
00:36:14,806 --> 00:36:17,607
now you can start writing       
files. And the way you do that  

738
00:36:17,675 --> 00:36:21,478
is by using the URL method      
appendingPathComponent.         

739
00:36:21,547 --> 00:36:24,213
So adds a directory or          
the name of a file              

740
00:36:24,282 --> 00:36:27,217
onto the end of that URL, you   
can even add file extensions.   

741
00:36:27,285 --> 00:36:28,317
It's perfectly legal,           
by the way,                     

742
00:36:28,386 --> 00:36:32,689
to say appendingPathComponent   
food.jpg, you don't have to     

743
00:36:32,757 --> 00:36:34,357
do the extension with           
a separate call there.          

744
00:36:34,426 --> 00:36:37,460
But anyway, you're gonna use    
that to build a URL that        

745
00:36:37,529 --> 00:36:40,663
extends past the sandbox, and   
it can have directories and     

746
00:36:40,731 --> 00:36:43,833
stuff. You can,                 
once you have URL,              

747
00:36:43,901 --> 00:36:47,069
you can find out about things   
like, is it a FileURL, or       

748
00:36:47,138 --> 00:36:50,806
is it an HTTP URL? You can get  
things like the right date.     

749
00:36:50,875 --> 00:36:54,144
Is this a directory?            
How big is this file?           

750
00:36:54,213 --> 00:36:57,714
From this method,               
resourceValues in URL.          

751
00:36:57,782 --> 00:37:00,683
And resourceValues for keys     
takes a bunch of keys, like     

752
00:37:00,752 --> 00:37:03,385
file size and stuff like that,  
and goes and looks it up in     

753
00:37:03,454 --> 00:37:06,555
the file system and returns a   
dictionary with those keys and  

754
00:37:06,624 --> 00:37:09,391
the value it found. That's why  
the value is Any right there.   

755
00:37:09,460 --> 00:37:13,363
It could be a number, it could  
be a string, things like that.  

756
00:37:13,431 --> 00:37:15,799
So you can find out a lot       
about your files there.         

757
00:37:17,235 --> 00:37:18,835
How do you read and             
write files?                    

758
00:37:18,904 --> 00:37:21,738
We do that with data.           
And you've already seen this,   

759
00:37:21,806 --> 00:37:26,075
actually. We used data to       
read a file off the internet,   

760
00:37:26,144 --> 00:37:29,078
with an HTTP URL. Of course     
you can do that with a FileURL  

761
00:37:29,147 --> 00:37:32,582
as well. We did not use         
the options when we did it,     

762
00:37:32,651 --> 00:37:34,083
because we used                 
the default options,            

763
00:37:34,152 --> 00:37:36,753
which you mostly will. But      
there are some read options     

764
00:37:36,822 --> 00:37:38,921
you can go look at.             
And to write files,             

765
00:37:38,990 --> 00:37:41,724
you're going to send this       
to data, write(to url.          

766
00:37:41,792 --> 00:37:45,061
And it also has options you     
can look at as well. So that    

767
00:37:45,129 --> 00:37:48,197
is how we read and and write    
to the file system. We have     

768
00:37:48,266 --> 00:37:51,401
a data, probably one we got by  
archiving the thing to JSON or  

769
00:37:51,469 --> 00:37:54,137
whatever with their archiver,   
and we just read and            

770
00:37:54,206 --> 00:37:57,606
write with these two methods    
from the file system. So        

771
00:37:57,675 --> 00:37:59,909
you can see it's all about      
just getting the right URL,     

772
00:37:59,978 --> 00:38:00,877
and then it's easy to read and  

773
00:38:00,946 --> 00:38:04,213
write. I want to talk           
a little bit more about         

774
00:38:04,282 --> 00:38:07,484
FileManager. You can do a lot   
of other things besides just    

775
00:38:07,552 --> 00:38:09,385
give you a URL of               
something in the sandbox.       

776
00:38:09,454 --> 00:38:12,355
For example, it can tell you    
whether a file exists, on,      

777
00:38:12,423 --> 00:38:15,658
in the file system.             
It can move files, copy files,  

778
00:38:15,726 --> 00:38:19,028
create directories, enumerate   
directories, delete files,      

779
00:38:19,097 --> 00:38:20,897
all that stuff,                 
all in FileManager.             

780
00:38:20,966 --> 00:38:23,433
FileManager has probably        
a hundred methods in it for     

781
00:38:23,502 --> 00:38:26,936
doing all that. FileManager     
also has a delegate. And        

782
00:38:27,005 --> 00:38:30,206
that delegate, almost all of    
the methods are, should this.   

783
00:38:30,275 --> 00:38:33,142
Should I allow opening this     
file? Should I allow you        

784
00:38:33,211 --> 00:38:35,044
to move this file. They're      
kind of should things, so       

785
00:38:35,113 --> 00:38:37,546
a delegate can control whether  
the FileManager is allowed to   

786
00:38:37,615 --> 00:38:41,917
do things. That and the fact    
that FileManager is thread      

787
00:38:41,986 --> 00:38:45,254
safe, but only within one       
instance of the FileManager.    

788
00:38:45,323 --> 00:38:47,757
So if you have a FileManager    
on another thread besides       

789
00:38:47,826 --> 00:38:49,592
the main thread,                
it's thread safe but            

790
00:38:49,661 --> 00:38:52,862
only if that FileManager        
was created on that thread.     

791
00:38:52,931 --> 00:38:55,731
And the filemanager.default     
that I showed you before,       

792
00:38:55,800 --> 00:38:57,967
that's the main thread one.     
So you don't want to use        

793
00:38:58,036 --> 00:39:00,470
filemanager.default in any      
of the thread, but the main     

794
00:39:00,538 --> 00:39:04,006
thread. And of course, if       
you're gonna set a delegate on  

795
00:39:04,075 --> 00:39:06,175
the FileManager, you probably   
don't want to set the delegate  

796
00:39:06,244 --> 00:39:09,178
of filemanager.default. That's  
kind of a shared FileManager    

797
00:39:09,247 --> 00:39:11,948
everybody's using in            
the main thread. So             

798
00:39:12,016 --> 00:39:15,384
you probably want to create     
a FileManager in that case.     

799
00:39:15,453 --> 00:39:18,421
Multiple FileManagers know how  
to not step on each others'     

800
00:39:18,490 --> 00:39:22,758
toes. All right? So we've       
learned the simple little       

801
00:39:22,827 --> 00:39:25,929
database, which was             
the user default thing          

802
00:39:25,997 --> 00:39:28,197
where we could store property   
lists for, that's just for      

803
00:39:28,266 --> 00:39:31,767
settings and stuff like that.   
Then we learned about how to    

804
00:39:31,836 --> 00:39:34,570
do archiving, much more         
powerful. We can store other    

805
00:39:34,639 --> 00:39:37,006
things and Swift will mostly    
just do the code for us,        

806
00:39:37,075 --> 00:39:40,843
but sometimes we can get        
involved if we want. And        

807
00:39:40,912 --> 00:39:44,080
it generates datas, then we     
learn how to take those datas,  

808
00:39:44,148 --> 00:39:46,782
with JSON or whatever in them,  
and store them in the file      

809
00:39:46,851 --> 00:39:49,852
system, using FileManager and   
URL. Now I'm gonna talk about   

810
00:39:49,921 --> 00:39:53,022
the next persistence thing      
which is core data. So          

811
00:39:53,091 --> 00:39:54,290
core data is if you have        

812
00:39:54,359 --> 00:39:57,159
a large amount of data and      
you need to search over it.     

813
00:39:57,228 --> 00:39:59,228
In other words,                 
you need a database.            

814
00:39:59,297 --> 00:40:03,566
So core data is essentially a   
SQL database. With an objected  

815
00:40:03,635 --> 00:40:06,902
oriented API. So you            
interact with this database.    

816
00:40:06,971 --> 00:40:10,272
It looks like Swift objects,    
but behind the scene those      

817
00:40:10,341 --> 00:40:13,343
Swift objects are actually in   
a database, a SQL database.     

818
00:40:13,411 --> 00:40:14,811
Now Core Data is                
very powerful and               

819
00:40:14,879 --> 00:40:17,480
can actually have back ends     
that are different than SQL,    

820
00:40:17,549 --> 00:40:21,951
but for the most part we use    
SQL back end for Core Data. So  

821
00:40:22,020 --> 00:40:24,987
that's what Core Data is,       
it's very efficient,            

822
00:40:25,056 --> 00:40:27,189
beautifully object oriented.    

823
00:40:27,258 --> 00:40:28,358
Now, I cannot,                  

824
00:40:28,426 --> 00:40:30,593
I don't have time in this       
quarter to talk about it, but   

825
00:40:30,662 --> 00:40:33,796
luckily, I spent a whole        
week on it last quarter. So     

826
00:40:33,865 --> 00:40:37,032
you can go and look on iTunes   
U and see two lectures on it,   

827
00:40:37,101 --> 00:40:38,267
it hasn't really                
changed that much for           

828
00:40:38,336 --> 00:40:41,103
iOS 11, so it'll all be good.   
This is a great                 

829
00:40:41,172 --> 00:40:43,739
not covered in lecture feature  
for your final project,         

830
00:40:43,808 --> 00:40:46,042
because I'm not really gonna    
cover it in this lecture.       

831
00:40:46,111 --> 00:40:47,943
I'm gonna kinda give you        
an overview of it. But          

832
00:40:48,012 --> 00:40:48,944
you can easily go back and      

833
00:40:49,013 --> 00:40:50,446
watch my last lecture and,      
boom,                           

834
00:40:50,515 --> 00:40:52,548
learn all about it and          
be ready to go. So              

835
00:40:52,617 --> 00:40:55,251
all I'm gonna do here is        
a brief overview of it.         

836
00:40:55,320 --> 00:40:56,886
If you want a detailed          
of Core Data, and               

837
00:40:56,954 --> 00:40:59,522
it is a great feature to        
do for your final project,      

838
00:40:59,591 --> 00:41:03,493
believe me. Go check            
that iTunes U. All right,       

839
00:41:03,561 --> 00:41:07,263
so it's a way of having this    
object-oriented programming     

840
00:41:07,331 --> 00:41:11,266
layer with the back end SQL.    
How do we do that, how do we    

841
00:41:11,335 --> 00:41:14,770
match those two things up?      
Well we actually have a tool    

842
00:41:14,839 --> 00:41:18,207
in Xcode which is a visual      
mapper. You build all your      

843
00:41:18,276 --> 00:41:21,611
objects and all their vars      
essentially in this mapper.     

844
00:41:21,680 --> 00:41:23,946
And the mapper is used to       
figure out how to do that       

845
00:41:24,015 --> 00:41:27,783
mapping forward for you, and    
it just happens automatically.  

846
00:41:27,852 --> 00:41:30,252
So if any of you who know       
about databases, databases      

847
00:41:30,321 --> 00:41:33,890
have tables. They have rows in  
the tables that are records,    

848
00:41:33,959 --> 00:41:36,059
they have columns               
which are the fields.           

849
00:41:36,127 --> 00:41:38,061
That's still happening          
behind the scenes, but          

850
00:41:38,129 --> 00:41:40,263
you don't see any of that       
when you're programming,        

851
00:41:40,331 --> 00:41:42,331
because you're using            
an object-oriented API.         

852
00:41:42,400 --> 00:41:45,401
So this is what the Visual      
Mapper looks like, right,       

853
00:41:45,470 --> 00:41:48,738
it's in Xcode here. And here    
I have a couple objects here,   

854
00:41:48,807 --> 00:41:50,773
a tweet and a twitter user.     

855
00:41:50,842 --> 00:41:53,042
And those are going to map      
to objects in my code and       

856
00:41:53,111 --> 00:41:55,811
tables in the database. And     
then we've got the fields like  

857
00:41:55,880 --> 00:41:57,380
the tweet's got                 
a created date,                 

858
00:41:57,448 --> 00:42:01,017
a unique identifier of the      
tweet, the text of the tweet.   

859
00:42:01,085 --> 00:42:03,819
And its even got a var which    
is the tweeter which points     

860
00:42:03,888 --> 00:42:06,723
over to the twitter user and    
on the twitter user side,       

861
00:42:06,791 --> 00:42:10,059
it's got a var called tweets.   
Which is gonna point back,      

862
00:42:10,127 --> 00:42:14,229
which is actually a set         
of tweet objects. So            

863
00:42:14,298 --> 00:42:17,332
this mapping is being used      
by Core Data on both sides.     

864
00:42:17,401 --> 00:42:18,467
On the object side to make      

865
00:42:18,536 --> 00:42:20,002
all of these things             
look like objects, and          

866
00:42:20,071 --> 00:42:21,537
on the other side to            
build the tables and            

867
00:42:21,606 --> 00:42:25,775
rows in the database. So        
let's at how we, what it kind   

868
00:42:25,844 --> 00:42:27,943
of looks like to do this        
in code so you get an idea.     

869
00:42:28,012 --> 00:42:30,112
Again, I'm not trying to teach  
you how to do Core Data here.   

870
00:42:30,181 --> 00:42:32,581
This is to kind of give you     
an idea of what it looks like.  

871
00:42:32,650 --> 00:42:34,684
The most important thing about  
core data to understand,        

872
00:42:34,753 --> 00:42:37,219
is that we access all           
of it from a code using         

873
00:42:37,288 --> 00:42:41,190
an NSManagedObjectContext.      
So this context is key and      

874
00:42:41,259 --> 00:42:43,693
there's two ways to             
get this context. One,          

875
00:42:43,762 --> 00:42:45,261
you know how when we            
created our project?            

876
00:42:45,330 --> 00:42:46,662
There was that little           
switch there, that said,        

877
00:42:46,731 --> 00:42:49,899
use core data, you remember     
that? So you can flip that on   

878
00:42:49,968 --> 00:42:53,335
and then you'll get a method    
in your app delegate, which we  

879
00:42:53,404 --> 00:42:55,304
haven't talked about. We'll     
talk about that next week,      

880
00:42:55,373 --> 00:42:57,340
that is giving                  
you the context.                

881
00:42:57,409 --> 00:42:59,041
It's actually a var that        
gives you the context.          

882
00:42:59,110 --> 00:43:02,078
So that's one way, another      
way is to create a subclass,    

883
00:43:02,146 --> 00:43:04,947
it's use a subclass of          
UIDocument, which I'm gonna     

884
00:43:05,015 --> 00:43:09,385
talk about later today. Which   
will give you the context,      

885
00:43:09,453 --> 00:43:12,488
and UIDocument is a way of      
abstracting a document.         

886
00:43:12,556 --> 00:43:14,523
So that's a way of looking      
at your entire database,        

887
00:43:14,592 --> 00:43:18,527
as just like one big document.  
It could be a huge document     

888
00:43:18,596 --> 00:43:21,230
cuz those databases             
can be big. But                 

889
00:43:21,299 --> 00:43:23,099
those are the two ways          
to get a context.               

890
00:43:23,167 --> 00:43:25,768
Once you have a two,            
a context in your hand,         

891
00:43:25,836 --> 00:43:28,604
now you can start doing all     
this access in the database     

892
00:43:28,672 --> 00:43:30,940
looking like an object. And     
here's what this looks like.    

893
00:43:31,008 --> 00:43:35,344
So here, for example, I'm       
creating a tweet. And the only  

894
00:43:35,412 --> 00:43:38,314
argument to the initializer     
there is the context,           

895
00:43:38,382 --> 00:43:40,817
which tells, is basically       
the database to put it in. But  

896
00:43:40,885 --> 00:43:42,785
then if I want to set           
the text of the tweet,          

897
00:43:42,854 --> 00:43:45,221
I just say tweet.text,          
it looks just like Swift,       

898
00:43:45,289 --> 00:43:49,058
tweet.created equals a date.    
Yeah I can even create Joe,     

899
00:43:49,126 --> 00:43:51,927
a twitter user in the same      
context as the tweet and        

900
00:43:51,996 --> 00:43:56,899
say tweet.tweeter = Joe. I can  
even go tweet.tweeter.name =    

901
00:43:56,967 --> 00:44:00,702
"Joe Schmo" in other words      
use Swift notation to go        

902
00:44:00,771 --> 00:44:03,672
through objects that            
I'm linked to. So               

903
00:44:03,741 --> 00:44:08,377
it really looks just exactly    
like Swift. And I can also      

904
00:44:08,446 --> 00:44:12,181
delete objects by just asking   
the context to delete them.     

905
00:44:12,250 --> 00:44:15,050
Changes that I made             
are actually autosaved if       

906
00:44:15,119 --> 00:44:18,587
I use that UIDocument approach  
to getting the context.         

907
00:44:18,656 --> 00:44:21,357
But if I used the Use Core      
Data switch to do it,           

908
00:44:21,425 --> 00:44:24,360
then I have to save it. The     
only thing about the save is    

909
00:44:24,428 --> 00:44:25,994
it can throw.                   
As you can imagine,             

910
00:44:26,063 --> 00:44:28,364
if I'm saving this stuff        
out to the SQL database,        

911
00:44:28,433 --> 00:44:30,966
I could get SQL errors or some  
kind of file system full or     

912
00:44:31,035 --> 00:44:34,203
things like that. So I have to  
catch the errors, if I'm not    

913
00:44:34,271 --> 00:44:37,907
gonna do the UIDocument based   
auto-saving. Now how about      

914
00:44:37,976 --> 00:44:41,143
searching for objects, tweets   
and twitter users in there.     

915
00:44:41,212 --> 00:44:42,912
So here I'm gonna search for    

916
00:44:42,981 --> 00:44:47,050
some twitter users that have    
tweeted in the last 24 hours.   

917
00:44:47,118 --> 00:44:49,418
So first, I asked               
the TwitterUser class for       

918
00:44:49,487 --> 00:44:51,987
a fetch request. You see        
the first line there where I'm  

919
00:44:52,056 --> 00:44:54,089
saying                          
TwitterUser.fetchRequest?       

920
00:44:54,158 --> 00:44:57,093
Then this fetch request,        
I set a predicate on it, see,   

921
00:44:57,162 --> 00:44:59,962
NSPredicate format?             
And predicate is a way of       

922
00:45:00,031 --> 00:45:04,299
specifying the search you want  
in text. It's not quite like    

923
00:45:04,368 --> 00:45:08,971
SQL, but it's very English      
oriented. So here I want any    

924
00:45:09,040 --> 00:45:13,809
tweets that were created        
after 24 hours ago. Okay        

925
00:45:13,877 --> 00:45:16,478
cuz yesterday is a var I made   
on the previous line which      

926
00:45:16,547 --> 00:45:21,350
is timeIntervalSinceNow         
minus 24 hours. So              

927
00:45:21,418 --> 00:45:22,651
I've described my               
search that way.                

928
00:45:22,720 --> 00:45:26,755
I also can describe how I want  
the result sorted. Here I'm     

929
00:45:26,824 --> 00:45:30,225
gonna sort them by the name     
of the TwitterUser. And         

930
00:45:30,294 --> 00:45:33,796
then I just asked the context   
please go fetch those things    

931
00:45:33,864 --> 00:45:37,533
that match that. And it gives   
me back an array of those       

932
00:45:37,602 --> 00:45:40,402
things, as we might expect.     
And if none, if nothing         

933
00:45:40,471 --> 00:45:43,739
matches then I'll get an empty  
array. If there was an error,   

934
00:45:43,807 --> 00:45:46,775
like maybe my predicate         
had a syntax error I said,      

935
00:45:46,844 --> 00:45:50,646
like any twoots got created     
by, then this is gonna throw.   

936
00:45:50,715 --> 00:45:53,282
And I'll have to catch it and   
figure that out.                

937
00:45:53,350 --> 00:45:55,651
But otherwise it returns        
in array of objects.            

938
00:45:55,720 --> 00:45:58,220
So it's really easy to query    
the database too, and it's      

939
00:45:58,289 --> 00:46:00,823
using SQL to do that search so  
it's super efficient.           

940
00:46:00,891 --> 00:46:04,794
And it's, even large values     
coming back, it's efficient     

941
00:46:04,862 --> 00:46:07,363
about that as well. I can't     
talk about how it does that,    

942
00:46:07,432 --> 00:46:10,032
but it's also very efficient    
even if huge things are,        

943
00:46:10,101 --> 00:46:13,803
are returned. And               
Core Data can do so much more.  

944
00:46:13,872 --> 00:46:15,338
It has great support for        
multithreading,                 

945
00:46:15,406 --> 00:46:17,773
it has a very close             
integration with UITableView,   

946
00:46:17,842 --> 00:46:18,641
as you can imagine.             

947
00:46:18,710 --> 00:46:21,010
You, you know, often might      
want the information from       

948
00:46:21,079 --> 00:46:23,812
the database to appear in a     
table. You can even set it up   

949
00:46:23,881 --> 00:46:27,016
so a table is always showing    
the result of a fetch request,  

950
00:46:27,084 --> 00:46:29,151
even if the database            
changes from underneath.        

951
00:46:29,219 --> 00:46:31,621
It just automatically           
updates the table, and auto,    

952
00:46:31,689 --> 00:46:33,656
you don£t have to do            
anything in your code.          

953
00:46:33,725 --> 00:46:36,358
Just say what fetch request     
you want associated with        

954
00:46:36,427 --> 00:46:39,128
the table. It does              
lots of good databasey,         

955
00:46:39,196 --> 00:46:42,799
things like optimistic locking  
and rolling back changes.       

956
00:46:42,867 --> 00:46:46,468
You can do undo redo            
really easily with this,        

957
00:46:46,537 --> 00:46:49,905
with the Core Data. And so I,   

958
00:46:49,973 --> 00:46:51,874
I can't cover any of that,      
but I just wanted to give you   

959
00:46:51,943 --> 00:46:53,709
a kind of an idea of            
what Core Data can do,          

960
00:46:53,778 --> 00:46:56,645
cuz it's a very powerful        
framework in iOS. So check out  

961
00:46:56,713 --> 00:47:00,316
my last quarter's iTunes U to   
figure out how to do that.      

962
00:47:00,385 --> 00:47:03,452
I do a full demo the whole      
deal. All right, so             

963
00:47:03,521 --> 00:47:06,688
next topic is also something    
I can't talk about this week.   

964
00:47:06,757 --> 00:47:10,559
But I also did a week on this   
the quarter before that.        

965
00:47:10,628 --> 00:47:12,361
So if you go back               
one more iTunes U,              

966
00:47:12,429 --> 00:47:14,997
instead of Core Data that       
quarter I did Cloud Kit,        

967
00:47:15,065 --> 00:47:17,866
and instead of either of them   
this quarter we'£e doing        

968
00:47:17,935 --> 00:47:19,602
the document browser. So        

969
00:47:19,670 --> 00:47:22,137
every quarter I like to spend   
a week on persistence, and      

970
00:47:22,206 --> 00:47:25,374
I kind of do a different thing  
each quarter. This quarter I'm  

971
00:47:25,443 --> 00:47:29,344
doing document, two quarters    
ago I did Cloud Kit. So         

972
00:47:29,413 --> 00:47:32,548
what is Cloud Kit?              
Cloud Kit is a database also,   

973
00:47:32,617 --> 00:47:35,384
in the same way that Core Data  
is, but it's not a SQL          

974
00:47:35,452 --> 00:47:38,253
database. It's a very simple    
database, it just has           

975
00:47:38,322 --> 00:47:40,823
kind of objects and the         
properties in those objects.    

976
00:47:40,892 --> 00:47:43,592
And you can query on them, but  
they're simple queries. And     

977
00:47:43,660 --> 00:47:46,963
relationships between things    
have to be pretty simple and    

978
00:47:47,031 --> 00:47:50,165
straightforward. But            
what's incredible about it is,  

979
00:47:50,234 --> 00:47:53,135
it's on the network. So         
this is a network database, so  

980
00:47:53,204 --> 00:47:56,238
Core Data, you can have your    
database file on the network.   

981
00:47:56,306 --> 00:47:59,007
But when you start accessing    
it, it has to bring the file    

982
00:47:59,076 --> 00:48:01,476
down to your local machine      
Cuz it's a local SQL.           

983
00:48:01,545 --> 00:48:04,046
Database thing                  
whereas Cloud Kit               

984
00:48:04,115 --> 00:48:06,315
actually when you make          
a request to search for         

985
00:48:06,384 --> 00:48:09,351
something, it does it over      
the Internet to iCloud and      

986
00:48:09,419 --> 00:48:12,822
says search that database and   
send the results back. So       

987
00:48:12,890 --> 00:48:17,326
Cloud Kit's API is completely   
asynchronous, right,            

988
00:48:17,395 --> 00:48:19,528
you make requests and then      
you provide a closure, and      

989
00:48:19,597 --> 00:48:22,531
it calls you back later when    
it's got the result. So         

990
00:48:22,600 --> 00:48:25,167
this requires a certain         
thoughtfulness                  

991
00:48:25,236 --> 00:48:27,769
in programming when             
things can take a long          

992
00:48:27,838 --> 00:48:30,472
time like that, okay. You've    
already seen this a little bit  

993
00:48:30,541 --> 00:48:33,475
with multi-threading in your    
homework, hopefully, but        

994
00:48:33,544 --> 00:48:36,578
it's kinda amplified in         
Cloud Kit. Now it's not,        

995
00:48:36,647 --> 00:48:39,180
it's not bad, it just requires  
you to think in a certain way   

996
00:48:39,249 --> 00:48:41,383
as you're programming. So       

997
00:48:41,452 --> 00:48:42,985
the important components        
of Cloud Kit,                   

998
00:48:43,053 --> 00:48:45,454
you got record types,           
that's kind of like classes.    

999
00:48:45,523 --> 00:48:48,357
You've got fields,              
that's like a var in class,     

1000
00:48:48,426 --> 00:48:51,560
record, that's an instance of   
a class. A reference, that's    

1001
00:48:51,629 --> 00:48:55,197
like a pointer to another       
class, you got databases and    

1002
00:48:55,266 --> 00:48:58,033
zones inside databases. You've  
got containers that contain     

1003
00:48:58,102 --> 00:49:01,503
databases. You've got queries,  
that's like a fetch request,    

1004
00:49:01,572 --> 00:49:04,373
a little bit in Core Data.      
It's actually quite similar     

1005
00:49:04,442 --> 00:49:05,774
to a fetch request              
in Core Data. And               

1006
00:49:05,843 --> 00:49:09,244
then you've got subscriptions   
which are a fantastic feature.  

1007
00:49:09,313 --> 00:49:12,747
That's, you make a query, and   
you give it to the server, and  

1008
00:49:12,816 --> 00:49:14,984
you say anytime                 
the database changes,           

1009
00:49:15,052 --> 00:49:17,019
such that this                  
query would change,             

1010
00:49:17,088 --> 00:49:20,222
send me a push notification.    
Do you all know what a push...  

1011
00:49:20,291 --> 00:49:23,592
who knows what a push           
notification is? So             

1012
00:49:23,661 --> 00:49:27,162
not everyone, but most people.  
So a push notification is just  

1013
00:49:27,231 --> 00:49:29,899
something that comes to your    
app, and it'll even wake        

1014
00:49:29,967 --> 00:49:33,002
your app up and say, whoa,      
some information has arrived.   

1015
00:49:33,070 --> 00:49:35,071
And that is one of the          
coolest, if not the coolest,    

1016
00:49:35,139 --> 00:49:37,672
feature in Cloud Kit,           
is that you'll get notified     

1017
00:49:37,741 --> 00:49:39,909
when the database changes in    
a way that you care about.      

1018
00:49:39,977 --> 00:49:42,978
Those are called                
subscriptions. But              

1019
00:49:43,046 --> 00:49:44,646
you're gonna see, I'm gonna     
show you some code for          

1020
00:49:44,715 --> 00:49:47,749
Cloud Kit. It's not like Core   
Data in that it doesn't look    

1021
00:49:47,818 --> 00:49:49,301
like Swift in the code. You've  
got more function calls and     

1022
00:49:49,302 --> 00:49:50,785
as much just                    

1023
00:49:50,854 --> 00:49:54,223
stuff. Now to use Cloud Kit,    
you have to turn on iCloud.     

1024
00:49:54,292 --> 00:49:56,591
And you do this, like a lot of  
things you have to turn on,     

1025
00:49:56,660 --> 00:49:58,660
like push notifications and     
other things,                   

1026
00:49:58,729 --> 00:50:01,797
in the Capabilities section     
of your project settings.       

1027
00:50:01,865 --> 00:50:03,832
So you're gonna go there        
to Capabilities, and            

1028
00:50:03,901 --> 00:50:07,569
you're gonna flip this          
switch for iCloud ON. And       

1029
00:50:07,638 --> 00:50:10,338
then you're gonna turn on this  
little Cloud Kit switch down    

1030
00:50:10,407 --> 00:50:12,808
here, and that's gonna          
enable that capability for      

1031
00:50:12,877 --> 00:50:14,977
you to use Cloud Kit.           
If you don't turn this on,      

1032
00:50:15,045 --> 00:50:17,212
you won't be able to use it.    
And when you do that,           

1033
00:50:17,281 --> 00:50:19,848
there's gonna be this little    
button down at the bottom       

1034
00:50:19,917 --> 00:50:22,651
called Cloud Kit Dashboard.     
This Cloud Kit Dashboard,       

1035
00:50:22,720 --> 00:50:25,253
let's press it and              
see what it looks like.         

1036
00:50:25,322 --> 00:50:27,489
It's gonna go to this place on  
the Web, where it's gonna show  

1037
00:50:27,558 --> 00:50:30,726
you your database schema.       
So all your record types,       

1038
00:50:30,795 --> 00:50:33,061
and all the little fields       
in it, not just that, but       

1039
00:50:33,130 --> 00:50:36,565
the actual data. Which it's     
not that useful once you ship   

1040
00:50:36,634 --> 00:50:38,767
your app because you're gonna   
have thousands of users         

1041
00:50:38,835 --> 00:50:40,869
generating so much data         
you can't even look at it.      

1042
00:50:40,938 --> 00:50:43,005
But in development,             
it's really great,              

1043
00:50:43,074 --> 00:50:45,708
because you create a object     
and you can go look at it and   

1044
00:50:45,776 --> 00:50:48,410
make sure it got in there and   
it's got the right data or      

1045
00:50:48,479 --> 00:50:53,014
whatever. So this dashboard is  
how you kind of work on your    

1046
00:50:53,083 --> 00:50:57,519
schema. It's not quite          
like the Core Data schema       

1047
00:50:57,588 --> 00:51:02,057
editor thing. Because in Cloud  
Kit, different than Core Data,  

1048
00:51:02,126 --> 00:51:03,859
it builds the schema            
as you go.                      

1049
00:51:03,927 --> 00:51:07,729
As soon as you, if you say      
create an object of this name,  

1050
00:51:07,798 --> 00:51:11,433
it'll just go create it. It's,  
it's gonna do it on the fly,    

1051
00:51:11,502 --> 00:51:14,269
you don't have to go and        
pre-build your schema like you  

1052
00:51:14,338 --> 00:51:17,473
do in Core Data. That's what    
this is talking about, dynamic  

1053
00:51:17,541 --> 00:51:19,842
schema creation. And this only  
works during development,       

1054
00:51:19,911 --> 00:51:22,277
obviously. Once you ship        
it to your users, then          

1055
00:51:22,346 --> 00:51:26,548
it's not gonna create classes   
and fields on the fly as you    

1056
00:51:26,616 --> 00:51:28,717
access them. But you're in      
development, it's really nice,  

1057
00:51:28,786 --> 00:51:31,353
it's really easy, to just       
start writing code, and have    

1058
00:51:31,422 --> 00:51:34,990
it start building the database  
that would match that code.     

1059
00:51:35,059 --> 00:51:36,725
All right, so here's what       
the code looks like. You're     

1060
00:51:36,794 --> 00:51:39,594
gonna see it doesn't look       
like as nice as Core Data.      

1061
00:51:39,663 --> 00:51:42,330
So you have to get a database,  
so usually,                     

1062
00:51:42,399 --> 00:51:45,267
you're gonna use the public or  
private cloud database.         

1063
00:51:45,336 --> 00:51:48,737
Then to create a tweet, you     
see you're gonna say CKRecord,  

1064
00:51:48,805 --> 00:51:51,907
CK is Cloud Kit. CKRecord with  
the name Tweet which would      

1065
00:51:51,975 --> 00:51:55,077
automatically add that table    
to the database if it didn't    

1066
00:51:55,146 --> 00:51:58,180
exist. Then you're gonna        
say tweet subquote              

1067
00:51:58,249 --> 00:52:01,750
text = the text. And then to    
have a tweeter you have to say  

1068
00:52:01,819 --> 00:52:05,520
CKRecord TwitterUser. And       
then say tweet sub tweeter =    

1069
00:52:05,589 --> 00:52:10,058
CKReference to record tweeter   
with the action delete this     

1070
00:52:10,127 --> 00:52:12,861
thing if the thing it's in      
gets deleted. So you see,       

1071
00:52:12,930 --> 00:52:14,530
it's more verbose and not,      

1072
00:52:14,598 --> 00:52:18,233
doesn't look like Swift, to     
be doing all this stuff. And    

1073
00:52:18,302 --> 00:52:20,802
of course things like saving    
are asynchronous, right.        

1074
00:52:20,871 --> 00:52:22,938
So here I wanna save this       
tweet in the database.          

1075
00:52:23,007 --> 00:52:25,874
Well, it's going to, I have     
to provide this closure,        

1076
00:52:25,943 --> 00:52:28,477
and it's gonna call me          
back once it's finished or      

1077
00:52:28,545 --> 00:52:32,480
if there were an error. Now     
this networking programming,    

1078
00:52:32,549 --> 00:52:35,350
always a lot of error           
handling. And so                

1079
00:52:35,419 --> 00:52:37,753
if you guys haven't done        
networking programming,         

1080
00:52:37,822 --> 00:52:40,455
get used to it, there are 29    
different errors in Cloud Kit   

1081
00:52:40,524 --> 00:52:44,459
error. And not all of them can  
happen on every operation, but  

1082
00:52:44,528 --> 00:52:47,796
a lot of them can. For          
example, I've shown the error   

1083
00:52:47,865 --> 00:52:50,598
here NotAuthenticated.          
Because since it's Cloud Kit,   

1084
00:52:50,667 --> 00:52:53,068
if the user's not logged in     
to iCloud on their device,      

1085
00:52:53,136 --> 00:52:55,070
then it's not going to          
know who they are, so           

1086
00:52:55,139 --> 00:52:57,406
it's not gonna work.            
So you could get that error.    

1087
00:52:57,475 --> 00:53:00,842
You can get network timeouts,   
all kinds of stuff. So          

1088
00:53:00,911 --> 00:53:04,246
that's just a different way of  
program, you have to kind of    

1089
00:53:04,315 --> 00:53:07,349
get used to it,                 
this asynchronous programming.  

1090
00:53:07,418 --> 00:53:10,385
Here's what a query looks       
like. This is the analog of     

1091
00:53:10,454 --> 00:53:14,089
the fetch request.              
You still use NSPredicate. So   

1092
00:53:14,158 --> 00:53:17,259
like text contains              
some searchString or            

1093
00:53:17,328 --> 00:53:21,329
whatever. But the predicates    
can't be quite as complicated   

1094
00:53:21,398 --> 00:53:24,399
as in Core Data. They have      
to be fairly straightforward    

1095
00:53:24,468 --> 00:53:26,635
predicates. But                 
then you create a CKQuery,      

1096
00:53:26,704 --> 00:53:29,137
which is a Cloud Kit query,     
and then you say perform, and   

1097
00:53:29,206 --> 00:53:32,173
of course it's asynchronous.    
So you provide a closure, and   

1098
00:53:32,242 --> 00:53:35,511
it calls you back with the      
results of doing that query.    

1099
00:53:35,579 --> 00:53:38,180
So that's what querying,        
querying looks like.            

1100
00:53:38,249 --> 00:53:41,717
Again, pretty simple,           
but asynchronous and            

1101
00:53:41,785 --> 00:53:45,353
not as powerful as Core Data.   
Standing queries or             

1102
00:53:45,422 --> 00:53:48,356
subscriptions, I can't really   
show you what that code looks   

1103
00:53:48,425 --> 00:53:51,526
like because I haven't taught   
you push notifications.         

1104
00:53:51,595 --> 00:53:53,895
Push notifications              
are not that difficult.         

1105
00:53:53,964 --> 00:53:57,599
There's a whole framework for   
it called UserNotifications.    

1106
00:53:57,668 --> 00:53:59,668
But it doesn't make sense for   
me to show you what it          

1107
00:53:59,737 --> 00:54:01,804
looks like when I               
haven't taught you that.        

1108
00:54:01,872 --> 00:54:04,806
So we'll put that off til       
later. Maybe I'll try and show  

1109
00:54:04,875 --> 00:54:08,543
an example of a Cloud Kit,      
push notification happening,    

1110
00:54:08,612 --> 00:54:13,248
when we cover that.             
All right, now, next topic.     

1111
00:54:13,316 --> 00:54:16,885
So this is the topic that I     
am gonna spend this week on,    

1112
00:54:16,954 --> 00:54:19,555
which is document-based apps.   
So                              

1113
00:54:19,623 --> 00:54:23,325
this is persistence when the    
thing that you're persisting    

1114
00:54:23,394 --> 00:54:26,561
is perceived by                 
the user as a document.         

1115
00:54:26,630 --> 00:54:30,532
For example, emoji art.         
I create a beautiful emoji art  

1116
00:54:30,601 --> 00:54:34,903
document, put my ghost and      
my bike in there, my bees.      

1117
00:54:34,972 --> 00:54:37,972
And then I wanted to save like  
a document, and then the user   

1118
00:54:38,041 --> 00:54:41,042
is gonna go create a different  
one with some other image and   

1119
00:54:41,111 --> 00:54:42,477
some other stuff in there.      

1120
00:54:42,546 --> 00:54:44,045
And they wanna save that        
as a different document.        

1121
00:54:44,114 --> 00:54:45,914
So they, you see how they       
viewed them as documents.       

1122
00:54:45,982 --> 00:54:47,849
Same thing with your            
image gallery homework.         

1123
00:54:47,918 --> 00:54:49,751
You have a gallery of           
images that you built, and      

1124
00:54:49,819 --> 00:54:52,287
then maybe you wanna have       
a different gallery of images   

1125
00:54:52,356 --> 00:54:52,954
that are related in             

1126
00:54:53,023 --> 00:54:56,191
some other way. Those           
are perceived as documents. So  

1127
00:54:56,260 --> 00:55:00,728
we're gonna talk about a        
mechanism that iOS API has for  

1128
00:55:00,797 --> 00:55:04,632
storing things of document      
that is fantastic. It takes     

1129
00:55:04,701 --> 00:55:07,903
care of absolutely everything   
you wanna do with a document,   

1130
00:55:07,971 --> 00:55:08,703
and you have to hard,           

1131
00:55:08,772 --> 00:55:12,841
do hardly any work to make it   
work. All you have to do is     

1132
00:55:12,909 --> 00:55:16,177
actually convert your model     
into a data and back.           

1133
00:55:16,246 --> 00:55:20,381
And that's it, and it manages   
absolutely everything else. So  

1134
00:55:20,450 --> 00:55:22,050
when I say it manages           
everything else,                

1135
00:55:22,118 --> 00:55:26,754
what do I mean? Well, opening,  
writing, reading, closing       

1136
00:55:26,823 --> 00:55:31,126
document files asynchronously   
is all handled by UIDocument.   

1137
00:55:31,195 --> 00:55:36,297
Now why do I want my documents  
opened, say, asynchronously?    

1138
00:55:36,366 --> 00:55:39,534
Why do I care? My documents     
aren't big, it's not gonna      

1139
00:55:39,603 --> 00:55:41,269
take that much time to write    
them to the file system,        

1140
00:55:41,338 --> 00:55:45,840
who cares? Well, UIDocument     
supports saving your files in   

1141
00:55:45,909 --> 00:55:51,646
iCloud drive. On the network,   
and that could be slower. So,   

1142
00:55:51,715 --> 00:55:54,415
if you had to write the code    
to save them to iCloud drive,   

1143
00:55:54,484 --> 00:55:57,185
you'd be very sad indeed,       
because you'd have to do all    

1144
00:55:57,254 --> 00:56:00,054
that networking code to figure  
out how did I get this thing    

1145
00:56:00,123 --> 00:56:02,523
over the network? Did it fail?  
Is it the network?              

1146
00:56:02,592 --> 00:56:04,292
Whereas, this way               
you use UIDocument,             

1147
00:56:04,361 --> 00:56:07,495
you just say save. It'll just   
call you back when it's done.   

1148
00:56:07,564 --> 00:56:09,465
It's all asynchronous,          
it's awesome.                   

1149
00:56:11,034 --> 00:56:14,135
It also will auto save          
your document. And, again,      

1150
00:56:14,204 --> 00:56:16,871
I told you one of the ways to   
get a context for your core     

1151
00:56:16,940 --> 00:56:19,841
data is to create a UI managed  
documents, it's called,         

1152
00:56:19,910 --> 00:56:23,044
which is a subclass UIDocument  
for core data databases, and    

1153
00:56:23,113 --> 00:56:25,547
it will autosave it. Well the   
same thing happened for yours.  

1154
00:56:25,616 --> 00:56:27,682
Your documents can just         
be automatically saved,         

1155
00:56:27,751 --> 00:56:29,651
you don't even have             
to save them. And               

1156
00:56:29,720 --> 00:56:32,487
the most important thing        
about UIDocument is that        

1157
00:56:32,556 --> 00:56:36,391
it integrates with iOS          
11's Files app, and             

1158
00:56:36,460 --> 00:56:38,059
the document browser.           
And we're gonna see,            

1159
00:56:38,128 --> 00:56:41,029
if we get to it today,          
which hopefully we will,        

1160
00:56:41,098 --> 00:56:44,666
what that means cuz it means    
a lot, it's very powerful. So   

1161
00:56:44,735 --> 00:56:47,969
what do you need to do          
to make UIDocument work?        

1162
00:56:48,038 --> 00:56:51,240
You want to have UIDocument.    
Well I'm gonna assume you       

1163
00:56:51,308 --> 00:56:54,275
already have an MVC that        
displays your document and      

1164
00:56:54,344 --> 00:56:57,546
that it has some var or vars    
that are its model, right.      

1165
00:56:57,615 --> 00:56:59,447
This is MVC,                    
of course it's got a model.     

1166
00:56:59,516 --> 00:57:02,483
So like in emoji art we         
don't have our model yet        

1167
00:57:02,552 --> 00:57:05,887
in emoji art, but imagine I     
had some var of type emoji      

1168
00:57:05,956 --> 00:57:09,524
art, which was the model for    
what I'm showing. It would      

1169
00:57:09,593 --> 00:57:12,427
have the URL of the image, and  
it would have all the emoji,    

1170
00:57:12,495 --> 00:57:15,163
and where they were, and        
the size they were, right?      

1171
00:57:15,232 --> 00:57:17,032
That would be                   
the model of the thing.         

1172
00:57:17,100 --> 00:57:20,201
So I'm gonna assume I start     
there. So all you need to do    

1173
00:57:20,270 --> 00:57:23,572
to turn your app into working   
with UIDocument is to be able   

1174
00:57:23,640 --> 00:57:28,176
to convert that model to a      
data, and convert from a data   

1175
00:57:28,245 --> 00:57:30,312
back to the model.              
Well, earlier in this lecture,  

1176
00:57:30,380 --> 00:57:32,447
didn't I just show you          
exactly how to do that with     

1177
00:57:32,516 --> 00:57:36,017
the archiver? Really easy.      
So you could use JSON format    

1178
00:57:36,086 --> 00:57:38,654
as the file format of           
your document, and              

1179
00:57:38,722 --> 00:57:42,023
just use the archiving to turn  
your model back and forth       

1180
00:57:42,092 --> 00:57:44,859
between the data, and that's    
really all you have to do.      

1181
00:57:44,928 --> 00:57:47,095
The only other thing            
you might wanna do Is           

1182
00:57:47,163 --> 00:57:49,998
tell the UIDocument whenever    
your document changes,          

1183
00:57:50,067 --> 00:57:52,568
like if you drag a new          
emoji in or whatever, and       

1184
00:57:52,636 --> 00:57:54,903
then it'll autosave.            
Cuz you have to tell it that,   

1185
00:57:54,972 --> 00:57:56,871
otherwise it doesn't            
know when to autosave.          

1186
00:57:56,940 --> 00:57:59,207
But that is literally           
called one function,            

1187
00:57:59,275 --> 00:58:03,010
my document changed, and it'll  
figure it out from there.       

1188
00:58:03,079 --> 00:58:05,213
That's it, that's all you have  
to do to make UIDocument work.  

1189
00:58:05,282 --> 00:58:09,317
Really implement two methods,   
get and set my model as         

1190
00:58:09,385 --> 00:58:14,489
a data. So how do we do that?   
We subclass UIDocument and      

1191
00:58:14,558 --> 00:58:17,592
we override two methods, the    
one that creates the data and   

1192
00:58:17,661 --> 00:58:21,229
one gets our model from the     
data. Now we're almost always   

1193
00:58:21,298 --> 00:58:25,133
going to want to add a var      
in our UIDocument subclass,     

1194
00:58:25,202 --> 00:58:28,469
which is the model. The model   
that we're going to be          

1195
00:58:28,538 --> 00:58:30,372
the converting to and           
from a data. So,                

1196
00:58:30,440 --> 00:58:32,307
here if I had                   
an EmojiArtDocument             

1197
00:58:32,376 --> 00:58:35,676
subclassing UIdocument, I'm     
adding a var called EmojiArt,   

1198
00:58:35,745 --> 00:58:36,812
which is of type EmojiArt.      

1199
00:58:36,880 --> 00:58:40,115
That's presumably the type      
of the model that               

1200
00:58:40,184 --> 00:58:44,453
I have in my EmojiArtDocument.  
Now there are other methods     

1201
00:58:44,521 --> 00:58:46,721
you can override in UIDocument  
that do some things.            

1202
00:58:46,790 --> 00:58:48,857
I'll even talk about one of     
them towards the end. But       

1203
00:58:48,926 --> 00:58:52,427
the main two things you         
wanna do is the reading and     

1204
00:58:52,495 --> 00:58:54,729
writing of the data. And the    
only thing you have to do to    

1205
00:58:54,798 --> 00:58:59,401
create the UIDocument is        
specify the URL it's at.        

1206
00:58:59,470 --> 00:59:03,305
So the only initializer         
that exists for                 

1207
00:59:03,373 --> 00:59:05,473
UIDocument, it                  
takes one argument,             

1208
00:59:05,542 --> 00:59:08,776
as you can see it in yellow     
right there, fileURL, and       

1209
00:59:08,845 --> 00:59:12,146
that is gonna be the URL        
of the document. Now I'm        

1210
00:59:12,215 --> 00:59:15,583
gonna show you later that this  
URL might be given to you and   

1211
00:59:15,652 --> 00:59:19,921
might be an iCloud drive,       
and you might not even care.    

1212
00:59:19,990 --> 00:59:23,424
But you also could, of course,  
create a URL somewhere          

1213
00:59:23,493 --> 00:59:26,494
presumably in the documents     
directory of your sandbox, and  

1214
00:59:26,563 --> 00:59:30,832
create your own document if     
you want. But actually, in iOS  

1215
00:59:30,901 --> 00:59:35,603
11, usually we let the files    
app mechanism give us the URL.  

1216
00:59:35,672 --> 00:59:37,806
The user goes to where they     
want the file to be, and        

1217
00:59:37,874 --> 00:59:40,141
they say create document,       
and it gives us URL, and        

1218
00:59:40,210 --> 00:59:42,244
we just call this to            
create our UIDocument.          

1219
00:59:43,847 --> 00:59:46,014
Now once we've created          
our UIDocument,                 

1220
00:59:46,083 --> 00:59:48,783
we're gonna set that var        
that I defined at the top of    

1221
00:59:48,852 --> 00:59:51,653
the screen there. We're gonna   
set that model in there and     

1222
00:59:51,721 --> 00:59:53,554
then UIDocument's gonna         
take it from there.             

1223
00:59:53,623 --> 00:59:54,889
It's gonna read and             
write the file and              

1224
00:59:54,958 --> 00:59:57,992
everything. All right, so how   
about doing this conversion     

1225
00:59:58,061 --> 01:00:01,830
from emojiArt to data and       
from data to emojiArt. So       

1226
01:00:01,899 --> 01:00:04,599
here's the two methods. This    
is the one that converts your   

1227
01:00:04,668 --> 01:00:08,570
model into a data, it's called  
contents for type, okay.        

1228
01:00:08,639 --> 01:00:10,839
It does throw, You could        
throw. If you have a problem    

1229
01:00:10,907 --> 01:00:13,507
converting your emojiArt to     
a Data, you could throw. And    

1230
01:00:13,576 --> 01:00:17,212
I'll show you where that thing  
gets thrown to. And notice it   

1231
01:00:17,280 --> 01:00:20,215
returns an Any. You would       
think that would return a Data  

1232
01:00:20,284 --> 01:00:22,450
right there, but it returns an  
Any because you can actually    

1233
01:00:22,519 --> 01:00:26,754
also represent your document    
as a directory full of files.   

1234
01:00:26,823 --> 01:00:29,257
That's called a FileWrapper.    
But                             

1235
01:00:29,326 --> 01:00:32,160
we're just gonna talk about     
the Data way of doing it.       

1236
01:00:32,229 --> 01:00:33,762
If you wanna do the             
FileWrapper way, you'll have    

1237
01:00:33,831 --> 01:00:35,730
to look up the documentation    
for file wrappers.              

1238
01:00:35,799 --> 01:00:37,532
It's not that hard,             
but it's a little more          

1239
01:00:37,601 --> 01:00:40,368
complicated than just turning   
it into a Data blob. And        

1240
01:00:40,437 --> 01:00:42,738
so how am I gonna               
implement this method?          

1241
01:00:42,806 --> 01:00:44,739
Real easy, I'm gonna use        
that archiving stuff, and       

1242
01:00:44,808 --> 01:00:47,241
use a JSON encoder or           
something right here, and       

1243
01:00:47,310 --> 01:00:50,411
create a Data object. And       
I just return it, that's it.    

1244
01:00:50,480 --> 01:00:53,748
So this often is a one liner,   
this contents for type. Now     

1245
01:00:53,817 --> 01:00:56,985
that type that you see right    
there, yeah I already said you  

1246
01:00:57,053 --> 01:00:59,387
could throw there. So the type  
that's passed along there,      

1247
01:00:59,456 --> 01:01:03,658
that's a UTI, a universal       
type identifier. And            

1248
01:01:03,727 --> 01:01:05,493
I'm gonna talk a little         
bit about what that is          

1249
01:01:05,562 --> 01:01:09,464
in a few slides.                
This is not a type like .jpeg.  

1250
01:01:09,532 --> 01:01:12,434
This is a type like             
public.json, which would        

1251
01:01:12,502 --> 01:01:16,538
be a JSON file, or public.img,  
it's an image file. That's      

1252
01:01:16,607 --> 01:01:18,573
the kind of thing that's        
gonna be in that type name.     

1253
01:01:18,642 --> 01:01:21,509
Usually you don't care because  
usually your UIDocument only    

1254
01:01:21,578 --> 01:01:25,013
opens one kind of file anyway,  
like an emojiArt document, so   

1255
01:01:25,082 --> 01:01:27,215
you don't even care what        
that type is. But you might     

1256
01:01:27,284 --> 01:01:30,118
be a UIDocument that can be     
in different formats and then   

1257
01:01:30,186 --> 01:01:33,755
maybe you care. Alright, how    
about the other way around?     

1258
01:01:33,824 --> 01:01:35,890
You've got a data,              
that's handed to you,           

1259
01:01:35,959 --> 01:01:37,792
you gotta turn                  
into your model.                

1260
01:01:37,861 --> 01:01:42,229
Again you're probably going     
to use that JSON Decoder, and   

1261
01:01:42,298 --> 01:01:47,001
take the data and turn it back  
into an emoji art. And again,   

1262
01:01:47,070 --> 01:01:50,738
it's got the types there, load  
from contents of type, that's   

1263
01:01:50,807 --> 01:01:54,041
UTI. This one throws as well.   
This one you're more likely to  

1264
01:01:54,110 --> 01:01:57,579
throw, because here you're      
being given a JSON thing or     

1265
01:01:57,647 --> 01:02:00,749
a Data blob, and you're         
turning into EmojiArt. It       

1266
01:02:00,817 --> 01:02:03,385
might be corrupted, it might    
not be in the right format,     

1267
01:02:03,453 --> 01:02:07,021
something's wrong with it,      
so you might throw here.        

1268
01:02:07,090 --> 01:02:09,758
And, in fact, that's all you    
need to do is implement those   

1269
01:02:09,826 --> 01:02:12,294
two methods. And now you        
can use all the methods in      

1270
01:02:12,362 --> 01:02:15,863
UIDocument like open,           
which opens your documents.     

1271
01:02:15,932 --> 01:02:19,501
And it's asynchronous, so you   
provide it a closure there,     

1272
01:02:19,569 --> 01:02:21,536
and it even tells you whether   
you successfully did it or      

1273
01:02:21,605 --> 01:02:24,205
not. If it doesn't              
successfully open it, you're    

1274
01:02:24,273 --> 01:02:26,241
gonna be looking at this thing  
called documentState, and       

1275
01:02:26,309 --> 01:02:28,676
I'm gonna talk about that       
in a second, all right.         

1276
01:02:28,745 --> 01:02:30,611
So that's how you open          
a document. And you do have to  

1277
01:02:30,680 --> 01:02:33,447
open your UIDocument before     
you can use it, of course,      

1278
01:02:33,516 --> 01:02:35,349
because UIDocument wants        
to go and get the file,         

1279
01:02:35,418 --> 01:02:36,851
and get the data,               
and stuff like that.            

1280
01:02:36,920 --> 01:02:40,055
Call the method that converts   
it into an emoji art or         

1281
01:02:40,123 --> 01:02:43,358
whatever, but                   
you do have to open your file.  

1282
01:02:43,427 --> 01:02:46,627
You can save your file          
explicitly or you can just do   

1283
01:02:46,696 --> 01:02:49,264
auto saving. If you do auto     
saving, this is the method you  

1284
01:02:49,332 --> 01:02:52,968
have to call to tell your       
UIDocument I've changed.        

1285
01:02:53,036 --> 01:02:57,571
UpdateChangeCount(.done).       
Another way, by the way, to do  

1286
01:02:57,640 --> 01:03:01,709
this is to use the undoManager  
of UIDocument. Unfortunately,   

1287
01:03:01,778 --> 01:03:04,112
I don't have time to teach      
you about doing undo.           

1288
01:03:04,181 --> 01:03:05,180
undoManager is a really         

1289
01:03:05,248 --> 01:03:08,049
cool little class where every   
time you do an operation,       

1290
01:03:08,118 --> 01:03:09,784
like drag a new emoji in or     

1291
01:03:09,853 --> 01:03:12,186
resize it,                      
you go to the undoManager and   

1292
01:03:12,255 --> 01:03:15,056
say, I just did this operation  
and here's a closure for        

1293
01:03:15,125 --> 01:03:20,127
how to undo it. And then, it    
automatically does Undo/Redo,   

1294
01:03:20,196 --> 01:03:22,464
and just pulls those closures   
out so you can undo and         

1295
01:03:22,532 --> 01:03:25,299
then redo, go back and forth.   
And of course, if you use       

1296
01:03:25,368 --> 01:03:28,670
the UIDocument's undoManager    
to do that, then it will know   

1297
01:03:28,738 --> 01:03:31,739
that the document has changed   
when you do these Undo and      

1298
01:03:31,808 --> 01:03:37,045
Redo things. So that's another  
way to use the undoManager.     

1299
01:03:37,114 --> 01:03:39,780
If you wanna explicitly save,   
there is a save.                

1300
01:03:39,849 --> 01:03:42,383
The save one is not like open,  
it actually has a couple        

1301
01:03:42,452 --> 01:03:46,755
arguments here. The reason      
you have save to URL is for     

1302
01:03:46,823 --> 01:03:50,291
save as. Because of course      
a document knows its own URL,   

1303
01:03:50,360 --> 01:03:52,527
that was specified in           
its initialize, or              

1304
01:03:52,595 --> 01:03:56,464
the file URL. So save to URL    
allows you to save it off to    

1305
01:03:56,532 --> 01:03:59,100
another URL like save as.       
And then that for               

1306
01:03:59,169 --> 01:04:01,703
document save operation,        
unfortunately when you save,    

1307
01:04:01,772 --> 01:04:04,272
you have to know whether        
this is the initial document    

1308
01:04:04,341 --> 01:04:07,274
creation save Or whether        
it's a subsequent safe.         

1309
01:04:07,343 --> 01:04:09,010
You have to tell                
the system that.                

1310
01:04:09,079 --> 01:04:11,612
I'm not sure why it makes you   
do that versus it going out     

1311
01:04:11,681 --> 01:04:14,382
and figuring it out, I think    
it's just for flexibility.      

1312
01:04:14,451 --> 01:04:17,585
Cuz it can save into so many    
different kinds of containers.  

1313
01:04:17,654 --> 01:04:21,055
iCloud drive, your local file   
system, it can even save into   

1314
01:04:21,124 --> 01:04:25,126
things like Box. So maybe some  
of them don't allow it to ask   

1315
01:04:25,194 --> 01:04:28,630
the question of whether the     
file exists or not, I'm not     

1316
01:04:28,698 --> 01:04:31,899
exactly sure why it does that.  
But when you say it,            

1317
01:04:31,968 --> 01:04:35,636
you do have to know whether     
you're creating it or not.      

1318
01:04:35,705 --> 01:04:37,404
When you're done                
with your document,             

1319
01:04:37,473 --> 01:04:40,408
you're gonna want to close it.  
Of course, the big thing this   

1320
01:04:40,477 --> 01:04:43,545
does is save it, if it's got    
any outstanding changes.        

1321
01:04:43,613 --> 01:04:46,381
And again, if it fails closing  
it, you're gonna have this      

1322
01:04:46,450 --> 01:04:48,950
document state thing. So        
what is, what I keep saying,    

1323
01:04:49,019 --> 01:04:50,852
look at the document            
state if things fail,           

1324
01:04:50,921 --> 01:04:53,822
what is that about? Well,       
let's look at the document      

1325
01:04:53,890 --> 01:04:56,324
state, the document state       
is a var in UIDocument.         

1326
01:04:56,393 --> 01:04:58,827
You can look at it and          
see how your document's doing.  

1327
01:04:58,895 --> 01:05:01,829
Here's some of the values,      
normal, that means your         

1328
01:05:01,898 --> 01:05:05,166
document is ready to use. Just  
do whatever you want with it,   

1329
01:05:05,234 --> 01:05:07,601
that's the normal state.        
There's also closed,            

1330
01:05:07,670 --> 01:05:10,838
that means either you haven't   
opened it or you tried to open  

1331
01:05:10,907 --> 01:05:13,808
it and it failed, and it's      
still in the closed state.      

1332
01:05:13,877 --> 01:05:18,279
There's savingError, which      
is you tried to save it and     

1333
01:05:18,348 --> 01:05:22,183
it failed. There's also         
editingDisabled, and that is    

1334
01:05:22,251 --> 01:05:25,586
a method on UIDocument,         
which is disable editing.       

1335
01:05:25,655 --> 01:05:28,023
And why would you ever want     
to disable editing? Well, for   

1336
01:05:28,091 --> 01:05:30,958
example, the core data          
document, UIManagedDocument.    

1337
01:05:31,027 --> 01:05:33,962
It disables editing when        
it's doing some sort of         

1338
01:05:34,031 --> 01:05:36,865
a SQL operation to update       
the database. Now it            

1339
01:05:36,933 --> 01:05:40,068
only happens for a microsecond  
that it's disabled.             

1340
01:05:40,136 --> 01:05:43,071
But essentially when you set    
editingDisabled as the state    

1341
01:05:43,139 --> 01:05:46,040
of your document. You just      
would not want to allow users   

1342
01:05:46,109 --> 01:05:48,342
to drag new emoji in,           
or resize anything.             

1343
01:05:48,411 --> 01:05:50,945
Not really an issue in          
something like emoji art,       

1344
01:05:51,014 --> 01:05:53,981
where it's very simple. But     
it can be an issue in the core  

1345
01:05:54,050 --> 01:05:57,518
data, or some other more        
complicated storage mechanism.  

1346
01:05:57,587 --> 01:05:59,620
Then there's                    
the progressAvailable state.    

1347
01:05:59,689 --> 01:06:02,223
That means you did              
open on a document, and         

1348
01:06:02,292 --> 01:06:06,027
the document is huge, and it's  
downloading it from iCloud or   

1349
01:06:06,096 --> 01:06:09,163
something. And this will        
tell you that progress,         

1350
01:06:09,232 --> 01:06:11,666
it will be the progress         
bar in the UIDocument,          

1351
01:06:11,734 --> 01:06:13,434
will tell you how               
far along it is.                

1352
01:06:13,503 --> 01:06:16,604
And it will stay in this state  
until it's fully downloaded,    

1353
01:06:16,673 --> 01:06:21,409
and then it will move to open,  
or normal rather. And finally,  

1354
01:06:21,478 --> 01:06:24,345
there's inConflict, which       
is a very fascinating one.      

1355
01:06:24,413 --> 01:06:27,915
Since the document can be       
stored in a network container,  

1356
01:06:27,984 --> 01:06:31,352
it might get saved somewhere    
that had network access at      

1357
01:06:31,421 --> 01:06:34,255
the time. And then start        
editing in another place that   

1358
01:06:34,324 --> 01:06:37,325
didn't have network access, or  
vice versa. Resulting in two    

1359
01:06:37,393 --> 01:06:40,694
versions of the app finally     
getting saved up to iCloud.     

1360
01:06:40,763 --> 01:06:43,931
And now you have two versions   
that might be conflicting, and  

1361
01:06:44,000 --> 01:06:45,299
that's what this is about.      

1362
01:06:45,368 --> 01:06:48,536
Now, you're not gonna deal      
with this in your app.          

1363
01:06:48,605 --> 01:06:51,039
You're probably gonna take the  
default behavior, which is,     

1364
01:06:51,108 --> 01:06:53,140
it uses the one with            
the most recent file date.      

1365
01:06:53,209 --> 01:06:56,544
Whichever one was written       
most recently, it uses. But     

1366
01:06:56,613 --> 01:06:59,113
if you want to resolve the      
difference, and you want to     

1367
01:06:59,182 --> 01:07:01,950
notice this and resolve it,     
you can use this NSFileVersion  

1368
01:07:02,018 --> 01:07:05,052
static method here. And get     
all the different versions,     

1369
01:07:05,121 --> 01:07:07,088
and look at                     
the differences of them.        

1370
01:07:07,157 --> 01:07:09,524
And maybe offer the user        
some choices, whatever,         

1371
01:07:09,592 --> 01:07:12,260
that'd be up to you.            
But for things like emoji art,  

1372
01:07:12,328 --> 01:07:15,396
you're probably fine with       
just always taking the latest   

1373
01:07:15,465 --> 01:07:17,932
version, whichever              
one was saved latest.           

1374
01:07:19,869 --> 01:07:23,304
DocumentState as var can also   
be observed in the same way     

1375
01:07:23,372 --> 01:07:26,674
that the keyboard observing     
can happen. Remember, I told    

1376
01:07:26,742 --> 01:07:28,943
you that there was a way you    
could like tell the system,     

1377
01:07:29,012 --> 01:07:31,512
hey, if the keyboard comes up,  
tell me about it, right?        

1378
01:07:31,581 --> 01:07:34,315
That's called a notification,   
same thing here. You can say,   

1379
01:07:34,384 --> 01:07:36,650
hey, if my document state       
changes, tell me about it,      

1380
01:07:36,719 --> 01:07:39,220
and it would tell you that.     
I'm going to tell you how       

1381
01:07:39,289 --> 01:07:42,223
to do this next week when we    
talk about notifications,       

1382
01:07:42,292 --> 01:07:45,727
and I'll mention document       
state and keyboard. And show    

1383
01:07:45,795 --> 01:07:51,232
you what a code looks like to   
watch your document state.      

1384
01:07:51,301 --> 01:07:54,802
Finally I'm gonna talk about    
a cool little extra method you  

1385
01:07:54,871 --> 01:07:57,672
can override in UIDocument      
to put a thumbnail image.       

1386
01:07:57,740 --> 01:08:01,742
Instead of your documents       
icon. By default,               

1387
01:08:01,811 --> 01:08:04,244
when you look at your           
documents in the files app or   

1388
01:08:04,313 --> 01:08:07,749
whatever, they'll have icons,   
right? Whatever the file type   

1389
01:08:07,817 --> 01:08:10,518
icon, the jpg file icon,        
whatever that is. Or            

1390
01:08:10,587 --> 01:08:13,821
if you have an emoji art type   
of file, which we are gonna     

1391
01:08:13,889 --> 01:08:18,059
talk about, on Wednesday,       
it would show that icon.        

1392
01:08:18,127 --> 01:08:19,494
But you can also say,           

1393
01:08:19,563 --> 01:08:22,563
when the user sees my           
file in the file system,        

1394
01:08:22,632 --> 01:08:26,601
actually use this thumbnail     
image of it as its icon.        

1395
01:08:26,670 --> 01:08:29,003
This is a really powerful       
way to make it easier for       

1396
01:08:29,072 --> 01:08:31,305
users to find which             
document they want.             

1397
01:08:31,374 --> 01:08:34,108
Because imagine emoji art,      
you do some nice art, and       

1398
01:08:34,177 --> 01:08:37,278
it makes a little thumbnail of  
it. So you can actually see     

1399
01:08:37,347 --> 01:08:39,947
the document before you         
open it in the file system,     

1400
01:08:40,016 --> 01:08:42,883
it's like the icon of           
the document. And to do that,   

1401
01:08:42,952 --> 01:08:46,287
all you have to do is override  
this UIDocument method,         

1402
01:08:46,356 --> 01:08:48,856
called File Attributes          
to Write to URL for             

1403
01:08:48,925 --> 01:08:52,660
Operation. This is normally     
just going to return            

1404
01:08:52,729 --> 01:08:56,531
a dictionary of the file        
attributes like, is this file   

1405
01:08:56,599 --> 01:08:59,634
hidden? Things like that,       
but you can override it,        

1406
01:08:59,702 --> 01:09:02,803
get the super file attributes   
it would normally return.       

1407
01:09:02,872 --> 01:09:06,507
And then add this very special  
dictionary item called          

1408
01:09:06,576 --> 01:09:10,778
URLResourceKey.thumbnailDicti-  
onaryKey. And the value of it   

1409
01:09:10,846 --> 01:09:14,415
actually is another             
dictionary. With the key being  

1410
01:09:14,484 --> 01:09:19,620
ThumbnailDictionaryItem.NSThu-  
mbnail1024x1024SizeKey. And     

1411
01:09:19,689 --> 01:09:24,759
the value is a UIImage. So you  
add this to the dictionary,     

1412
01:09:24,828 --> 01:09:27,929
if you have a UIImage to be     
the thumbnail, and return it.   

1413
01:09:27,997 --> 01:09:31,766
Now, it says there              
NSThumbnail1024x1024, but       

1414
01:09:31,835 --> 01:09:34,402
it actually can be any size.    

1415
01:09:34,471 --> 01:09:37,105
It seems to me that if          
the size gets too small,        

1416
01:09:37,173 --> 01:09:40,040
then it will start using        
the icon for the file. So       

1417
01:09:40,109 --> 01:09:43,411
it can't be too small, and I'm  
not sure what too small is,     

1418
01:09:43,479 --> 01:09:46,513
probably has something to do    
with how big the icon image     

1419
01:09:46,582 --> 01:09:49,050
is. Maybe if it gets smaller    
than the icon image,            

1420
01:09:49,119 --> 01:09:50,718
I'm really not sure             
how it chooses.                 

1421
01:09:50,787 --> 01:09:53,654
But, as long as the image       
is decent sized,                

1422
01:09:53,723 --> 01:09:56,323
and I don't know if             
there's a limit too             

1423
01:09:56,392 --> 01:09:59,060
big. But you probably wouldn't  
want to waste your time         

1424
01:09:59,129 --> 01:10:01,228
creating anything               
bigger than 1024x1024,          

1425
01:10:01,297 --> 01:10:04,832
cuz it's gonna be a thumbnail.  
It's gonna be small showing in  

1426
01:10:04,901 --> 01:10:08,802
the files app or whatever,      
you can return it, so           

1427
01:10:08,871 --> 01:10:13,174
we'll do this in the demo       
on Wednesday as well.           

1428
01:10:13,242 --> 01:10:15,442
So there's some other           
things in UIDocument,           

1429
01:10:15,511 --> 01:10:17,845
like localizedName.             
It will look at the URL, and    

1430
01:10:17,913 --> 01:10:20,748
get the name at the end of      
the URL, and things like that.  

1431
01:10:20,817 --> 01:10:23,684
You can find out if you have    
any unsaved changes currently,  

1432
01:10:23,753 --> 01:10:25,953
you can get the date that       
a file was last saved,          

1433
01:10:26,021 --> 01:10:28,555
you can even do userActivity.   
Which is this thing where       

1434
01:10:28,624 --> 01:10:30,624
you start working on            
something on one device and     

1435
01:10:30,693 --> 01:10:32,092
then you go continue            
on another.                     

1436
01:10:32,161 --> 01:10:36,396
And you'll be exactly where     
you were before. So we're out   

1437
01:10:36,465 --> 01:10:39,166
of time today, I did have one   
more topic, which we'll start   

1438
01:10:39,235 --> 01:10:42,437
off Wednesday. Which is the     
UIDocumentBrowserViewControl-   

1439
01:10:42,505 --> 01:10:46,507
ler. Which is an awesome way    
to give a very powerful user    

1440
01:10:46,576 --> 01:10:51,446
interface for your user inside  
your own app. To create files,  

1441
01:10:51,514 --> 01:10:55,149
move files, delete files,       
put them in folders, you know,  

1442
01:10:55,218 --> 01:10:58,118
drag them from iCloud drive     
to your local hard disk.        

1443
01:10:58,187 --> 01:11:01,455
All this stuff, you get this    
powerful UI, very little work   

1444
01:11:01,524 --> 01:11:04,659
on your part as long as you     
have the UIDocument based app.  

1445
01:11:04,727 --> 01:11:06,828
So, we'll start off Wednesday,  
I'll tell you about that.       

1446
01:11:06,896 --> 01:11:09,997
And then I'll dive into         
converting emoji art to be      

1447
01:11:10,065 --> 01:11:13,434
a UIDocument based app that     
uses all of this cool UI and    

1448
01:11:13,503 --> 01:11:16,504
all that stuff. Friday, no      
more sections, so there's no    

1449
01:11:16,572 --> 01:11:19,207
Friday section. Next week,      
I'll be talking about, alerts,  

1450
01:11:19,275 --> 01:11:21,809
notifications, I mentioned      
that, applications lifecycle,   

1451
01:11:21,878 --> 01:11:24,912
that app delegate thing.        
And some more about segues,     

1452
01:11:24,981 --> 01:11:27,748
more segues that we haven't     
talked about as yet.            

1453
01:11:27,817 --> 01:11:31,986
So that's all what we're        
doing next time, all right?     

1454
01:11:32,054 --> 01:11:35,656
I will see you then.            
>> For more, please visit us,   

1455
01:11:35,724 --> 01:11:37,458
at stanford.edu.                
