[macOS] Align FLEPlugin with iOS Flutter

Changes FLEPlugin to be a subset of iOS's FlutterPlugin's API, including
changing the plugin creation and registration system. Plugins now create
and manage their own channels, instead of relying on FLEViewController
for high-level message APIs.

This is a breaking change for any FLEPlugin implementation, as well as
application-level code that was calling addPlugin:. (The later may
require additional changes in the future as noted in the comment on
registerPlugin:, but the plugin implemention API should now be stable.)

This essentially completes issue google#102 for macOS.

Author: stuartmorgan-g

example/macos/ExampleWindow.swift

@@ -18,9 +18,9 @@ class ExampleWindow: NSWindow {
   @IBOutlet weak var flutterViewController: FLEViewController!
 
   override func awakeFromNib() {
-    flutterViewController.add(FLEColorPanelPlugin())
-    flutterViewController.add(FLEFileChooserPlugin())
-    flutterViewController.add(FLEMenubarPlugin())
+    flutterViewController.register(FLEColorPanelPlugin.self)
+    flutterViewController.register(FLEFileChooserPlugin.self)
+    flutterViewController.register(FLEMenubarPlugin.self)
 
     let assets = NSURL.fileURL(withPath: "flutter_assets", relativeTo: Bundle.main.resourceURL)
     // Pass through argument zero, since the Flutter engine expects to be processing a full

library/macos/FLEKeyEventPlugin.h

@@ -18,52 +18,38 @@
 #import "FLEMethodChannel.h"
 #import "FLEMethodCodec.h"
 
-@class FLEViewController;
+@protocol FLEPluginRegistrar;
 
 /**
- * A plugin is an object that can respond appropriately to Flutter platform messages over a specific
- * named system channel. See https://flutter.io/platform-channels/.
+ * Implemented by the platform side of a Flutter plugin.
  *
- * Note: This interface will be changing in the future to more closely match the iOS Flutter
- * platform message API. It will be a one-time breaking change.
+ * Defines a set of optional callback methods and a method to set up the plugin
+ * and register it to be called by other application components.
+ *
+ * Currently FLEPlugin has very limited functionality, but is expected to expand over time to
+ * more closely match the functionality of FlutterPlugin.
  */
 @protocol FLEPlugin <NSObject>
 
 /**
- * A weak reference to the owning controller. May be used to send messages to the Flutter
- * framework.
+ * Creates an instance of the plugin to register with |registrar| using the desired
+ * FLEPluginRegistrar methods.
  */
-@property(nullable, weak) FLEViewController *controller;
++ (void)registerWithRegistrar:(nonnull id<FLEPluginRegistrar>)registrar;
 
-/**
- * The name of the system channel via which this plugin communicates.
- */
-@property(nonnull, readonly) NSString *channel;
+@optional
 
 /**
- * Called when a message is sent from Flutter on this plugin's channel.
- * The result callback must be called exactly once, with one of:
+ * Called when a message is sent from Flutter on a channel that a plugin instance has subscribed
+ * to via -[FLEPluginRegistrar addMethodCallDelegate:channel:].
+ *
+ * The |result| callback must be called exactly once, with one of:
  * - FLEMethodNotImplemented, if the method call is unknown.
  * - An FLEMethodError, if the method call was understood but there was a
  *   problem handling it.
  * - Any other value (including nil) to indicate success. The value will
  *   be returned to the Flutter caller, and must be serializable to JSON.
- *
- * If handling the method involves multiple responses to Flutter, follow-up
- * messages can be sent by calling the other direction using
- * -[FLEViewController invokeMethod:arguments:onChannel:].
  */
 - (void)handleMethodCall:(nonnull FLEMethodCall *)call result:(nonnull FLEMethodResult)result;
 
-@optional
-
-/**
- * If implemented, returns the codec to use for method calls to this plugin.
- *
- * If not implemented, the codec is assumed to be FLEJSONMethodCodec. Note that this is different
- * from existing Flutter platforms, which default to the standard codec; this is to preserve
- * backwards compatibility for FLEPlugin until the breaking change for the platform messages API.
- */
-@property(nonnull, readonly) id<FLEMethodCodec> codec;
-
 @end

library/macos/FLEKeyEventPlugin.m

@@ -0,0 +1,48 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#import <Cocoa/Cocoa.h>
+
+#import "FLEBinaryMessenger.h"
+#import "FLEMethodChannel.h"
+
+/**
+ * The protocol for an object managing registration for a plugin. It provides access to application
+ * context, as as allowing registering for callbacks for handling various conditions.
+ *
+ * Currently FLEPluginRegistrar has very limited functionality, but is expected to expand over time
+ * to more closely match the functionality of FlutterPluginRegistrar.
+ */
+@protocol FLEPluginRegistrar <NSObject>
+
+/**
+ * The binary messenger used for creating channels to communicate with the Flutter engine.
+ */
+@property(nonnull, readonly) id<FLEBinaryMessenger> messenger;
+
+/**
+ * The view displaying Flutter content.
+ *
+ * WARNING: If/when multiple Flutter views within the same application are supported (#98), this
+ * API will change.
+ */
+@property(nullable, readonly) NSView *view;
+
+/**
+ * Registers |delegate| to receive handleMethodCall:result: callbacks for the given |channel|.
+ */
+- (void)addMethodCallDelegate:(nonnull id<FLEPlugin>)delegate
+                      channel:(nonnull FLEMethodChannel *)channel;
+
+@end

library/macos/FLEPlugin.h

@@ -14,13 +14,23 @@
 
 #import <Cocoa/Cocoa.h>
 
-#import "FLEPlugin.h"
+#import "FLEBinaryMessenger.h"
+#import "FLEViewController.h"
 
 /**
- * A FlutterPlugin to handle text input. Owned by the FlutterViewController.
- * Responsible for bridging the native macOS text input system with the
- * Flutter framework text editing classes, via system channels.
+ * A plugin to handle text input.
+ *
+ * Responsible for bridging the native macOS text input system with the Flutter framework text
+ * editing classes, via system channels.
+ *
+ * This is not an FLEPlugin since it needs access to FLEViewController internals, so needs to be
+ * managed differently.
  */
-@interface FLETextInputPlugin : NSResponder <FLEPlugin>
+@interface FLETextInputPlugin : NSResponder
+
+/**
+ * Initializes a text input plugin that coordinates key event handling with |viewController|.
+ */
+- (instancetype)initWithViewController:(FLEViewController*)viewController;
 
 @end

library/macos/FLEPluginRegistrar.h

@@ -16,6 +16,7 @@
 
 #import <objc/message.h>
 
+#import "FLEJSONMethodCodec.h"
 #import "FLETextInputModel.h"
 #import "FLEViewController+Internal.h"
 
@@ -33,7 +34,6 @@
 static NSString *const kNewLine = @"TextInputAction.newline";
 static NSString *const kDone = @"TextInputAction.done";
 
-
 /**
  * Private properties of FlutterTextInputPlugin.
  */
@@ -42,42 +42,61 @@ @interface FLETextInputPlugin () <NSTextInputClient>
 /**
  * A text input context, representing a connection to the Cocoa text input system.
  */
-@property NSTextInputContext *textInputContext;
+@property(nonatomic) NSTextInputContext *textInputContext;
 
 /**
  * A dictionary of text input models, one per client connection, keyed
  * by the client connection ID.
  */
-@property NSMutableDictionary<NSNumber *, FLETextInputModel *> *textInputModels;
+@property(nonatomic) NSMutableDictionary<NSNumber *, FLETextInputModel *> *textInputModels;
 
 /**
  * The currently active client connection ID.
  */
-@property(nullable) NSNumber *activeClientID;
+@property(nonatomic, nullable) NSNumber *activeClientID;
 
 /**
  * The currently active text input model.
  */
-@property(readonly, nullable) FLETextInputModel *activeModel;
+@property(nonatomic, readonly, nullable) FLETextInputModel *activeModel;
+
+/**
+ * The channel used to communicate with Flutter.
+ */
+@property(nonatomic) FLEMethodChannel *channel;
+
+/**
+ * The FLEViewController to manage input for.
+ */
+@property(nonatomic, weak) FLEViewController *flutterViewController;
+
+/**
+ * Handles a Flutter system message on the text input channel.
+ */
+- (void)handleMethodCall:(FLEMethodCall *)call result:(FLEMethodResult)result;
 
 @end
 
 @implementation FLETextInputPlugin
 
-@synthesize controller = _controller;
-
-- (instancetype)init {
+- (instancetype)initWithViewController:(FLEViewController *)viewController {
   self = [super init];
   if (self != nil) {
+    _flutterViewController = viewController;
+    _channel = [FLEMethodChannel methodChannelWithName:kTextInputChannel
+                                       binaryMessenger:viewController
+                                                 codec:[FLEJSONMethodCodec sharedInstance]];
+    __weak FLETextInputPlugin *weakSelf = self;
+    [_channel setMethodCallHandler:^(FLEMethodCall *call, FLEMethodResult result) {
+      [weakSelf handleMethodCall:call result:result];
+    }];
     _textInputModels = [[NSMutableDictionary alloc] init];
     _textInputContext = [[NSTextInputContext alloc] initWithClient:self];
   }
   return self;
 }
 
-- (NSString *)channel {
-  return kTextInputChannel;
-}
+#pragma mark - Private
 
 - (FLETextInputModel *)activeModel {
   return (_activeClientID == nil) ? nil : _textInputModels[_activeClientID];
@@ -95,10 +114,10 @@ - (void)handleMethodCall:(FLEMethodCall *)call result:(FLEMethodResult)result {
       _textInputModels[_activeClientID] = [[FLETextInputModel alloc] init];
     }
   } else if ([method isEqualToString:kShowMethod]) {
-    [self.controller addKeyResponder:self];
+    [self.flutterViewController addKeyResponder:self];
     [_textInputContext activate];
   } else if ([method isEqualToString:kHideMethod]) {
-    [self.controller removeKeyResponder:self];
+    [self.flutterViewController removeKeyResponder:self];
     [_textInputContext deactivate];
   } else if ([method isEqualToString:kClearClientMethod]) {
     _activeClientID = nil;
@@ -120,9 +139,8 @@ - (void)updateEditState {
     return;
   }
 
-  [_controller invokeMethod:kUpdateEditStateResponseMethod
-                  arguments:@[ _activeClientID, _textInputModels[_activeClientID].state ]
-                  onChannel:kTextInputChannel];
+  [_channel invokeMethod:kUpdateEditStateResponseMethod
+               arguments:@[ _activeClientID, _textInputModels[_activeClientID].state ]];
 }
 
 #pragma mark -
@@ -226,9 +244,7 @@ - (void)insertNewline:(id)sender {
   // There is a PR in Flutter to identify if the widget is multiline, and act accordingly
   // (https://github.com/flutter/flutter/pull/23015). Once merged, this action should be changed
   // to kNewLine.
-  [_controller invokeMethod:kPerformAction
-                  arguments:@[ _activeClientID, kDone ]
-                  onChannel:kTextInputChannel];
+  [_channel invokeMethod:kPerformAction arguments:@[ _activeClientID, kDone ]];
 }
 
 - (void)setMarkedText:(id)string

library/macos/FLETextInputPlugin.h

@@ -27,10 +27,4 @@
  */
 - (void)removeKeyResponder:(nonnull NSResponder *)responder;
 
-/**
- * Sends a platform message to the Flutter engine on the given channel.
- * @param message The raw message.
- */
-- (void)dispatchMessage:(nonnull NSDictionary *)message onChannel:(nonnull NSString *)channel;
-
 @end