Fix ScrollTo on Mac (#4983) * fixes #3319

* Fix github issue #3319

Fix  #3319 [MAC] ScrollTo method is not working in Xamarin.Forms for mac platform

* Update Issue3318.cs

Fix Issue3318 UITest.

* Fix github issue #3319

Fix  #3319 [MAC] ScrollTo method is not working in Xamarin.Forms for mac platform

* Update Issue3318.cs

Fix Issue3318 UITest.

Author: sanyandreichuk

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue3318.cs

@@ -0,0 +1,85 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Text;
+using System.Threading.Tasks;
+using System.Linq;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+using Xamarin.Forms.Core.UITests;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 3318, "[MAC] ScrollTo method is not working in Xamarin.Forms for mac platform", PlatformAffected.macOS)]
+
+	public class Issue3318 : TestContentPage
+	{
+		protected override void Init()
+		{
+			var stackLayout = new StackLayout();
+
+			var list = Enumerable.Range(0, 40).Select(c => $"Item {c}").ToArray();
+			var listview = new ListView { ItemsSource = list };
+
+			var swShouldAnimate = new Switch();
+			var lblShouldAnimate = new Label { Text = "Should Animate?" };
+
+			var btnMakeVisible = new Button { Text = "Make Visible" };
+			btnMakeVisible.Clicked += (s, e) =>
+			{
+				listview.ScrollTo(list[19], ScrollToPosition.MakeVisible, swShouldAnimate.IsToggled);
+			};
+
+			var btnCenter = new Button { Text = "Center" };
+			btnCenter.Clicked += (s, e) =>
+			{
+				listview.ScrollTo(list[19], ScrollToPosition.Center, swShouldAnimate.IsToggled);
+			};
+
+			var btnStart = new Button { Text = "Start" };
+			btnStart.Clicked += (s, e) =>
+			{
+				listview.ScrollTo(list[19], ScrollToPosition.Start, swShouldAnimate.IsToggled);
+			};
+
+			var btnEnd = new Button { Text = "End" };
+			btnEnd.Clicked += (s, e) =>
+			{
+				listview.ScrollTo(list[19], ScrollToPosition.End, swShouldAnimate.IsToggled);
+			};
+
+			stackLayout.Children.Add(btnMakeVisible);
+			stackLayout.Children.Add(btnCenter);
+			stackLayout.Children.Add(btnStart);
+			stackLayout.Children.Add(btnEnd);
+
+			var shouldAnimateContainer = new StackLayout { Orientation = StackOrientation.Horizontal };
+			shouldAnimateContainer.Children.Add(swShouldAnimate);
+			shouldAnimateContainer.Children.Add(lblShouldAnimate);
+
+			stackLayout.Children.Add(shouldAnimateContainer);
+			stackLayout.Children.Add(listview);
+
+			Content = stackLayout;
+		}
+
+
+#if UITEST
+		[Test]
+		public void Issue3318Test()
+		{
+			RunningApp.WaitForElement (q => q.Marked ("End"));
+			RunningApp.Tap (q => q.Marked ("End"));
+			RunningApp.WaitForElement (q => q.Marked ("Item 19"));
+			RunningApp.Back ();
+		}
+#endif
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -877,6 +877,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue3622.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue4138.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue4314.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue3318.cs" />
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Bugzilla22229.xaml">

Xamarin.Forms.Platform.MacOS/Renderers/ListViewRenderer.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Linq;
@@ -346,9 +347,66 @@ void UpdateSeparatorVisibility()
 		{
 		}
 
-		//TODO: Implement ScrollTo
 		void OnScrollToRequested(object sender, ScrollToRequestedEventArgs e)
 		{
+			var templatedItems = TemplatedItemsView.TemplatedItems;
+			var scrollArgs = (ITemplatedItemsListScrollToRequestedEventArgs)e;
+
+			var row = templatedItems?.GetGlobalIndexOfItem(scrollArgs.Item) ?? -1;
+			if (row == -1)
+				return;
+
+			var rowRect = _table.RectForRow(row);
+			var rowHeight = rowRect.Height;
+			var clipView = _table.Superview as NSClipView;
+			var clipViewHeight = clipView.Frame.Height;
+			var scrollToPosition = e.Position;
+
+			if (scrollToPosition == ScrollToPosition.MakeVisible)
+			{
+				var topVisibleY = clipView.Bounds.Y;
+				var bottomVisibleY = clipView.Bounds.Y + clipViewHeight - rowHeight;
+
+				if (topVisibleY > rowRect.Y)
+				{
+					scrollToPosition = ScrollToPosition.Start;
+				}
+				else if (bottomVisibleY < rowRect.Y)
+				{
+					scrollToPosition = ScrollToPosition.End;
+				}
+				else
+				{
+					return;
+				}
+			}
+
+			nfloat y = 0;
+			var scrollOrigin = rowRect.Location;
+
+			if (scrollToPosition == ScrollToPosition.Center)
+			{
+				y = (scrollOrigin.Y - clipViewHeight / 2) + rowHeight / 2;
+			}
+			else if (scrollToPosition == ScrollToPosition.End)
+			{
+				y = scrollOrigin.Y - clipViewHeight + rowHeight;
+			}
+			else
+			{
+				y = scrollOrigin.Y;
+			}
+
+			scrollOrigin.Y = y;
+
+			if (e.ShouldAnimate)
+			{
+				((NSView)clipView.Animator).SetBoundsOrigin(scrollOrigin);
+			}
+			else
+			{
+				clipView.SetBoundsOrigin(scrollOrigin);
+			}
 		}
 
 		//TODO: Implement Footer