[iOS] Clear the delegate from ContextActionCell (#4324) fixes #4314

* [Controls] Add repo for issue #4341

* [iOS] Clear the global closer delegate from ContextActionCell when disposing

* [Controls] Rename to correct issue number

* [Controls] Try fix opening context menu on iOS10

* [Controls] Add more testing to #4314

* [iOS] Fix Globalcloser when no cell exists

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue4314.cs

@@ -0,0 +1,57 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.ContextActions)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 4314, "When ListView items is removed and it is empty, Xamarin Forms crash", PlatformAffected.iOS)]
+	public class Issue4314 : TestNavigationPage // or TestMasterDetailPage, etc ...
+	{
+		const string Success = "Success";
+#if !UITEST
+		MessagesViewModel viewModel;
+		protected override void Init()
+		{
+			var page = new ContextActionsGallery(false, true, 2) { Title = "Swipe and delete both" };
+			viewModel = page.BindingContext as MessagesViewModel;
+			viewModel.Messages.CollectionChanged += (s, e) =>
+			{
+				if (viewModel.Messages.Count == 0)
+				{
+					Navigation.PushAsync(new ContentPage { Title = "Success", Content = new Label { Text = Success } });
+				}
+			};
+			Navigation.PushAsync(page);
+		}
+#else
+		protected override void Init()
+		{
+		}
+#endif
+#if UITEST && __IOS__
+		[Test]
+		public void Issue4341Test() 
+		{
+			RunningApp.WaitForElement(c=> c.Marked("Email"));
+			RunningApp.ActivateContextMenu("Subject Line 0");
+			RunningApp.WaitForElement("Delete");
+			RunningApp.Tap("Delete");
+			RunningApp.ActivateContextMenu("Subject Line 1");
+			RunningApp.Tap("Delete");
+			RunningApp.WaitForElement(c=> c.Marked(Success));
+			RunningApp.Back();
+			RunningApp.WaitForElement(c => c.Marked("Email"));
+			RunningApp.SwipeRightToLeft();
+		}
+#endif
+	}
+}

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

@@ -820,6 +820,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue3884.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue4001.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue4138.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue4314.cs" />
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Bugzilla22229.xaml">

Xamarin.Forms.Controls/GalleryPages/EditableList.cs

@@ -7,9 +7,9 @@ namespace Xamarin.Forms.Controls
 {
 	internal class MessagesViewModel : ViewModelBase
 	{
-		public MessagesViewModel()
+		public MessagesViewModel(int messagesCount)
 		{
-			Messages = new ObservableCollection<MessageViewModel> (Enumerable.Range (0, 100).Select (i => {
+			Messages = new ObservableCollection<MessageViewModel> (Enumerable.Range (0, messagesCount).Select (i => {
 				return new MessageViewModel { Subject = "Subject Line " + i, MessagePreview = "Lorem ipsum dolorem monkeys bonkers " + i };
 			}));
 
@@ -26,7 +26,7 @@ namespace Xamarin.Forms.Controls
 	}
 
 	[Preserve (AllMembers = true)]
-	internal class MessageViewModel : ViewModelBase
+	public class MessageViewModel : ViewModelBase
 	{
 		public MessageViewModel()
 		{
@@ -86,13 +86,16 @@ namespace Xamarin.Forms.Controls
 			}
 		}
 
-		public ContextActionsGallery (bool tableView = false)
+		public ContextActionsGallery (bool tableView = false, bool hasUnevenRows = false, int messagesCount = 100)
 		{
-			BindingContext = new MessagesViewModel();
+			BindingContext = new MessagesViewModel(messagesCount);
 
 			View list;
 			if (!tableView) {
-				list = new ListView();
+				list = new ListView
+				{
+					HasUnevenRows = hasUnevenRows
+				};
 				list.SetBinding (ListView.ItemsSourceProperty, "Messages");
 				((ListView)list).ItemTemplate = new DataTemplate (typeof (MessageCell));
 			} else {

Xamarin.Forms.Platform.iOS/ContextActionCell.cs

@@ -276,6 +276,7 @@ namespace Xamarin.Forms.Platform.iOS
 
 				if (_scroller != null)
 				{
+					_scroller.Delegate = null;
 					_scroller.Dispose();
 					_scroller = null;
 				}

Xamarin.Forms.Platform.iOS/ContextScrollViewDelegate.cs

@@ -125,7 +125,7 @@ namespace Xamarin.Forms.Platform.iOS
 				RestoreHighlight(scrollView);
 
 				s_scrollViewBeingScrolled = null;
-				ClearCloserRecognizer(scrollView);
+				ClearCloserRecognizer(GetContextCell(scrollView));
 				ClosedCallback?.Invoke();
 			}
 		}
@@ -133,7 +133,7 @@ namespace Xamarin.Forms.Platform.iOS
 		public void Unhook(UIScrollView scrollView)
 		{
 			RestoreHighlight(scrollView);
-			ClearCloserRecognizer(scrollView);
+			ClearCloserRecognizer(GetContextCell(scrollView));
 		}
 
 		public override void WillEndDragging(UIScrollView scrollView, PointF velocity, ref PointF targetContentOffset)
@@ -158,36 +158,35 @@ namespace Xamarin.Forms.Platform.iOS
 					while (view.Superview != null)
 					{
 						view = view.Superview;
-
-						NSAction close = () =>
-						{
-							if (UIDevice.CurrentDevice.CheckSystemVersion(8, 0))
-								RestoreHighlight(scrollView);
-
-							IsOpen = false;
-							scrollView.SetContentOffset(new PointF(0, 0), true);
-
-							ClearCloserRecognizer(scrollView);
-						};
-
 						var table = view as UITableView;
 						if (table != null)
 						{
+							ContextActionsCell contentCell = GetContextCell(scrollView);
+							NSAction close = () =>
+							{
+								if (UIDevice.CurrentDevice.CheckSystemVersion(8, 0))
+									RestoreHighlight(scrollView);
+
+								IsOpen = false;
+								scrollView.SetContentOffset(new PointF(0, 0), true);
+								ClearCloserRecognizer(contentCell);
+								contentCell = null;
+							};
+
 							_table = table;
 							_globalCloser = new GlobalCloseContextGestureRecognizer(scrollView, close);
 							_globalCloser.ShouldRecognizeSimultaneously = (recognizer, r) => r == _table.PanGestureRecognizer;
 							table.AddGestureRecognizer(_globalCloser);
 
 							_closer = new UITapGestureRecognizer(close);
-							var cell = GetContextCell(scrollView);
-							cell.ContentCell.AddGestureRecognizer(_closer);
+							contentCell.AddGestureRecognizer(_closer);
 						}
 					}
 				}
 			}
 			else
 			{
-				ClearCloserRecognizer(scrollView);
+				ClearCloserRecognizer(GetContextCell(scrollView));
 
 				IsOpen = false;
 				targetContentOffset = new PointF(0, 0);
@@ -234,13 +233,12 @@ namespace Xamarin.Forms.Platform.iOS
 			base.Dispose(disposing);
 		}
 
-		void ClearCloserRecognizer(UIScrollView scrollView)
+		void ClearCloserRecognizer(ContextActionsCell cell)
 		{
 			if (_globalCloser == null || _globalCloser.State == UIGestureRecognizerState.Cancelled)
 				return;
 
-			var cell = GetContextCell(scrollView);
-			cell.ContentCell.RemoveGestureRecognizer(_closer);
+			cell?.ContentCell?.RemoveGestureRecognizer(_closer);
 			_closer.Dispose();
 			_closer = null;
 
@@ -252,9 +250,9 @@ namespace Xamarin.Forms.Platform.iOS
 
 		ContextActionsCell GetContextCell(UIScrollView scrollView)
 		{
-			var view = scrollView.Superview.Superview;
+			var view = scrollView?.Superview?.Superview;
 			var cell = view as ContextActionsCell;
-			while (view.Superview != null)
+			while (view?.Superview != null)
 			{
 				cell = view as ContextActionsCell;
 				if (cell != null)