[iOS] Clear prototype cell on UnevenRows (#1569)

* [Controls]Add repo for github 1567

* [iOS] Make sure to clear the prototype cell because renderers were disposed.

* [Controls] Add IssueTestNumber

* [UITest] Add Preserve to fix android test

* [iOS] Better fix for invalidate prototype cell

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/GitHub1567.cs

@@ -0,0 +1,106 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using System.Windows.Input;
+using System.Collections.ObjectModel;
+using System.Threading;
+using System.Threading.Tasks;
+using System;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 1567, "NRE using TapGestureRecognizer on cell with HasUnevenRows", PlatformAffected.iOS, issueTestNumber: 1)]
+	public class GitHub1567 : TestContentPage // or TestMasterDetailPage, etc ...
+	{
+		ICommand SomeCommand;
+		ObservableCollection<LocalIem> LocalList { get; set; } = new ObservableCollection<LocalIem>();
+
+		protected override async void Init()
+		{
+			// Initialize ui here instead of ctor
+			var btn = new Button
+			{
+				AutomationId = "btnFillData",
+				Text = "FILL DATA",
+				Command = new Command(async () => { await FillData(); })
+			};
+			var lst = new ListView(ListViewCachingStrategy.RecycleElement)
+			{
+				Header = btn,
+				HasUnevenRows = true,
+				RowHeight = -1,
+				SeparatorVisibility = SeparatorVisibility.None,
+				ItemsSource = LocalList,
+				ItemTemplate = new DataTemplate(typeof(CustomCell))
+			};
+
+			Content = lst;
+			this.BindingContext = this;
+			SomeCommand = new Command(SomeCommandAction);
+			await FillData();
+		}
+
+        [Preserve(AllMembers = true)]
+		class CustomCell : ViewCell
+		{
+			public CustomCell()
+			{
+				var lbl = new Label { FontSize = 14 };
+				lbl.SetBinding(Label.TextProperty, "Value1");
+				var grd = new Grid();
+				var boxView = new BoxView
+				{
+					BackgroundColor = Color.Transparent,
+					HorizontalOptions = LayoutOptions.FillAndExpand,
+					VerticalOptions = LayoutOptions.FillAndExpand
+				};
+				var gesture = new TapGestureRecognizer();
+				gesture.SetBinding(TapGestureRecognizer.CommandProperty, "SomeCommand");
+				boxView.GestureRecognizers.Add(gesture);
+				grd.Children.Add(lbl);
+				grd.Children.Add(boxView);
+				View = grd;
+			}
+		}
+
+		void SomeCommandAction(object obj)
+		{		
+		}
+		
+		async Task FillData()
+		{
+			await Task.Factory.StartNew(async () =>
+			{
+				await Task.Delay(100);
+				LocalList.Clear();
+				for (int i = 0; i < 100; i++)
+				{
+					LocalList.Add(new LocalIem()
+					{
+						Value1 = DateTime.UtcNow.Ticks.ToString(),
+					});
+				}
+			}, CancellationToken.None, TaskCreationOptions.LongRunning, TaskScheduler.Default);
+		}
+
+        [Preserve(AllMembers = true)]
+		class LocalIem
+		{
+			public string Value1 { get; set; }
+		}
+
+#if UITEST
+		[Test]
+		public void GitHub1567Test()
+		{
+			RunningApp.WaitForElement(q => q.Marked("btnFillData"));
+			RunningApp.Tap(q => q.Marked("btnFillData"));
+		}
+#endif
+	}
+}

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

@@ -341,6 +341,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla60524.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla59925.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue1436.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)GitHub1567.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue1909.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)_Template.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla42620.cs" />

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

@@ -552,7 +552,8 @@ namespace Xamarin.Forms.Platform.iOS
 					Control.EndUpdates();
 
 					if (_estimatedRowHeight && TemplatedItemsView.TemplatedItems.Count == 0)
-						_estimatedRowHeight = false;
+						InvalidateCellCache();
+
 
 					break;
 
@@ -576,7 +577,7 @@ namespace Xamarin.Forms.Platform.iOS
 					Control.EndUpdates();
 
 					if (_estimatedRowHeight && e.OldStartingIndex == 0)
-						_estimatedRowHeight = false;
+						InvalidateCellCache();
 
 					break;
 
@@ -588,17 +589,24 @@ namespace Xamarin.Forms.Platform.iOS
 					Control.EndUpdates();
 
 					if (_estimatedRowHeight && e.OldStartingIndex == 0)
-						_estimatedRowHeight = false;
+						InvalidateCellCache();
+
 
 					break;
 
 				case NotifyCollectionChangedAction.Reset:
-					_estimatedRowHeight = false;
+					InvalidateCellCache();
 					Control.ReloadData();
 					return;
 			}
 		}
 
+		void InvalidateCellCache()
+		{
+			_estimatedRowHeight = false;
+			_dataSource.InvalidatePrototypicalCellCache();
+		}
+
 		void UpdatePullToRefreshEnabled()
 		{
 			if (_tableViewController != null)
@@ -703,6 +711,7 @@ namespace Xamarin.Forms.Platform.iOS
 
 			internal override void InvalidatePrototypicalCellCache()
 			{
+				ClearPrototype();
 				_prototypicalCellByTypeOrDataTemplate.Clear();
 			}
 
@@ -792,15 +801,22 @@ namespace Xamarin.Forms.Platform.iOS
 
 				if (disposing)
 				{
-					if (_prototype != null)
-					{
-						_prototype.Dispose();
-						_prototype = null;
-					}
+					ClearPrototype();
 				}
 
 				base.Dispose(disposing);
 			}
+
+			void ClearPrototype()
+			{
+				if (_prototype != null)
+				{
+					var element = _prototype.Element;
+					element?.ClearValue(Platform.RendererProperty);
+					_prototype?.Dispose();
+					_prototype = null;
+				}
+			}
 		}
 
 		internal class ListViewDataSource : UITableViewSource