[All] Crash fixes for ListViews (#243)beta-2.3.1-pre2

* [Controls] Add repro for 42277

* [Android] No crash if GroupHeaderTemplate=null

* [Android] Fix DataTemplateSelector crash

* [Core] Expose ListProxy on TIL

* [iOS] Fix DataTemplateSelector crash

* [Win] Fix DataTemplateSelector crash

* [Docs] Update docs

* [Core] Implement ListProxy explicitly

Allows ListProxy property to stay internal.

* [Controls] Revert unnecessary change to shproj

8 files changed, 154 insertions, 9 deletions

diff --git a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla42277.cs b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla42277.cs
new file mode 100644
index 00000000..1a7624ae
--- /dev/null
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla42277.cs
@@ -0,0 +1,121 @@
+using System;
+using System.Linq;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using System.Collections.Generic;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Bugzilla, 42277, "DataTemplate System.InvalidCastException crash in 2.3.1-pre1")]
+	public class Bugzilla42277 : TestContentPage
+	{
+		const string Success1 = "Success1";
+		const string Success2 = "Success2";
+		const string Success3 = "GroupedSuccess3";
+		const string Success4 = "GroupedSuccess4";
+		const string Success5 = "GroupedSuccess5";
+		const string Success6 = "GroupedSuccess6";
+
+		class MyDataTemplateSelector : DataTemplateSelector
+		{
+			DataTemplate _1Template;
+			DataTemplate _2Template;
+
+			DataTemplate _3Template;
+			DataTemplate _4Template;
+			DataTemplate _5Template;
+			DataTemplate _6Template;
+
+			public MyDataTemplateSelector()
+			{
+				_1Template = new DataTemplate(() =>
+				{
+					return new TextCell { Text = Success1 };
+				});
+
+				_2Template = new DataTemplate(() =>
+				{
+					return new TextCell { Text = Success2 };
+				});
+
+				_3Template = new DataTemplate(() =>
+				{
+					return new TextCell { Text = Success3 };
+				});
+
+				_4Template = new DataTemplate(() =>
+				{
+					return new TextCell { Text = Success4 };
+				});
+
+				_5Template = new DataTemplate(() =>
+				{
+					return new TextCell { Text = Success5 };
+				});
+
+				_6Template = new DataTemplate(() =>
+				{
+					return new TextCell { Text = Success6 };
+				});
+			}
+
+			protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
+			{
+				int number = (int)item;
+				switch (number)
+				{
+					default:
+					case 0: return _1Template;
+					case 1: return _2Template;
+					case 2: return _3Template;
+					case 3: return _4Template;
+					case 4: return _5Template;
+					case 5: return _6Template;
+				}
+			}
+		}
+
+		protected override void Init()
+		{
+			//test non-grouped DTS
+			ListView listView = new ListView(ListViewCachingStrategy.RecycleElement)
+			{
+				ItemsSource = Enumerable.Range(0, 2),
+				ItemTemplate = new MyDataTemplateSelector()
+			};
+
+			//test grouped DTS
+			ListView groupedListView = new ListView(ListViewCachingStrategy.RecycleElement)
+			{
+				ItemsSource = new List<List<int>> { Enumerable.Range(2, 2).ToList(), Enumerable.Range(4, 2).ToList() },
+				IsGroupingEnabled = true,
+				ItemTemplate = new MyDataTemplateSelector()
+			};
+
+			Content = new StackLayout { Children = { listView, groupedListView } };
+
+			//test collection changed
+			listView.ItemsSource = Enumerable.Range(0, 2);
+			groupedListView.ItemsSource = new List<List<int>> { Enumerable.Range(2, 2).ToList(), Enumerable.Range(4, 2).ToList() };
+		}
+
+#if UITEST
+		[Test]
+		public void Bugzilla42277Test()
+		{
+			RunningApp.WaitForElement(q => q.Marked(Success1));
+			RunningApp.WaitForElement(q => q.Marked(Success2));
+			RunningApp.WaitForElement(q => q.Marked(Success3));
+			RunningApp.WaitForElement(q => q.Marked(Success4));
+			RunningApp.WaitForElement(q => q.Marked(Success5));
+			RunningApp.WaitForElement(q => q.Marked(Success6));
+		}
+#endif
+	}
+}
diff --git a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
index 919d5062..10e0800c 100644
--- a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
@@ -156,6 +156,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla39853.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)TestPages\ScreenshotConditionalApp.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla41842.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Bugzilla42277.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)_Template.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue1028.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue1075.cs" />
diff --git a/Xamarin.Forms.Core/ITemplatedItemsList.cs b/Xamarin.Forms.Core/ITemplatedItemsList.cs
index ae979d71..be9055af 100644
--- a/Xamarin.Forms.Core/ITemplatedItemsList.cs
+++ b/Xamarin.Forms.Core/ITemplatedItemsList.cs
@@ -17,6 +17,8 @@ namespace Xamarin.Forms
 		IEnumerable ItemsSource { get; }
 		IReadOnlyList<string> ShortNames { get; }
 
+		IListProxy ListProxy { get; }
+
 		int GetGlobalIndexForGroup(ITemplatedItemsList<TItem> group);
 		int GetGlobalIndexOfItem(object item);
 		ITemplatedItemsList<TItem> GetGroup(int index);
diff --git a/Xamarin.Forms.Core/TemplatedItemsList.cs b/Xamarin.Forms.Core/TemplatedItemsList.cs
index 75a0d394..cb64e2e9 100644
--- a/Xamarin.Forms.Core/TemplatedItemsList.cs
+++ b/Xamarin.Forms.Core/TemplatedItemsList.cs
@@ -194,6 +194,11 @@ namespace Xamarin.Forms
 			private set { SetValue(ListProxyPropertyKey, value); }
 		}
 
+		IListProxy ITemplatedItemsList<TItem>.ListProxy
+		{
+			get { return ListProxy; }
+		}
+
 		DataTemplate ItemTemplate
 		{
 			get { return (DataTemplate)_itemsView.GetValue(_itemTemplateProperty); }
diff --git a/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs b/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs
index 5ac214cd..2230d2b4 100644
--- a/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs
+++ b/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs
@@ -144,9 +144,9 @@ namespace Xamarin.Forms.Platform.Android
 			{
 				object item = null;
 				if (_listView.IsGroupingEnabled)
-					item = ((ITemplatedItemsView<Cell>)TemplatedItemsView.TemplatedItems.GetGroup(group)).ListProxy[row];
+					item = TemplatedItemsView.TemplatedItems.GetGroup(group).ListProxy[row];
 				else
-					item = ((ITemplatedItemsView<Cell>)TemplatedItemsView.TemplatedItems).ListProxy[position];
+					item = TemplatedItemsView.TemplatedItems.ListProxy[position];
 				itemTemplate = selector.SelectTemplate(item, _listView);
 			}
 			int key;
@@ -405,7 +405,7 @@ namespace Xamarin.Forms.Platform.Android
 				{
 					if (_listView.CachingStrategy == ListViewCachingStrategy.RecycleElement)
 					{
-						var groupContent = _listView.TemplatedItems.GroupHeaderTemplate.CreateContent(group.ItemsSource, _listView) as Cell;
+						var groupContent = _listView.TemplatedItems.GroupHeaderTemplate?.CreateContent(group.ItemsSource, _listView) as Cell;
 						if (groupContent != null)
 						{
 							groupContent.Parent = _listView;
diff --git a/Xamarin.Forms.Platform.WinRT/ListViewRenderer.cs b/Xamarin.Forms.Platform.WinRT/ListViewRenderer.cs
index c6a9d2db..d6ec7038 100644
--- a/Xamarin.Forms.Platform.WinRT/ListViewRenderer.cs
+++ b/Xamarin.Forms.Platform.WinRT/ListViewRenderer.cs
@@ -287,7 +287,7 @@ namespace Xamarin.Forms.Platform.WinRT
 			if (Device.Idiom == TargetIdiom.Phone)
 				await Task.Delay(1);
 
-			IListProxy listProxy = ((ITemplatedItemsView<Cell>)til).ListProxy;
+			IListProxy listProxy = til.ListProxy;
 			ScrollTo(listProxy.ProxiedEnumerable, listProxy[0], ScrollToPosition.Start, true, true);
 		}
 
diff --git a/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs b/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs
index 238759e9..5483a169 100644
--- a/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs
+++ b/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs
@@ -310,7 +310,7 @@ namespace Xamarin.Forms.Platform.iOS
 
 		void OnGroupedCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
 		{
-			var til = (ITemplatedItemsList<Cell>)sender;
+			var til = (TemplatedItemsList<ItemsView<Cell>, Cell>)sender;
 
 			var templatedItems = TemplatedItemsView.TemplatedItems;
 			var groupIndex = templatedItems.IndexOf(til.HeaderContent);
@@ -919,7 +919,7 @@ namespace Xamarin.Forms.Platform.iOS
 			{
 				var templatedItems = TemplatedItemsView.TemplatedItems;
 				if (List.IsGroupingEnabled)
-					templatedItems = (ITemplatedItemsList<Cell>)((IList)templatedItems)[indexPath.Section];
+					templatedItems = (TemplatedItemsList<ItemsView<Cell>, Cell>)((IList)templatedItems)[indexPath.Section];
 
 				var cell = templatedItems[indexPath.Row];
 				return cell;
@@ -934,7 +934,7 @@ namespace Xamarin.Forms.Platform.iOS
 			{
 				var currentSelected = _uiTableView.IndexPathForSelectedRow;
 
-				var til = (ITemplatedItemsView<Cell>)sender;
+				var til = (TemplatedItemsList<ItemsView<Cell>, Cell>)sender;
 				var groupIndex = ((IList)TemplatedItemsView.TemplatedItems).IndexOf(til);
 				if (groupIndex == -1)
 				{
@@ -968,9 +968,9 @@ namespace Xamarin.Forms.Platform.iOS
 
 				var templatedList = TemplatedItemsView.TemplatedItems;
 				if (List.IsGroupingEnabled)
-					templatedList = (ITemplatedItemsList<Cell>)((IList)templatedList)[indexPath.Section];
+					templatedList = (TemplatedItemsList<ItemsView<Cell>, Cell>)((IList)templatedList)[indexPath.Section];
 
-				var item = ((ITemplatedItemsView<Cell>)templatedList).ListProxy[indexPath.Row];
+				var item = templatedList.ListProxy[indexPath.Row];
 
 				itemTemplate = selector.SelectTemplate(item, List);
 				int key;
diff --git a/docs/Xamarin.Forms.Core/Xamarin.Forms/ITemplatedItemsList`1.xml b/docs/Xamarin.Forms.Core/Xamarin.Forms/ITemplatedItemsList`1.xml
index d3e6f449..e526ffab 100644
--- a/docs/Xamarin.Forms.Core/Xamarin.Forms/ITemplatedItemsList`1.xml
+++ b/docs/Xamarin.Forms.Core/Xamarin.Forms/ITemplatedItemsList`1.xml
@@ -239,6 +239,22 @@
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
+    <Member MemberName="ListProxy">
+      <MemberSignature Language="C#" Value="public Xamarin.Forms.IListProxy ListProxy { get; }" />
+      <MemberSignature Language="ILAsm" Value=".property instance class Xamarin.Forms.IListProxy ListProxy" />
+      <MemberType>Property</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>Xamarin.Forms.IListProxy</ReturnType>
+      </ReturnValue>
+      <Docs>
+        <summary>To be added.</summary>
+        <value>To be added.</value>
+        <remarks>To be added.</remarks>
+      </Docs>
+    </Member>
     <Member MemberName="Name">
       <MemberSignature Language="C#" Value="public string Name { get; set; }" />
       <MemberSignature Language="ILAsm" Value=".property instance string Name" />