[All] Crash fixes for ListViews (#243)

* [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

2 files changed, 122 insertions, 0 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" />