Check ItemsSource for null in ListViewRenderer; fixes #2929 (#2934)

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue2929.cs

@@ -0,0 +1,113 @@
+using System.Collections.Generic;
+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.ListView)]
+#endif
+
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 2929, "[UWP] ListView with null ItemsSource crashes on 3.0.0.530893", 
+		PlatformAffected.UWP)]
+	public class Issue2929 : TestContentPage
+	{
+		const string Success = "Success";
+
+		protected override void Init()
+		{
+			var lv = new ListView();
+
+			var instructions = new Label { Text = $"If the '{Success}' label is visible, this test has passed." };
+
+			Content = new StackLayout
+			{
+				Children =
+				{
+					instructions,
+					new Label { Text = Success },
+					lv
+				}
+			};
+		}
+
+#if UITEST
+		[Test]
+		public void NullItemSourceDoesNotCrash()
+		{
+			// If we can see the Success label, it means we didn't crash. 
+			RunningApp.WaitForElement(Success);
+		}
+#endif
+	}
+
+#if UITEST
+	[Category(UITestCategories.ListView)]
+#endif
+
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.None, 99, "Make sure setting ItemSource to null doesn't blow up", 
+		PlatformAffected.UWP)]
+	public class SetListViewItemSourceToNull : TestContentPage
+	{
+		const string Success = "Success";
+		const string Go = "Go";
+
+		protected override void Init()
+		{
+			var lv = new ListView();
+			var itemSource = new List<string>
+			{
+				"One",
+				"Two",
+				"Three"
+			};
+			lv.ItemsSource = itemSource;
+
+			var result = new Label();
+
+			var button = new Button { Text = Go };
+
+			button.Clicked += (sender, args) =>
+			{
+				lv.ItemsSource = null;
+				result.Text = Success;
+			};
+
+			var instructions = new Label
+			{
+				Text = $"Tap the '{Go}' button. If the '{Success}' label is visible, this test has passed."
+			};
+
+			Content = new StackLayout
+			{
+				Children =
+				{
+					instructions,
+					button,
+					result,
+					lv
+				}
+			};
+		}
+
+#if UITEST
+		[Test]
+		public void SettingItemsSourceToNullDoesNotCrash()
+		{
+			RunningApp.WaitForElement(Go);
+			RunningApp.Tap(Go);
+
+			// If we can see the Success label, it means we didn't crash. 
+			RunningApp.WaitForElement(Success);
+		}
+#endif
+	}
+}

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

@@ -299,6 +299,7 @@
       <SubType>Code</SubType>
     </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue2681.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue2929.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue2983.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue2963.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue2981.cs" />

Xamarin.Forms.Platform.UAP/ListViewRenderer.cs

@@ -25,8 +25,8 @@ namespace Xamarin.Forms.Platform.UWP
 	public class ListViewRenderer : ViewRenderer<ListView, FrameworkElement>
 	{
 		ITemplatedItemsView<Cell> TemplatedItemsView => Element;
-		ObservableCollection<object> SourceItems => context?.Source as ObservableCollection<object>;
-		CollectionViewSource context;
+		ObservableCollection<object> SourceItems => _context?.Source as ObservableCollection<object>;
+		CollectionViewSource _context;
 		bool _itemWasClicked;
 		bool _subscribedToItemClick;
 		bool _subscribedToTapped;
@@ -83,12 +83,17 @@ namespace Xamarin.Forms.Platform.UWP
 
 		void ReloadData()
 		{
+			if (Element?.ItemsSource == null)
+			{
+				return;
+			}
+
 			var allSourceItems = new ObservableCollection<object>();
 			foreach (var item in Element.ItemsSource)
 				allSourceItems.Add(item);
 
 			// WinRT throws an exception if you set ItemsSource directly to a CVS, so bind it.
-			List.DataContext = context = new CollectionViewSource
+			List.DataContext = _context = new CollectionViewSource
 			{
 				Source = allSourceItems,
 				IsSourceGrouped = Element.IsGroupingEnabled
@@ -269,6 +274,11 @@ namespace Xamarin.Forms.Platform.UWP
 
 		void UpdateGrouping()
 		{
+			if (Element?.ItemsSource == null)
+			{
+				return;
+			}
+
 			bool grouping = Element.IsGroupingEnabled;
 
 			((CollectionViewSource)List.DataContext).IsSourceGrouped = grouping;