Adds a null check for Xamarin.Forms.Platform.Android.PageRenderer.Xamarin.Forms.Platform.Android.IOrderedTraversalController.UpdateTraversalOrder (#7050)

* Fixes #7049

* Test?

* Tap View please

* Spacing

* Address comments

* Excuse me, semicolons

* Remove private

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7049.cs

@@ -0,0 +1,58 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using NUnit.Framework;
+using Xamarin.UITest;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve (AllMembers=true)]
+	[Issue (IssueTracker.Github, 7049, "Null reference exception on some Android devices - Xamarin.Forms.Platform.Android.PageRenderer.Xamarin.Forms.Platform.Android.IOrderedTraversalController.UpdateTraversalOrder", PlatformAffected.Android)]
+	public class Issue7049 : TestContentPage
+	{
+		const string ContinueButton = "ContinueButton";
+		const string View1 = "View1";
+		const string View2 = "View2";
+		const string View3 = "View3";
+		
+		bool _flag = true;
+
+		protected override void Init()
+		{
+
+			var button = new Button { AutomationId = ContinueButton, Text = "Continue" };
+			button.Clicked += (_, __) =>
+			{
+				var view = _flag ?
+					(View)new Entry { AutomationId = View2, Text = "Press 1 time to crash" } :
+					new Label { AutomationId = View3, Text = "I'm shown, bug fixed!" };
+				_flag ^= true;
+				(Content as StackLayout).Children[1] = view;
+			};
+			Content = new StackLayout
+			{
+				Children =
+				{
+					button,
+					new Label { AutomationId = View1, Text = "Press 2 times to crash" }
+				}
+			};
+		}
+
+#if UITEST && __ANDROID__
+		[Test]
+		[Description ("Test null reference in IOrderedTraversalController.UpdateTraversalOrder of Android PageRenderer")]
+		public void Issue7049TestsNullRefInUpdateTraversalOrder()
+		{
+			RunningApp.WaitForElement(View1);
+			RunningApp.Tap(ContinueButton);
+			RunningApp.WaitForElement(View2);
+			RunningApp.Tap(ContinueButton);
+			RunningApp.WaitForElement(View3);
+			RunningApp.Tap(ContinueButton);
+		}
+#endif
+	}
+}

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

@@ -22,6 +22,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue6644.xaml.cs">
       <SubType>Code</SubType>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)Issue7049.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ShellGestures.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ShellInsets.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)CollectionViewGrouping.cs" />

Xamarin.Forms.Platform.Android/Renderers/PageRenderer.cs

@@ -187,7 +187,7 @@ namespace Xamarin.Forms.Platform.Android
 						!(
 							child is VisualElement ve && ve.IsTabStop
 							&& AutomationProperties.GetIsInAccessibleTree(ve) != false // accessible == true
-							&& ve.GetRenderer().View is ITabStop tabStop)
+							&& ve.GetRenderer()?.View is ITabStop tabStop)
 						 )
 						continue;
 
@@ -218,4 +218,4 @@ namespace Xamarin.Forms.Platform.Android
 			OrderedTraversalController.UpdateTraversalOrder();
 		}
 	}
-}
+}