[iOS/Android] Handle item selection highlight when ListView cell is tapped erratically (#520)

* Fix multi tap selection highlight

* added sample code

* add ios fix

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla32956.cs

@@ -0,0 +1,48 @@
+using System.Collections.Generic;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using System.Threading.Tasks;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Bugzilla, 32956, "Setting ListView.SelectedItem to null does not remove list item highlight when list item is tapped multiple times quickly", PlatformAffected.Android | PlatformAffected.iOS)]
+	public class Bugzilla32956 : TestNavigationPage
+	{
+		protected override void Init()
+		{
+			var list = new List<int>();
+			for(var i=0; i<10; i++)
+				list.Add(i);
+
+			var listView = new ListView
+			{
+				ItemsSource = list
+			};
+			listView.ItemSelected += async (sender, args) =>
+			{
+				if (args.SelectedItem == null)
+					return;
+
+				await Task.Delay(1000);
+				await Navigation.PushAsync(new ContentPage());
+			};
+
+			var contentPage = new ContentPage
+			{
+				Content = listView
+			};
+			contentPage.Appearing += (sender, args) =>
+			{
+				listView.SelectedItem = null;
+			};
+
+			PushAsync(contentPage);
+		}
+	}
+}

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

@@ -58,6 +58,7 @@
       <SubType>Code</SubType>
     </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla32847.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Bugzilla32956.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla33248.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla33268.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla33612.cs" />

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

@@ -371,8 +371,9 @@ namespace Xamarin.Forms.Platform.Android
 			if (position < 0 || position >= Count)
 				return;
 
+			if(_lastSelected != view)
+				_fromNative = true;
 			Select(position, view);
-			_fromNative = true;
 			Controller.NotifyRowTapped(position, cell);
 		}
 

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

@@ -914,7 +914,8 @@ namespace Xamarin.Forms.Platform.iOS
 
 				SetCellBackgroundColor(cell, UIColor.Clear);
 
-				_selectionFromNative = true;
+				if (!cell.Selected)
+					_selectionFromNative = true;
 
 				tableView.EndEditing(true);
 				Controller.NotifyRowTapped(indexPath.Section, indexPath.Row, formsCell);