[Android] Prevent bubbled gestures from falling through transparent containers (#3091) fixes #2858

* [Android] Prevent bubbled gestures from falling through to controls behind transparent containers;
fixes #2858

* Remove XAMLC attribute

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue2858.xaml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<controls:TestContentPage xmlns="http://xamarin.com/schemas/2014/forms"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+			 xmlns:controls="clr-namespace:Xamarin.Forms.Controls;assembly=Xamarin.Forms.Controls"
+             x:Class="Xamarin.Forms.Controls.Issues.Issue2858">
+    <ContentPage.Content>
+		<Grid>
+			
+			<Grid.RowDefinitions>
+				<RowDefinition Height="Auto" ></RowDefinition>
+				<RowDefinition Height="Auto" ></RowDefinition>
+				<RowDefinition Height="*" ></RowDefinition>
+			</Grid.RowDefinitions>
+
+			<Label Text="Tap the red box below. Then tap the green area outside the box. If 'Success' is visible below, this test has passed."></Label>
+
+			<Label Grid.Row="1" Text="Running..." x:Name="Result"></Label>
+
+			<Grid Grid.Row="2" BackgroundColor="Blue" VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand" 
+				AutomationId="TapGrid">
+				<Grid.GestureRecognizers>
+					<TapGestureRecognizer Tapped="TapGestureRecognizer_OnTapped" />
+				</Grid.GestureRecognizers>
+			</Grid>
+			<Grid Grid.Row="2" RowSpacing="0" ColumnSpacing="0" InputTransparent="True" CascadeInputTransparent="False"
+				Padding="10" BackgroundColor="Green" AutomationId="OuterGrid">
+				<Grid BackgroundColor="Red"  HorizontalOptions="Center" WidthRequest="300" VerticalOptions="Center"
+					HeightRequest="300" AutomationId="InnerGrid">
+					
+				</Grid>
+			</Grid>
+		</Grid>
+    </ContentPage.Content>
+</controls:TestContentPage>

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue2858.xaml.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Xamarin.Forms;
+
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using Xamarin.Forms.Xaml;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.InputTransparent)]
+	[Category(UITestCategories.Gestures)]
+#endif
+
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 2858, "Transparency Cascading", PlatformAffected.Android)]
+	public partial class Issue2858 : TestContentPage
+	{
+		const string Success = "Success";
+		const string Failure = "Fail";
+		const string InnerGrid = "InnerGrid";
+		const string OuterGrid = "OuterGrid";
+
+#pragma warning disable CS0414
+		int _tapCount = 0;
+#pragma warning restore CS0414
+
+		public Issue2858 ()
+		{
+#if APP
+			InitializeComponent ();
+#endif
+		}
+
+#if APP
+		void TapGestureRecognizer_OnTapped(object sender, EventArgs e)
+		{
+			_tapCount += 1;
+
+			if (_tapCount == 1)
+			{
+				Result.Text = Success;
+			}
+			else
+			{
+				Result.Text = Failure;
+			}
+		}
+#endif
+
+		protected override void Init()
+		{
+			
+		}
+
+
+#if UITEST
+		[Test]
+		public void CascadeInputTransparentGrids()
+		{
+			RunningApp.WaitForElement(InnerGrid);
+			RunningApp.Tap(InnerGrid);
+
+			var green = RunningApp.WaitForElement(OuterGrid);
+			RunningApp.TapCoordinates(green[0].Rect.CenterX, green[0].Rect.Y + 20);
+
+			RunningApp.WaitForElement(Success);
+		}
+#endif
+	}
+}

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

@@ -328,6 +328,10 @@
       <SubType>Code</SubType>
     </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue2681.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue2858.xaml.cs">
+      <DependentUpon>Issue2858.xaml</DependentUpon>
+      <SubType>Code</SubType>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue2929.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue2983.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue2963.cs" />
@@ -929,4 +933,10 @@
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
   </ItemGroup>
-</Project>
+  <ItemGroup>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue2858.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </EmbeddedResource>
+  </ItemGroup>
+</Project>

Xamarin.Forms.Platform.Android/Platform.cs

@@ -1156,7 +1156,7 @@ namespace Xamarin.Forms.Platform.Android
 
 		internal class DefaultRenderer : VisualElementRenderer<View>
 		{
-			bool _notReallyHandled;
+			public bool NotReallyHandled { get; private set; }
 			IOnTouchListener _touchListener;
 
 			[Obsolete("This constructor is obsolete as of version 2.5. Please use DefaultRenderer(Context) instead.")]
@@ -1173,7 +1173,7 @@ namespace Xamarin.Forms.Platform.Android
 
 			internal void NotifyFakeHandling()
 			{
-				_notReallyHandled = true;
+				NotReallyHandled = true;
 			}
 
 			public override bool OnTouchEvent(MotionEvent e)
@@ -1216,11 +1216,11 @@ namespace Xamarin.Forms.Platform.Android
 				// it then knows to ignore that result and return false/unhandled. This allows the event to propagate up the tree.
 				#endregion
 
-				_notReallyHandled = false;
+				NotReallyHandled = false;
 
 				var result = base.DispatchTouchEvent(e);
 
-				if (result && _notReallyHandled)
+				if (result && NotReallyHandled)
 				{
 					// If the child control returned true from its touch event handler but signalled that it was a fake "true", then we
 					// don't consider the event truly "handled" yet. 

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

@@ -9,13 +9,13 @@ namespace Xamarin.Forms.Platform.Android
 
 		public bool HandleMotionEvent(IViewParent parent, MotionEvent motionEvent)
 		{
-			if (_isInViewCell || _element.InputTransparent || motionEvent.Action == MotionEventActions.Cancel)
+			if (_isInViewCell || motionEvent.Action == MotionEventActions.Cancel)
 			{
 				return false;
 			}
 
 			var renderer = parent as Platform.DefaultRenderer;
-			if (renderer == null)
+			if (renderer == null || ShouldPassThroughElement())
 			{
 				return false;
 			}
@@ -40,5 +40,45 @@ namespace Xamarin.Forms.Platform.Android
 			// we don't fake handle the events because ListView needs them for row selection
 			_isInViewCell = element.IsInViewCell();
 		}
+
+		bool ShouldPassThroughElement()
+		{
+			if (_element is Layout layout)
+			{
+				if (!layout.InputTransparent)
+				{
+					// If the layout is not input transparent, then the event should not pass through it
+					return false;
+				}
+
+				if (layout.CascadeInputTransparent)
+				{
+					// This is a layout, and it's transparent, and all its children are transparent, then the event
+					// can just pass through 
+					return true;
+				}
+
+				if (Platform.GetRenderer(_element) is Platform.DefaultRenderer renderer)
+				{
+					// If the event is being bubbled up from a child which is not inputtransparent, we do not want
+					// it to be passed through (just up the tree)
+					if (renderer.NotReallyHandled)
+					{
+						return false;
+					}
+				}
+
+				// This event isn't being bubbled up by a non-InputTransparent child layout
+				return true;
+			}
+
+			if (_element.InputTransparent)
+			{
+				// This is not a layout and it's transparent; the event can just pass through 
+				return true;
+			}
+
+			return false;
+		}
 	}
 }

Xamarin.Forms.Platform.Android/VisualElementRenderer.cs

@@ -21,7 +21,7 @@ namespace Xamarin.Forms.Platform.Android
 		string _defaultContentDescription;
 		bool? _defaultFocusable;
 		string _defaultHint;
-		bool _inputTransparentInherited = true;
+		bool _cascadeInputTransparent = true;
 
 		VisualElementPackager _packager;
 		PropertyChangedEventHandler _propertyChangeHandler;
@@ -52,7 +52,7 @@ namespace Xamarin.Forms.Platform.Android
 
 		public override bool DispatchTouchEvent(MotionEvent e)
 		{
-			if (InputTransparent && _inputTransparentInherited)
+			if (InputTransparent && _cascadeInputTransparent)
 			{
 				// If the Element is InputTransparent, this ViewGroup will be marked InputTransparent
 				// If we're InputTransparent and our transparency should be applied to our child controls,
@@ -339,7 +339,7 @@ namespace Xamarin.Forms.Platform.Android
 				return;
 			}
 
-			_inputTransparentInherited = layout.CascadeInputTransparent;
+			_cascadeInputTransparent = layout.CascadeInputTransparent;
 		}
 
 		protected void SetPackager(VisualElementPackager packager)