[Android] fixes ListView pull-to-refresh gesture in non-data areas (#5417) fixes #5268

* [Android] fixes ListView pull-to-refresh gesture in non-data areas

* refactoring

* addressing comments

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue5268.xaml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Xamarin.Forms.Controls.Issues.Issue5268">
+    <ListView x:Name="MyListView"
+              IsPullToRefreshEnabled="True"
+              IsRefreshing="{Binding IsBusy, Mode=OneWay}"
+              ItemsSource="{Binding Sources}"
+              BackgroundColor="Blue"
+              RefreshCommand="{Binding Command}" RowHeight="100">
+        <ListView.ItemTemplate>
+            <DataTemplate>
+                <ViewCell>
+                    <ScrollView>
+                        <StackLayout>
+                            <Label Text="{Binding Val}" MaxLines="100" HorizontalTextAlignment="Center" TextColor="White" FontSize="14" />
+                            <Label Text="{Binding Val}" MaxLines="100" HorizontalTextAlignment="Center" TextColor="White" FontSize="14" />
+                            <Label Text="{Binding Val}" MaxLines="100" HorizontalTextAlignment="Center" TextColor="White" FontSize="14" />
+                            <Label Text="{Binding Val}" MaxLines="100" HorizontalTextAlignment="Center" TextColor="White" FontSize="14" />
+                            <Label Text="{Binding Val}" MaxLines="100" HorizontalTextAlignment="Center" TextColor="White" FontSize="14" />
+                        </StackLayout>
+                    </ScrollView>
+                </ViewCell>
+            </DataTemplate>
+        </ListView.ItemTemplate>
+    </ListView>
+</ContentPage>

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue5268.xaml.cs

@@ -0,0 +1,42 @@
+#if APP
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Windows.Input;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 5268, "ListView with PullToRefresh enabled gestures conflict", PlatformAffected.Android)]
+	public partial class Issue5268 : ContentPage
+	{
+		[Preserve(AllMembers = true)]
+		public class SrcItem
+		{
+			public string Val { get; set; }
+		}
+
+		string GenerateLongString() => string.Join(" \n", Enumerable.Range(0, 50).Select(i => $"{Sources.Count} item"));
+
+		public ObservableCollection<SrcItem> Sources { get; }
+		public ICommand Command { get; }
+
+		public Issue5268()
+		{
+			InitializeComponent();
+			Sources = new ObservableCollection<SrcItem>();
+			Command = new Command(AddData);
+			Sources.Add(new SrcItem { Val = GenerateLongString() });
+			MyListView.BindingContext = this;
+		}
+
+		void AddData()
+		{
+			IsBusy = true;
+			Sources.Add(new SrcItem { Val = GenerateLongString() });
+			IsBusy = false;
+		}
+	}
+}
+#endif

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

@@ -434,6 +434,10 @@
       <DependentUpon>Issue5003.xaml</DependentUpon>
       <SubType>Code</SubType>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)Issue5268.xaml.cs">
+      <DependentUpon>Issue5268.xaml</DependentUpon>
+      <SubType>Code</SubType>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)LegacyComponents\NonAppCompatSwitch.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)MapsModalCrash.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ModalActivityIndicatorTest.cs" />
@@ -1119,4 +1123,10 @@
       <Generator>MSBuild:Compile</Generator>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue5268.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </EmbeddedResource>
+  </ItemGroup>
 </Project>

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

@@ -9,6 +9,7 @@ using Xamarin.Forms.Internals;
 using System;
 using Xamarin.Forms.PlatformConfiguration.AndroidSpecific;
 using Android.Widget;
+using Android.Runtime;
 
 namespace Xamarin.Forms.Platform.Android
 {
@@ -102,6 +103,9 @@ namespace Xamarin.Forms.Platform.Android
 			return new Size(40, 40);
 		}
 
+		protected virtual SwipeRefreshLayout CreateNativePullToRefresh(Context context)
+			=> new SwipeRefreshLayoutWithFixedNestedScrolling(context);
+
 		protected override void OnAttachedToWindow()
 		{
 			base.OnAttachedToWindow();
@@ -154,9 +158,9 @@ namespace Xamarin.Forms.Platform.Android
 					nativeListView = CreateNativeControl();
 					if (Forms.IsLollipopOrNewer)
 						nativeListView.NestedScrollingEnabled = true;
-					_refresh = new SwipeRefreshLayout(ctx);
+					_refresh = CreateNativePullToRefresh(ctx);
 					_refresh.SetOnRefreshListener(this);
-					_refresh.AddView(nativeListView, LayoutParams.MatchParent);
+					_refresh.AddView(nativeListView, new LayoutParams(LayoutParams.MatchParent, LayoutParams.MatchParent));
 					SetNativeControl(nativeListView, _refresh);
 
 					_headerView = new Container(ctx);
@@ -523,5 +527,54 @@ namespace Xamarin.Forms.Platform.Android
 				SetMeasuredDimension(widthSpec, heightSpec);
 			}
 		}
+
+		class SwipeRefreshLayoutWithFixedNestedScrolling : SwipeRefreshLayout
+		{
+			float _touchSlop;
+			float _initialDownY;
+			bool _nestedScrollAccepted;
+			bool _nestedScrollCalled;
+
+			public SwipeRefreshLayoutWithFixedNestedScrolling(Context ctx) : base(ctx)
+			{
+				_touchSlop = ViewConfiguration.Get(ctx).ScaledTouchSlop;
+			}
+
+			public override bool OnInterceptTouchEvent(MotionEvent ev)
+			{
+				if (ev.Action == MotionEventActions.Down)
+					_initialDownY = ev.GetAxisValue(Axis.Y);
+
+				var isBeingDragged = base.OnInterceptTouchEvent(ev);
+
+				if (!isBeingDragged && ev.Action == MotionEventActions.Move && _nestedScrollAccepted && !_nestedScrollCalled)
+				{
+					var y = ev.GetAxisValue(Axis.Y);
+					var dy = (y - _initialDownY) / 2;
+					isBeingDragged = dy > _touchSlop;
+				}
+
+				return isBeingDragged;
+			}
+
+			public override void OnNestedScrollAccepted(AView child, AView target, [GeneratedEnum] ScrollAxis axes)
+			{
+				base.OnNestedScrollAccepted(child, target, axes);
+				_nestedScrollAccepted = true;
+				_nestedScrollCalled = false;
+			}
+
+			public override void OnStopNestedScroll(AView child)
+			{
+				base.OnStopNestedScroll(child);
+				_nestedScrollAccepted = false;
+			}
+
+			public override void OnNestedScroll(AView target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed)
+			{
+				base.OnNestedScroll(target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed);
+				_nestedScrollCalled = true;
+			}
+		}
 	}
 }