From 4b19d49aa228330af37cee8c4d4fe7097eaf608d Mon Sep 17 00:00:00 2001
From: "E.Z. Hart" <hartez@users.noreply.github.com>
Date: Tue, 24 Jan 2017 04:48:36 -0700
Subject: [PATCH] Add check for disposed gesture detector on
 VisualElementRenderer (#706)

---
 .../Bugzilla45330.cs                               | 119 +++++++++++++++++++++
 .../Xamarin.Forms.Controls.Issues.Shared.projitems |   1 +
 .../VisualElementRenderer.cs                       |   6 ++
 3 files changed, 126 insertions(+)
 create mode 100644 Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla45330.cs

diff --git a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla45330.cs b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla45330.cs
new file mode 100644
index 0000000..d3a05fd
--- /dev/null
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla45330.cs
@@ -0,0 +1,119 @@
+using System;
+using System.Collections.ObjectModel;
+using System.Linq;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Bugzilla, 45330, "System.ObjectDisposedException: Cannot access a disposed object. Object name: 'Android.Views.GestureDetector'.", PlatformAffected.Android)]
+	public class Bugzilla45330 : TestContentPage 
+	{
+		ObservableCollection<_45330Notification> _feed;
+
+		[Preserve(AllMembers = true)]
+		public class _45330Dto
+		{
+			public _45330Dto()
+			{
+				Notifications = new ObservableCollection<_45330Notification>();
+			}
+
+			public ObservableCollection<_45330Notification> Notifications { get; set; }
+		}
+
+		[Preserve(AllMembers = true)]
+		public class _45330Notification
+		{
+			public string UniqueId { get; set; }
+			public DateTime DisplayDate { get; set; }
+		}
+
+		[Preserve(AllMembers = true)]
+		public class _45330ListCell : ViewCell
+		{
+			protected override void OnBindingContextChanged()
+			{
+				base.OnBindingContextChanged();
+
+				var item = BindingContext as _45330Notification;
+				if (item == null) return;
+
+				View = new StackLayout()
+				{
+					BackgroundColor = Color.Transparent,
+					Padding = new Thickness(0, 1, 0, 1),
+					Children = { new Label { Text = item.UniqueId } }
+				};
+			}
+		}
+
+		public ObservableCollection<_45330Notification> Feed
+		{
+			get { return _feed; }
+			set
+			{
+				_feed = value;
+				OnPropertyChanged();
+			}
+		}
+
+		protected override void Init()
+		{
+			BindingContext = this;
+			Feed = MakeNotifications();
+
+			var listview = new ListView();
+			listview.SetBinding(ListView.ItemsSourceProperty, "Feed");
+			listview.ItemTemplate = new DataTemplate(typeof(_45330ListCell));
+			listview.IsPullToRefreshEnabled = true;
+			listview.RefreshCommand = new Command(() =>
+			{
+				listview.IsRefreshing = false;
+				Feed = MakeNotifications();
+			});
+
+			listview.ItemAppearing += (sender, e) =>
+			{
+				var currentItem = e.Item as _45330Notification;
+				if (currentItem == null) return;
+				var item = Feed.Last();
+				if (currentItem.UniqueId == item.UniqueId)
+				{
+					Feed = MakeNotifications();
+				}
+			};
+
+			var layout = new StackLayout();
+
+			var instructions = new Label { Text = @"The bug can be intermittently reproduced by pulling the list down to refresh it and immediately tapping one of the cells. 
+Leaving this test page in for reference purposes, and possibly as a base for a future UI test if we get a way to accurately/consistently simulate the events which cause the crash."};
+			
+			layout.Children.Add(instructions);
+			layout.Children.Add(listview);
+
+			Content = layout;
+		}
+
+		ObservableCollection<_45330Notification> MakeNotifications()
+		{
+			var list = new _45330Dto();
+			for (int i = 0; i < 1000; i++)
+			{
+				list.Notifications.Add(new _45330Notification()
+				{
+					UniqueId = i.ToString(),
+					DisplayDate = DateTime.UtcNow
+				});
+			}
+			return list.Notifications;
+		}
+
+		protected override void OnAppearing()
+		{
+			base.OnAppearing();
+			Feed = MakeNotifications();
+		}
+	}
+}
\ No newline at end of file
diff --git a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
index ba7de6c..c459401 100644
--- a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
@@ -149,6 +149,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla42832.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla44044.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla44338.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Bugzilla45330.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla45743.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla46494.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla44476.cs" />
diff --git a/Xamarin.Forms.Platform.Android/VisualElementRenderer.cs b/Xamarin.Forms.Platform.Android/VisualElementRenderer.cs
index f67eb66..19b05e2 100644
--- a/Xamarin.Forms.Platform.Android/VisualElementRenderer.cs
+++ b/Xamarin.Forms.Platform.Android/VisualElementRenderer.cs
@@ -106,6 +106,12 @@ namespace Xamarin.Forms.Platform.Android
 
 			_gestureListener?.OnTouchEvent(e);
 
+			if (_gestureDetector.IsValueCreated && _gestureDetector.Value.Handle == IntPtr.Zero)
+			{
+				// This gesture detector has already been disposed, probably because it's on a cell which is going away
+				return handled;
+			}
+
 			return _gestureDetector.Value.OnTouchEvent(e) || handled;
 		}
 
-- 
2.7.4