[Controls] Add repo for issue #3275

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue3275.cs

@@ -0,0 +1,233 @@
+using System;
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Reflection;
+using System.Threading.Tasks;
+using System.Windows.Input;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 3275, "For ListView in Recycle mode ScrollTo causes cell leak and in some cases NRE", PlatformAffected.iOS)]
+	public class Issue3275 : TestContentPage // or TestMasterDetailPage, etc ...
+	{
+		static readonly string _btnLeakId = "btnLeak";
+		static readonly string _btnScrollToId = "btnScrollTo";
+
+		protected override void Init()
+		{
+			var layout = new StackLayout();
+
+			var btn = new Button
+			{
+				Text = " Leak 1 ",
+				AutomationId = _btnLeakId,
+				Command = new Command(() =>
+				{
+					Navigation.PushAsync(new Issue3275TransactionsPage1());
+				})
+			};
+			layout.Children.Add(btn);
+			Content = layout;
+		}
+
+
+
+		public class Issue3275TransactionsPage1 : ContentPage
+		{
+			private readonly TransactionsViewModel _viewModel = new TransactionsViewModel();
+			FastListView _transactionsListView;
+
+			public Issue3275TransactionsPage1()
+			{
+				var grd = new Grid();
+				grd.RowDefinitions.Add(new RowDefinition { Height = GridLength.Auto });
+				grd.RowDefinitions.Add(new RowDefinition { Height = GridLength.Auto });
+				grd.RowDefinitions.Add(new RowDefinition());
+				_transactionsListView = new FastListView
+				{
+					HasUnevenRows = true,
+					ItemTemplate = new DataTemplate(() =>
+					{
+						var viewCell = new ViewCell();
+						var item = new MenuItem
+						{
+							Text = "test"
+						};
+						item.SetBinding(MenuItem.CommandProperty, new Binding("BindingContext.RepeatCommand", source: _transactionsListView));
+						item.SetBinding(MenuItem.CommandParameterProperty, new Binding("."));
+						viewCell.ContextActions.Add(item);
+						var lbl = new Label();
+						lbl.SetBinding(Label.TextProperty, "Name");
+						viewCell.View = lbl;
+						return viewCell;
+					})
+				};
+				_transactionsListView.SetBinding(ListView.ItemsSourceProperty, "Items");
+
+				grd.Children.Add(new Label
+				{
+					Text = "Click 'Scroll To' and go back"
+				});
+
+				var btn = new Button
+				{
+					Text = "Scroll to",
+					AutomationId = _btnScrollToId,
+					Command = new Command(() =>
+					{
+						var item = _viewModel.Items.Skip(250).First();
+						_transactionsListView.ScrollTo(item, ScrollToPosition.MakeVisible, false);
+					})
+				};
+
+				Grid.SetRow(btn, 1);
+				grd.Children.Add(btn);
+				Grid.SetRow(_transactionsListView, 2);
+				grd.Children.Add(_transactionsListView);
+
+				Content = grd;
+
+
+				BindingContext = _viewModel;
+			}
+
+			protected override void OnDisappearing()
+			{
+				BindingContext = null; // IMPORTANT!!! Prism.Forms does this under the hood
+			}
+		}
+
+		public sealed class FastListView : ListView
+		{
+			public FastListView() : base(ListViewCachingStrategy.RecycleElement)
+			{
+			}
+		}
+
+		public class TransactionsViewModel
+		{
+			public TransactionsViewModel()
+			{
+				var items = Enumerable.Range(1, 500).Select(i => new Item { Name = i.ToString() });
+
+				Items = new ObservableCollection<Item>(items);
+
+				RepeatCommand = new AsyncDelegateCommand<object>(Repeat, x => true);
+			}
+
+			public ObservableCollection<Item> Items { get; }
+
+			public AsyncDelegateCommand<object> RepeatCommand { get; }
+
+			private Task Repeat(object item)
+			{
+				return Task.CompletedTask;
+			}
+		}
+
+		public class Item
+		{
+			public string Name { get; set; }
+		}
+
+		public sealed class AsyncDelegateCommand<T> : ICommand
+		{
+#pragma warning disable 0067
+			public event EventHandler CanExecuteChanged;
+#pragma warning restore 0067
+
+			private readonly Func<T, Task> _executeMethod;
+			private readonly Func<T, bool> _canExecuteMethod;
+			private bool _isInFlight;
+
+#if XAMARIN
+		private DateTime _lastExecuted = DateTime.MinValue;
+#endif
+
+			public AsyncDelegateCommand(Func<T, Task> executeMethod)
+				: this(executeMethod, _ => true)
+			{
+			}
+
+			public AsyncDelegateCommand(Func<T, Task> executeMethod, Func<T, bool> canExecuteMethod)
+			{
+				var genericTypeInfo = typeof(T).GetTypeInfo();
+
+				// DelegateCommand allows object or Nullable<>.  
+				// note: Nullable<> is a struct so we cannot use a class constraint.
+				if (genericTypeInfo.IsValueType)
+				{
+					if (!genericTypeInfo.IsGenericType || !typeof(Nullable<>).GetTypeInfo().IsAssignableFrom(genericTypeInfo.GetGenericTypeDefinition().GetTypeInfo()))
+						throw new InvalidCastException("T for DelegateCommand<T> is not an object nor Nullable.");
+				}
+
+				_executeMethod = executeMethod;
+				_canExecuteMethod = canExecuteMethod;
+			}
+
+			internal async Task Execute(T parameter)
+			{
+				if (_isInFlight)
+					return;
+
+#if XAMARIN
+			if (DateTime.UtcNow.Subtract(_lastExecuted).TotalMilliseconds < 200d)
+				return;
+#endif
+
+				try
+				{
+					_isInFlight = true;
+
+					await _executeMethod(parameter);
+				}
+				finally
+				{
+					_isInFlight = false;
+
+#if XAMARIN
+				_lastExecuted = DateTime.UtcNow;
+#endif
+				}
+			}
+
+			internal bool CanExecute(T parameter)
+			{
+				return _canExecuteMethod(parameter);
+			}
+
+			public void Execute(object parameter)
+			{
+				//Execute((T)parameter).NotWait();
+			}
+
+			public bool CanExecute(object parameter)
+			{
+				return CanExecute((T)parameter);
+			}
+		}
+
+#if UITEST
+		[Test]
+		public void Issue3275Test()
+		{
+			RunningApp.WaitForElement(q => q.Marked(_btnLeakId));
+			RunningApp.Tap(q => q.Marked(_btnLeakId));
+			RunningApp.WaitForElement(q => q.Marked(_btnScrollToId));
+			RunningApp.Tap(q => q.Marked(_btnScrollToId));
+			RunningApp.Back();
+			RunningApp.WaitForElement(q => q.Marked(_btnLeakId));
+		}
+
+
+#endif
+	}
+}

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

@@ -776,6 +776,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue3408.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue3413.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue3525.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue3275.cs" />
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Bugzilla22229.xaml">