fix(listview): [iOS] Fix container reuse by template

When ItemTemplateSelector is set, ensure list only reuses containers for items with the same template. This was previously failing because the native reuse identifier was being set degenerately.

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/CounterGrid.cs

@@ -22,6 +22,11 @@ internal partial class CounterGrid : Grid
 		public static int GlobalMeasureCount { get; private set; }
 		public static int GlobalArrangeCount { get; private set; }
 
+		/// <summary>
+		/// How many times has this instance been data-bound?
+		/// </summary>
+		public int LocalBindCount { get; private set; }
+
 		public int LocalMeasureCount { get; private set; }
 		public int LocalArrangeCount { get; private set; }
 
@@ -43,6 +48,7 @@ private void On_DataContextChanged(DependencyObject sender, DataContextChangedEv
 			if (args.NewValue != null)
 			{
 				BindCount++;
+				LocalBindCount++;
 				WasUpdated?.Invoke();
 			}
 		}
@@ -63,6 +69,9 @@ protected override Size ArrangeOverride(Size finalSize)
 			return base.ArrangeOverride(finalSize);
 		}
 
+		/// <summary>
+		/// Reset static counters.
+		/// </summary>
 		public static void Reset()
 		{
 			CreationCount = 0;

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_ListViewBase.cs

@@ -59,6 +59,10 @@ public partial class Given_ListViewBase
 		private DataTemplate SelectableItemTemplateB => _testsResources["SelectableItemTemplateB"] as DataTemplate;
 		private DataTemplate SelectableItemTemplateC => _testsResources["SelectableItemTemplateC"] as DataTemplate;
 
+		private DataTemplate RedSelectableTemplate => _testsResources["RedSelectableTemplate"] as DataTemplate;
+		private DataTemplate GreenSelectableTemplate => _testsResources["GreenSelectableTemplate"] as DataTemplate;
+		private DataTemplate BeigeSelectableTemplate => _testsResources["BeigeSelectableTemplate"] as DataTemplate;
+
 		[TestInitialize]
 		public void Init()
 		{
@@ -1443,6 +1447,79 @@ void InsertAnItem()
 			}
 		}
 
+		[TestMethod]
+		public async Task When_ItemTemplate_Selector_Correct_Reuse()
+		{
+			var selector = new KeyedTemplateSelector<ItemColor>(o => (o as ItemColorViewModel)?.ItemType ?? ItemColor.None)
+			{
+				Templates =
+				{
+					{ItemColor.Red, RedSelectableTemplate },
+					{ItemColor.Green, GreenSelectableTemplate},
+					{ItemColor.Beige, BeigeSelectableTemplate}
+				}
+			};
+
+			var source = new List<ItemColorViewModel>();
+			int itemNo = 0;
+			void AddItem(ItemColor itemType)
+			{
+				itemNo++;
+				source.Add(new ItemColorViewModel { ItemType = itemType, ItemIndex = itemNo });
+			}
+
+			AddItem(ItemColor.Red);
+			AddItem(ItemColor.Green);
+
+			for (int i = 0; i < 10; i++)
+			{
+				AddItem(ItemColor.Beige);
+			}
+
+			AddItem(ItemColor.Green);
+
+			var SUT = new ListView
+			{
+				Width = 180,
+				Height = 320,
+				ItemsSource = source,
+				ItemTemplateSelector = selector,
+				ItemsPanel = NoCacheItemsStackPanel,
+				ItemContainerStyle = NoSpaceContainerStyle
+			};
+
+			WindowHelper.WindowContent = SUT;
+			await WindowHelper.WaitForLoaded(SUT);
+
+			var redLeader = SUT.ContainerFromIndex(0) as ListViewItem;
+			var greenLeader = SUT.ContainerFromIndex(1) as ListViewItem;
+			var redGrid = redLeader.FindFirstChild<CounterGrid>();
+			var greenGrid = greenLeader.FindFirstChild<CounterGrid>();
+
+			var sv = SUT.FindFirstChild<ScrollViewer>();
+
+			sv.ChangeView(null, 100, null, disableAnimation: true);
+			await Task.Delay(20);
+
+			var redCount1 = redGrid.LocalBindCount;
+			var greenCount1 = greenGrid.LocalBindCount;
+
+			for (int i = 300; i < 1000; i += 300)
+			{
+				sv.ChangeView(null, i, null, disableAnimation: true);
+				await Task.Delay(20);
+			}
+
+
+			var redCount2 = redGrid.LocalBindCount;
+			var greenCount2 = greenGrid.LocalBindCount;
+
+			Assert.AreEqual(redCount1, redCount2); // Red template should not have been rebound
+			Assert.AreEqual(greenCount1 + 1, greenCount2); // Green template should be reused once for final item
+		}
+
+
+
 		private bool ApproxEquals(double value1, double value2) => Math.Abs(value1 - value2) <= 2;
 
 		private class When_Removed_From_Tree_And_Selection_TwoWay_Bound_DataContext : System.ComponentModel.INotifyPropertyChanged
@@ -1556,4 +1633,58 @@ protected override DataTemplate SelectTemplateCore(object item)
 			return template;
 		}
 	}
+
+	public class KeyedTemplateSelector<T> : DataTemplateSelector
+	{
+		private readonly Func<object, T> _keySelector;
+
+		public KeyedTemplateSelector(Func<object, T> keySelector = null)
+		{
+			this._keySelector = keySelector;
+		}
+
+		public IDictionary<T, DataTemplate> Templates { get; } = new Dictionary<T, DataTemplate>();
+
+		protected override DataTemplate SelectTemplateCore(object item, DependencyObject container) => SelectTemplateCore(item); // On UWP only this overload is called when eg Button.ContentTemplateSelector is set
+
+		protected override DataTemplate SelectTemplateCore(object item)
+		{
+			if (item == null)
+			{
+				return null;
+			}
+
+			T itemT;
+			if (_keySelector != null)
+			{
+				itemT = _keySelector(item);
+			}
+			else if (item is T)
+			{
+				itemT = (T)item;
+			}
+			else
+			{
+				return null;
+			}
+
+			var template = Templates.UnoGetValueOrDefault(itemT);
+			return template;
+		}
+	}
+
+	public enum ItemColor
+	{
+		None,
+		Red,
+		Green,
+		Beige
+	}
+
+	public class ItemColorViewModel
+	{
+		public ItemColor ItemType { get; set; }
+		public int ItemIndex { get; set; }
+		public string DisplayString => $"Item {ItemIndex}";
+	}
 }

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/TestsResources.xaml

@@ -3,9 +3,10 @@
 					xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 					xmlns:local="using:Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml_Controls"
 					xmlns:mux="using:Microsoft.UI.Xaml.Controls"
+					xmlns:xamarin="http://uno.ui/xamarin"
 					xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
 					xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-					mc:Ignorable="d">
+					mc:Ignorable="d xamarin">
 	<Style x:Key="BasicListViewContainerStyle"
 		   TargetType="ListViewItem">
 		<Setter Property="Template">
@@ -29,7 +30,8 @@
 			<Setter.Value>
 				<ControlTemplate TargetType="ListViewItem">
 					<ContentPresenter Content="{TemplateBinding Content}"
-									  ContentTemplate="{TemplateBinding ContentTemplate}" />
+									  ContentTemplate="{TemplateBinding ContentTemplate}"
+									  xamarin:ContentTemplateSelector="{TemplateBinding ContentTemplateSelector}" />
 				</ControlTemplate>
 			</Setter.Value>
 		</Setter>
@@ -215,4 +217,41 @@
 					   TextWrapping="Wrap" />
 		</Border>
 	</DataTemplate>
+
+	<DataTemplate x:Name="RedSelectableTemplate">
+		<Border Background="Red"
+				BorderBrush="DarkRed"
+				BorderThickness="2"
+				CornerRadius="5"
+				Height="95"
+				MinWidth="100">
+			<local:CounterGrid>
+				<TextBlock Text="{Binding DisplayString}" />
+			</local:CounterGrid>
+		</Border>
+	</DataTemplate>
+	<DataTemplate x:Name="GreenSelectableTemplate">
+		<Border Background="Green"
+				BorderBrush="DarkGreen"
+				BorderThickness="2"
+				CornerRadius="5"
+				Height="125"
+				MinWidth="100">
+			<local:CounterGrid>
+				<TextBlock Text="{Binding DisplayString}" />
+			</local:CounterGrid>
+		</Border>
+	</DataTemplate>
+	<DataTemplate x:Name="BeigeSelectableTemplate">
+		<Border Background="Beige"
+				BorderBrush="SaddleBrown"
+				BorderThickness="2"
+				CornerRadius="5"
+				Height="54"
+				MinWidth="100">
+			<local:CounterGrid>
+				<TextBlock Text="{Binding DisplayString}" />
+			</local:CounterGrid>
+		</Border>
+	</DataTemplate>
 </ResourceDictionary>

src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBaseSource.iOS.cs

@@ -642,7 +642,7 @@ private NSString GetReusableCellIdentifier(NSIndexPath indexPath)
 
 			if (!_templateCells.TryGetValue(template ?? _nullDataTemplateKey, out identifier))
 			{
-				identifier = new NSString(_templateCache.Count.ToString(CultureInfo.InvariantCulture));
+				identifier = new NSString(_templateCells.Count.ToString(CultureInfo.InvariantCulture));
 				_templateCells[template ?? _nullDataTemplateKey] = identifier;
 
 				Owner.RegisterClassForCell(typeof(ListViewBaseInternalContainer), identifier);