Add workaround so ItemsRepeater doesn't leak the result of DataTemplate::Load

dev/Repeater/APITests/RepeaterTests.cs

@@ -30,6 +30,9 @@
 using System.Threading;
 using System.Collections.Generic;
 using Windows.UI.Xaml.Tests.MUXControls.ApiTests.RepeaterTests.Common.Mocks;
+using Windows.UI.Xaml.Tests.MUXControls.ApiTests.RepeaterTests.Common;
+using Windows.UI.Composition;
+using System.Threading.Tasks;
 
 namespace Windows.UI.Xaml.Tests.MUXControls.ApiTests.RepeaterTests
 {
@@ -609,5 +612,62 @@ public void VerifyUIElementsInItemsSource()
                 }
             });
         }
+
+        [TestMethod]
+        public void VerifyRepeaterDoesNotLeakItemContainers()
+        {
+            ObservableCollection<int> items = new ObservableCollection<int>();
+            for(int i=0;i<10;i++)
+            {
+                items.Add(i);
+            }
+
+            ItemsRepeater repeater = null;
+
+            RunOnUIThread.Execute(() =>
+            {
+                var template = (DataTemplate)XamlReader.Load("<DataTemplate xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation' "
+                    + "xmlns:local='using:MUXControlsTestApp.Samples'>"
+                    + "<local:DisposableUserControl Number='{Binding}'/>" 
+                    + "</DataTemplate>");
+                Verify.IsNotNull(template);
+                Verify.AreEqual(0, MUXControlsTestApp.Samples.DisposableUserControl.OpenItems, "Verify we start with 0 DisposableUserControl");
+
+                repeater = new ItemsRepeater() {
+                    ItemsSource = items,
+                    ItemTemplate = template,
+                    VerticalAlignment = VerticalAlignment.Top,
+                    HorizontalAlignment = HorizontalAlignment.Left
+                };
+
+                Content = repeater;
+
+            });
+
+            IdleSynchronizer.Wait();
+            // Wait until the Tick to make sure all layout has completed.
+            RunOnUIThread.WaitForTick();
+
+            RunOnUIThread.Execute(() =>
+            {
+
+                Verify.IsGreaterThanOrEqual(MUXControlsTestApp.Samples.DisposableUserControl.OpenItems, 10, "Verify we created at least 10 DisposableUserControl");
+
+                // Clear out the repeater and make sure everything gets cleaned up.
+                Content = null;
+                repeater = null;
+            });
+
+            IdleSynchronizer.Wait();
+            // Wait until the Tick to make sure all layout has completed.
+            RunOnUIThread.WaitForTick();
+
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
+            GC.Collect();
+
+            Verify.AreEqual(0, MUXControlsTestApp.Samples.DisposableUserControl.OpenItems, "Verify we cleaned up all the DisposableUserControl that were created");
+        }
+
     }
 }

dev/Repeater/ItemsRepeater.cpp

@@ -621,7 +621,17 @@ void ItemsRepeater::OnItemTemplateChanged(const winrt::IElementFactory& oldValue
         if (auto dataTemplate = newValue.try_as<winrt::DataTemplate>())
         {
             m_itemTemplateWrapper = winrt::make<ItemTemplateWrapper>(dataTemplate);
-            if (!dataTemplate.LoadContent().as<winrt::FrameworkElement>()) {
+            if (auto content = dataTemplate.LoadContent().as<winrt::FrameworkElement>())
+            {
+                // Due to bug https://github.com/microsoft/microsoft-ui-xaml/issues/3057, we need to get the framework
+                // to take ownership of the extra implicit ref that was returned by LoadContent. The simplest way to do
+                // this is to add it to a Children collection and immediately remove it.
+                auto children = Children();
+                children.Append(content);
+                children.RemoveAtEnd();
+            }
+            else
+            {
                 // We have a DataTemplate which is empty, so we need to set it to true
                 m_isItemTemplateEmpty = true;
             }

dev/Repeater/TestUI/Repeater_TestUI.projitems

@@ -19,6 +19,10 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
+    <Page Include="$(MSBuildThisFileDirectory)Samples\ItemTemplateSamples\DisposableUserControl.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
     <Page Include="$(MSBuildThisFileDirectory)Samples\LayoutSamples\VirtualLayoutPages\ActivityFeedSamplePage.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
@@ -112,6 +116,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)Samples\ItemsSourceSamples\SortingAndFilteringPage.xaml.cs">
       <DependentUpon>SortingAndFilteringPage.xaml</DependentUpon>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)Samples\ItemTemplateSamples\DisposableUserControl.xaml.cs">
+      <DependentUpon>DisposableUserControl.xaml</DependentUpon>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Samples\LayoutSamples\VirtualLayoutPages\ActivityFeedLayout.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Samples\LayoutSamples\VirtualLayoutPages\ActivityFeedSamplePage.xaml.cs">
       <DependentUpon>ActivityFeedSamplePage.xaml</DependentUpon>

dev/Repeater/TestUI/Samples/ItemTemplateSamples/DisposableUserControl.xaml

@@ -0,0 +1,14 @@
+<UserControl
+    x:Class="MUXControlsTestApp.Samples.DisposableUserControl"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    mc:Ignorable="d"
+    d:DesignHeight="300"
+    d:DesignWidth="400">
+
+    <Grid>
+        <TextBlock Text="{x:Bind Number}"/>
+    </Grid>
+</UserControl>

dev/Repeater/TestUI/Samples/ItemTemplateSamples/DisposableUserControl.xaml.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices.WindowsRuntime;
+using System.Threading;
+using Windows.Foundation;
+using Windows.Foundation.Collections;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Controls.Primitives;
+using Windows.UI.Xaml.Data;
+using Windows.UI.Xaml.Input;
+using Windows.UI.Xaml.Media;
+using Windows.UI.Xaml.Navigation;
+
+// The User Control item template is documented at https://go.microsoft.com/fwlink/?LinkId=234236
+
+namespace MUXControlsTestApp.Samples
+{
+    public sealed partial class DisposableUserControl : UserControl
+    {
+
+        public int Number
+        {
+            get { return (int)GetValue(NumberProperty); }
+            set { SetValue(NumberProperty, value); }
+        }
+
+        public static readonly DependencyProperty NumberProperty =
+            DependencyProperty.Register("Number", typeof(int), typeof(DisposableUserControl), new PropertyMetadata(-1));
+
+
+        public static int OpenItems { get { return _counter; } }
+        private static int _counter = 0;
+
+        public DisposableUserControl()
+        {
+            Interlocked.Increment(ref _counter);
+            this.InitializeComponent();
+        }
+
+        ~DisposableUserControl()
+        {
+            Interlocked.Decrement(ref _counter);
+        }
+    }
+}

dev/Repeater/TestUI/Samples/ItemTemplateSamples/ItemTemplateDemo.xaml

@@ -16,6 +16,7 @@
             <ColumnDefinition Width="auto" />
             <ColumnDefinition Width="auto" />
             <ColumnDefinition Width="auto" />
+            <ColumnDefinition Width="auto" />
         </Grid.ColumnDefinitions>
         <StackPanel>
             <TextBlock>DataTemplate Sample:</TextBlock>
@@ -80,7 +81,7 @@
             <TextBlock>ElementFactory Multiple Template Sample:</TextBlock>
             <controls:ItemsRepeaterScrollHost Height="400" Width="150">
                 <ScrollViewer>
-                    <controls:ItemsRepeater x:Name="repeater3" 
+                    <controls:ItemsRepeater x:Name="repeater4" 
                                             ItemsSource="{x:Bind Data}"
                                             Layout="{StaticResource stackLayout}">
                         <controls:ItemsRepeater.ItemTemplate>
@@ -99,5 +100,21 @@
                 </ScrollViewer>
             </controls:ItemsRepeaterScrollHost>
         </StackPanel>
+        <StackPanel Grid.Column="4">
+            <TextBlock>DataTemplate clear count checking:</TextBlock>
+            <controls:ItemsRepeaterScrollHost Height="400" Width="150">
+                <ScrollViewer>
+                    <controls:ItemsRepeater x:Name="repeater3" 
+                                            ItemsSource="{x:Bind Numbers}"
+                                            Layout="{StaticResource stackLayout}">
+                        <controls:ItemsRepeater.ItemTemplate>
+                            <DataTemplate x:DataType="local:MyData" >
+                                <local:DisposableUserControl Number="{x:Bind number}"/>
+                            </DataTemplate>
+                        </controls:ItemsRepeater.ItemTemplate>
+                    </controls:ItemsRepeater>
+                </ScrollViewer>
+            </controls:ItemsRepeaterScrollHost>
+        </StackPanel>
     </Grid>
 </Page>

dev/Repeater/TestUI/Samples/ItemTemplateSamples/ItemTemplateDemo.xaml.cs

@@ -13,10 +13,18 @@ namespace MUXControlsTestApp.Samples
 {
     public sealed partial class ItemTemplateDemo : Page
     {
-        public List<int> Data { get; set; } 
+        public List<int> Data { get; set; }
+        public List<MyData> Numbers = new List<MyData>();
+
         public ItemTemplateDemo()
         {
             Data = Enumerable.Range(0, 1000).ToList();
+
+            for(int i=0;i<10;i++)
+            {
+                Numbers.Add(new MyData(i));
+            }
+
             this.InitializeComponent();
         }
 
@@ -26,6 +34,16 @@ private void OnSelectTemplateKey(RecyclingElementFactory sender, SelectTemplateE
         }
     }
 
+    public class MyData
+    {
+        public int number;
+
+        public MyData(int number)
+        {
+            this.number = number;
+        }
+    }
+
     public class MySelector: DataTemplateSelector
     {
         public DataTemplate TemplateOdd { get; set; }

test/MUXControlsTestApp/Utilities/RunOnUIThread.cs

@@ -90,19 +90,26 @@ public static void Execute(CoreApplicationView whichView, Action action)
             }
         }
 
-        public async Task WaitForTick()
+        public static void WaitForTick()
         {
-            var renderingEventFired = new TaskCompletionSource<object>();
+            var renderingEvent = new ManualResetEvent(false);
 
-            EventHandler<object> renderingCallback = (sender, arg) =>
+            EventHandler<object> renderingHandler = (object sender, object args) =>
             {
-                renderingEventFired.TrySetResult(null);
+                renderingEvent.Set();
             };
-            CompositionTarget.Rendering += renderingCallback;
 
-            await renderingEventFired.Task;
+            RunOnUIThread.Execute(() =>
+            {
+                Windows.UI.Xaml.Media.CompositionTarget.Rendering += renderingHandler;
+            });
+
+            renderingEvent.WaitOne();
 
-            CompositionTarget.Rendering -= renderingCallback;
+            RunOnUIThread.Execute(() =>
+            {
+                Windows.UI.Xaml.Media.CompositionTarget.Rendering -= renderingHandler;
+            });
         }
 
     }