Fixes various memory leaks in listview with group headers (#6761)

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue6761.xaml

@@ -0,0 +1,79 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<controls:TestContentPage xmlns:controls="clr-namespace:Xamarin.Forms.Controls"
+             xmlns="http://xamarin.com/schemas/2014/forms"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d"
+             x:Class="Xamarin.Forms.Controls.Issues.Issue6761">
+    <StackLayout>
+        <StackLayout Orientation="Horizontal">
+            <Button AutomationId="Issue6761Refresh" Clicked="RefreshItems" Text="Refresh" BackgroundColor="Cyan"/>
+            <Button AutomationId="Issue6761GC" Clicked="GCClick" Text="GC" BackgroundColor="Cyan"/>
+        </StackLayout>
+        <Label Text="Scroll the list, tap Refresh button a few times." />
+        <Label AutomationId="Issue6761Label" Text="{Binding DisposeString}"/>
+        <Label AutomationId="Issue6761Mem" Text="{Binding TotalMemory}"/>
+        <StackLayout Orientation="Horizontal">
+            <ListView
+                ItemsSource="{Binding ItemGroups}"
+                IsGroupingEnabled="True"
+                GroupDisplayBinding="{Binding GroupName}">
+                <ListView.ItemTemplate>
+                    <DataTemplate>
+                        <ViewCell>
+                            <StackLayout Margin="20">
+                                <Label Text="{Binding Name}" />
+                            </StackLayout>
+                        </ViewCell>
+                    </DataTemplate>
+                </ListView.ItemTemplate>
+            </ListView>
+            <ListView
+                ItemsSource="{Binding ItemGroups}"
+                IsGroupingEnabled="True">
+                <ListView.GroupHeaderTemplate>
+                    <DataTemplate>
+                        <ViewCell>
+                            <StackLayout Padding="15, 7, 15, 7" Orientation="Horizontal" BackgroundColor="#ffdab0">
+
+                                <Frame
+                                CornerRadius="14"
+                                BackgroundColor="#cf7806"
+                                Padding="2"
+                                Margin="0"
+                                HasShadow="false" >
+
+                                    <Frame
+                                    CornerRadius="12"
+                                    BackgroundColor="#ffdab0"
+                                    Padding="0"
+                                    Margin="0"
+                                    HasShadow="false" >
+
+                                        <Label
+                                        Text="{Binding GroupName}"
+                                        Margin="10, 5, 10, 5"
+                                        TextColor="#cf7806"
+                                        HorizontalTextAlignment="Center"
+                                        HorizontalOptions="Center"
+                                        VerticalTextAlignment="Center"
+                                        VerticalOptions="Center" />
+                                    </Frame>
+                                </Frame>
+                            </StackLayout>
+                        </ViewCell>
+                    </DataTemplate>
+                </ListView.GroupHeaderTemplate>
+                <ListView.ItemTemplate>
+                    <DataTemplate>
+                        <ViewCell>
+                            <StackLayout Margin="20">
+                                <Label Text="{Binding Name}" />
+                            </StackLayout>
+                        </ViewCell>
+                    </DataTemplate>
+                </ListView.ItemTemplate>
+            </ListView>
+        </StackLayout>
+    </StackLayout>
+</controls:TestContentPage>

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue6761.xaml.cs

@@ -0,0 +1,142 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using System;
+using System.Collections.ObjectModel;
+using System.Runtime.CompilerServices;
+using System.ComponentModel;
+using System.Collections.Generic;
+
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 6761, "Memory leak in ListView with group headers on IOS", PlatformAffected.Default)]
+	public partial class Issue6761 : TestContentPage
+	{
+		public Issue6761()
+		{
+#if APP
+			InitializeComponent();
+#endif
+			BindingContext = _viewModel = new ViewModelIssue6761();
+
+		}
+
+		protected override void Init()
+        {
+        }
+
+		int _count;
+		ViewModelIssue6761 _viewModel;
+		IList<WeakReference<ModelIssue6761Group>> _weakList = new List<WeakReference<ModelIssue6761Group>>();
+		private void RefreshItems(object sender, EventArgs e)
+		{
+			foreach (var item in this._viewModel.ItemGroups)
+			{
+				item.Clear();
+			}
+			this._viewModel.ItemGroups.Clear();
+
+			for (int i = 0; i < 30; i++)
+			{
+				_count++;
+				var g1 = new ModelIssue6761Group("Group " + _count);
+				_weakList.Add(new WeakReference<ModelIssue6761Group>(g1));
+				this._viewModel.ItemGroups.Add(g1);
+			}
+
+			CleanAndReport();
+		}
+
+		private void GCClick(object sender, EventArgs e)
+		{
+			CleanAndReport();
+		}
+		void CleanAndReport()
+		{ 
+			GC.Collect();
+			GC.WaitForPendingFinalizers();
+			GC.Collect();
+
+			CleanWeakList(_weakList);
+			_viewModel.DisposeString = $"{_weakList.Count} object(s) alive";
+
+			string report = $"MEMORY:{GC.GetTotalMemory(true)}";
+			_viewModel.TotalMemory = report;
+		}
+
+		private void CleanWeakList(IList<WeakReference<ModelIssue6761Group>> weakList)
+		{
+			ModelIssue6761Group item;
+			for (int i = weakList.Count-1; i >= 0; i--)
+			{
+				if (!weakList[i].TryGetTarget(out item))
+				{
+					weakList.RemoveAt(i);
+				}
+			}
+		}
+	}
+
+	[Preserve(AllMembers = true)]
+	public class ViewModelIssue6761 : INotifyPropertyChanged
+	{
+		public ObservableCollection<ModelIssue6761Group> ItemGroups { get; set; } = new ObservableCollection<ModelIssue6761Group>();
+		public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged;
+
+		private void NotifyPropertyChanged([CallerMemberName] string propertyName = null)
+		{
+			this.PropertyChanged?.Invoke(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName));
+		}
+
+
+		string _DisposeString;
+		public string DisposeString
+		{
+			get { return _DisposeString; } 
+			set
+			{
+				_DisposeString = value;
+				NotifyPropertyChanged();
+			}
+		}
+
+		string _totalMemory;
+		public string TotalMemory 
+		{
+			get => _totalMemory;
+			set
+			{
+				_totalMemory = value;
+				NotifyPropertyChanged();
+			}
+		}
+
+		public ViewModelIssue6761()
+		{
+
+		}
+	}
+
+	[Preserve(AllMembers = true)]
+	public class ModelIssue6761Group : ObservableCollection<ModelIssue6761>
+	{
+		public ModelIssue6761Group(string name)
+		{
+			GroupName = name;
+		}
+		public string GroupName { get; set; }
+
+	}
+
+	[Preserve(AllMembers = true)]
+	public class ModelIssue6761
+	{
+		public ModelIssue6761(string name)
+		{
+			Name = name;
+		}
+		public string Name { get; set; }
+
+	}
+}

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

@@ -53,6 +53,7 @@
       <DependentUpon>Issue11794.xaml</DependentUpon>
     </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue11769.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue6761.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12079.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12060.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12344.xaml.cs">
@@ -1668,6 +1669,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue11081.xaml.cs">
       <DependentUpon>Issue11081.xaml</DependentUpon>
     </Compile>
+    <Compile Update="$(MSBuildThisFileDirectory)Issue6761.xaml.cs">
+      <DependentUpon>Issue6761.xaml</DependentUpon>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue12372.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12374.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12222.cs" />
@@ -1823,6 +1827,9 @@
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue4040.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue6761.xaml">
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue8787.xaml" />
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue9771.xaml">
       <SubType>Designer</SubType>

Xamarin.Forms.Core/TemplatedItemsList.cs

@@ -231,17 +231,16 @@ public void Dispose()
 				return;
 
 			_itemsView.PropertyChanged -= BindableOnPropertyChanged;
+			ListProxy.CollectionChanged -= OnProxyCollectionChanged;
 
 			TItem header = HeaderContent;
-			if (header != null)
-				UnhookItem(header);
-
-			for (var i = 0; i < _templatedObjects.Count; i++)
+			if (header != null && header.BindingContext != null)
 			{
-				TItem item = _templatedObjects[i];
-				if (item != null)
-					UnhookItem(item);
+				UnhookItem(header);
 			}
+
+			HeaderContent = null;
+			UnhookAndClear();
 
 			_disposed = true;
 		}
@@ -710,7 +709,7 @@ void GroupedReset()
 				_groupedItems.Clear();
 			}
 
-			_templatedObjects.Clear();
+			UnhookAndClear();
 
 			var i = 0;
 			foreach (object item in ListProxy)
@@ -815,6 +814,7 @@ void OnCollectionChangedGrouped(NotifyCollectionChangedEventArgs e)
 						til.CollectionChanged -= OnInnerCollectionChanged;
 						oldItems.Add(til);
 						_groupedItems.RemoveAt(index);
+						UnhookItem(_templatedObjects[index]);
 						_templatedObjects.RemoveAt(index);
 						til.Dispose();
 					}
@@ -839,6 +839,7 @@ void OnCollectionChangedGrouped(NotifyCollectionChangedEventArgs e)
 						oldItems.Add(til);
 
 						_groupedItems.RemoveAt(index);
+						UnhookItem(_templatedObjects[index]);
 						_templatedObjects.RemoveAt(index);
 
 						newItems.Add(InsertGrouped(e.NewItems[i], index));

Xamarin.Forms.Platform.iOS/Cells/CellTableViewCell.cs

@@ -8,7 +8,7 @@ public class CellTableViewCell : UITableViewCell, INativeElementView
 	{
 		Cell _cell;
 
-		public Action<object, PropertyChangedEventArgs> PropertyChanged;
+		public event PropertyChangedEventHandler PropertyChanged;
 
 		bool _disposed;
 

Xamarin.Forms.Platform.iOS/Cells/TextCellRenderer.cs

@@ -26,7 +26,7 @@ public override UITableViewCell GetCell(Cell item, UITableViewCell reusableCell,
 			SetRealCell(item, tvc);
 
 			tvc.Cell = textCell;
-			tvc.PropertyChanged = HandleCellPropertyChanged;
+			tvc.PropertyChanged += HandleCellPropertyChanged;
 
 			tvc.TextLabel.Text = textCell.Text;
 			tvc.DetailTextLabel.Text = textCell.Detail;

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

@@ -1161,7 +1161,7 @@ public override UIView GetViewForHeader(UITableView tableView, nint section)
 				header.Cell = cell;
 
 				var renderer = (CellRenderer)Internals.Registrar.Registered.GetHandlerForObject<IRegisterable>(cell);
-				header.SetTableViewCell(renderer.GetCell(cell, null, tableView));
+				header.SetTableViewCell(renderer.GetCell(cell, header.GetTableViewCell(), tableView));
 
 				return header;
 			}
@@ -1173,8 +1173,13 @@ public override void HeaderViewDisplayingEnded(UITableView tableView, UIView hea
 
 				if (headerView is HeaderWrapperView wrapper)
 				{
-					wrapper.Cell?.SendDisappearing();
-					wrapper.Cell = null;
+					if (wrapper.Cell != null)
+					{
+						wrapper.Cell.SendDisappearing();
+						wrapper.SetTableViewCell(null);
+						wrapper.Cell.DisposeModalAndChildRenderers();
+						wrapper.Cell = null;
+					}
 				}
 			}
 
@@ -1514,10 +1519,18 @@ public HeaderWrapperView(string reuseIdentifier) : base((NSString)reuseIdentifie
 
 		public void SetTableViewCell(UITableViewCell value)
 		{
-			if (ReferenceEquals(_tableViewCell, value)) return;
+			if (ReferenceEquals(_tableViewCell, value)) 
+				return;
+
 			_tableViewCell?.RemoveFromSuperview();
 			_tableViewCell = value;
-			AddSubview(value);
+			if (value != null)
+				AddSubview(value);
+		}
+
+		public UITableViewCell GetTableViewCell()
+		{
+			return _tableViewCell;
 		}
 
 		public override void LayoutSubviews()