From 15fc853ac8e6abd8bc9e07023e4deb679c452f1d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Javier=20Su=C3=A1rez?= <javiersuarezruiz@hotmail.com>
Date: Fri, 11 Dec 2020 12:54:52 +0100
Subject: [PATCH] [iOS] Cannot access a disposed object using CollectionView
 EmptyView (#12923) fixes #12910 fixes #12894

* Added repro sample

* Updated sample

* Updated repro sample

* Fix build error
---
 .../Issue12910.xaml                           | 105 ++++++++++++++
 .../Issue12910.xaml.cs                        | 134 ++++++++++++++++++
 ...rin.Forms.Controls.Issues.Shared.projitems |   4 +
 .../VisualElementRenderer.cs                  |   2 +-
 4 files changed, 244 insertions(+), 1 deletion(-)
 create mode 100644 Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12910.xaml
 create mode 100644 Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12910.xaml.cs

diff --git a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12910.xaml b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12910.xaml
new file mode 100644
index 00000000000..0b9e09f9f5c
--- /dev/null
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12910.xaml
@@ -0,0 +1,105 @@
+<?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"
+    x:Class="Xamarin.Forms.Controls.Issues.Issue12910"
+    xmlns:local="clr-namespace:Xamarin.Forms.Controls.Issues"  
+    Title="Issue 12910">
+    <ContentPage.Content>
+        <Grid
+            RowSpacing="0">
+            <Grid.RowDefinitions>
+                <RowDefinition Height="*" />
+                <RowDefinition Height="Auto" />
+            </Grid.RowDefinitions>
+            <Label
+                Padding="12"
+                BackgroundColor="Black"
+                TextColor="White"
+                Text="Pull to Refresh. Without exceptions, the test has passed."/>
+            <RefreshView
+                Grid.Row="1"
+				x:DataType="local:Issue12910ViewModel"
+				Command="{Binding LoadItemsCommand}"
+				IsRefreshing="{Binding IsBusy, Mode=TwoWay}">
+                <CollectionView
+                    x:Name="ItemsListView"
+                    ItemsSource="{Binding Items}"
+                    SelectionMode="None">
+                    <CollectionView.ItemsLayout>
+                        <GridItemsLayout
+							Orientation="Vertical"
+							HorizontalItemSpacing="10"
+							VerticalItemSpacing="10">
+                            <GridItemsLayout.Span>
+                                <OnIdiom
+								x:TypeArguments="x:Int32"
+								Default="2"
+								Tablet="4"
+								Desktop="6"/>
+                            </GridItemsLayout.Span>
+                        </GridItemsLayout>
+                    </CollectionView.ItemsLayout>
+                    <CollectionView.Header>
+                        <ScrollView
+						    Orientation="Horizontal"
+						    HorizontalScrollBarVisibility="Never">
+                            <StackLayout
+						        Orientation="Horizontal"
+						        Spacing="0"
+						        BindableLayout.ItemsSource="{Binding Items}">
+                                <BindableLayout.ItemTemplate>
+                                    <DataTemplate>
+                                        <Button
+										    Text="{Binding Text}"
+										    BackgroundColor="#555555"
+										    Command="{Binding Source={RelativeSource AncestorType={x:Type local:Issue12910ViewModel}}, Path=ItemTapped}"
+										    CommandParameter="{Binding .}"/>
+                                    </DataTemplate>
+                                </BindableLayout.ItemTemplate>
+                            </StackLayout>
+                        </ScrollView>
+                    </CollectionView.Header>
+                    <CollectionView.EmptyView>
+                        <StackLayout>
+                            <Label
+								HorizontalOptions="CenterAndExpand"
+								Text="Empty list"
+								VerticalOptions="EndAndExpand" />
+                            <Button
+								Command="{Binding LoadItemsCommand}"
+								HorizontalOptions="CenterAndExpand"
+								Text="Refresh"
+								VerticalOptions="StartAndExpand" />
+                        </StackLayout>
+                    </CollectionView.EmptyView>
+                    <CollectionView.ItemTemplate>
+                        <DataTemplate>
+                            <Frame
+							    CornerRadius="15" 
+					            Padding="15"
+							    x:DataType="model:Item">
+                                <StackLayout>
+                                    <Label
+									    Text="{Binding Text}" 
+									    LineBreakMode="TailTruncation" />
+                                    <Label
+									    Text="{Binding Description}" 
+									    LineBreakMode="TailTruncation" />
+                                </StackLayout>
+                                <Frame.GestureRecognizers>
+                                    <TapGestureRecognizer 
+									    NumberOfTapsRequired="1"
+									    Command="{Binding Source={RelativeSource AncestorType={x:Type local:Issue12910ViewModel}}, Path=ItemTapped}"		
+									    CommandParameter="{Binding .}">
+                                    </TapGestureRecognizer>
+                                </Frame.GestureRecognizers>
+                            </Frame>
+                        </DataTemplate>
+                    </CollectionView.ItemTemplate>
+                </CollectionView>
+            </RefreshView>
+        </Grid>
+    </ContentPage.Content>
+</controls:TestContentPage>
\ No newline at end of file
diff --git a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12910.xaml.cs b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12910.xaml.cs
new file mode 100644
index 00000000000..99b64cccd87
--- /dev/null
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12910.xaml.cs
@@ -0,0 +1,134 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using System;
+using System.Collections.ObjectModel;
+using System.Windows.Input;
+using System.Threading.Tasks;
+using System.Diagnostics;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+using Xamarin.Forms.Core.UITests;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.CollectionView)]
+#endif
+    [Preserve(AllMembers = true)]
+    [Issue(IssueTracker.Github, 12910,
+        "[Bug] 'Cannot access a disposed object. Object name: 'DefaultRenderer' - on ios with CollectionView and EmptyView",
+        PlatformAffected.iOS)]
+    public partial class Issue12910 : TestContentPage
+    {
+		readonly Issue12910ViewModel _viewModel;
+
+        public Issue12910()
+        {
+            _viewModel = new Issue12910ViewModel();
+#if APP
+            InitializeComponent();
+            BindingContext = _viewModel;
+#endif
+        }
+
+        protected override void Init()
+        {
+
+        }
+
+        protected override void OnAppearing()
+        {
+            base.OnAppearing();
+            _viewModel.OnAppearing();
+        }
+    }
+
+    public class Issue12910Model
+    {
+        public string Id { get; set; }
+        public string Text { get; set; }
+        public string Description { get; set; }
+    }
+
+    public class Issue12910ViewModel : BindableObject
+    {
+        bool _isBusy;
+        Issue12910Model _selectedItem;
+
+        public ObservableCollection<Issue12910Model> Items { get; }
+        public Command LoadItemsCommand { get; }
+        public Command AddItemCommand { get; }
+        public Command<Issue12910Model> ItemTapped { get; }
+
+        public Issue12910ViewModel()
+        {
+            Items = new ObservableCollection<Issue12910Model>();
+            LoadItemsCommand = new Command(async () => await ExecuteLoadItemsCommand());
+            ItemTapped = new Command<Issue12910Model>(OnItemSelected);
+            AddItemCommand = new Command(OnAddItem);
+        }
+
+        async Task ExecuteLoadItemsCommand()
+        {
+            IsBusy = true;
+
+            try
+            {
+                Items.Clear();
+
+                await Task.Delay(500);
+
+                Items.Add(new Issue12910Model { Id = "1", Text = "Text 1", Description = "Description 1" });
+                Items.Add(new Issue12910Model { Id = "2", Text = "Text 2", Description = "Description 2" });
+                Items.Add(new Issue12910Model { Id = "3", Text = "Text 3", Description = "Description 3" });
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine(ex);
+            }
+            finally
+            {
+                IsBusy = false;
+            }
+        }
+
+        public void OnAppearing()
+        {
+            IsBusy = true;
+            SelectedItem = null;
+        }
+
+        public bool IsBusy
+        {
+            get => _isBusy;
+            set
+            {
+                _isBusy = value;
+                OnPropertyChanged();
+            }
+        }
+
+        public Issue12910Model SelectedItem
+        {
+            get => _selectedItem;
+            set
+            {
+                _selectedItem = value;
+                OnPropertyChanged();
+            }
+        }
+
+        void OnAddItem(object obj)
+        {
+
+        }
+
+        void OnItemSelected(Issue12910Model item)
+        {
+
+        }
+    }
+}
\ 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 d85b773287c..39b4eff51fe 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
@@ -1653,6 +1653,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue12777.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue11911.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue11691.xaml.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue12910.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue8988.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12084.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12512.cs" />
@@ -2006,6 +2007,9 @@
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue11691.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue12910.xaml">
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue12084.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
diff --git a/Xamarin.Forms.Platform.iOS/VisualElementRenderer.cs b/Xamarin.Forms.Platform.iOS/VisualElementRenderer.cs
index c168c0e7e0b..f46911fb939 100644
--- a/Xamarin.Forms.Platform.iOS/VisualElementRenderer.cs
+++ b/Xamarin.Forms.Platform.iOS/VisualElementRenderer.cs
@@ -115,7 +115,7 @@ public override bool CanBecomeFirstResponder
 		{
 			get
 			{
-				if (Element.IsSet(PlatformConfiguration.iOSSpecific.VisualElement.CanBecomeFirstResponderProperty))
+				if (Element != null && Element.IsSet(PlatformConfiguration.iOSSpecific.VisualElement.CanBecomeFirstResponderProperty))
 					return PlatformConfiguration.iOSSpecific.VisualElement.GetCanBecomeFirstResponder(Element);
 
 				return base.CanBecomeFirstResponder;