Make CollectionView SelectedItem and SelectedItems binding function correctly

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

@@ -0,0 +1,63 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.CollectionView)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.None, 47803, "CollectionView: Multi Selection Binding", PlatformAffected.All)]
+	public class CollectionViewBoundMultiSelection : TestNavigationPage
+	{
+		protected override void Init()
+		{
+#if APP
+			Device.SetFlags(new List<string>(Device.Flags ?? new List<string>()) { "CollectionView_Experimental" });
+
+			PushAsync(new GalleryPages.CollectionViewGalleries.SelectionGalleries.MultipleBoundSelection());
+#endif
+		}
+
+#if UITEST
+		[Test]
+		public void ItemsFromViewModelShouldBeSelected()
+		{
+			// Initially Items 1 and 2 should be selected (from the view model)
+			RunningApp.WaitForElement("Selected: Item 1, Item 2");
+
+			// Tapping Item 3 should select it and updating the binding
+			RunningApp.Tap("Item 3");	
+			RunningApp.WaitForElement("Selected: Item 1, Item 2, Item 3");
+
+			// Test clearing the selection from the view model and updating it
+			RunningApp.Tap("ClearAndAdd");	
+			RunningApp.WaitForElement("Selected: Item 1, Item 2");
+
+			// Test removing an item from the selection
+			RunningApp.Tap("Item 2");
+			RunningApp.WaitForElement("Selected: Item 1");
+
+			// Test setting a new selection list in the view mdoel 
+			RunningApp.Tap("Reset");	
+			RunningApp.WaitForElement("Selected: Item 1, Item 2");
+
+			RunningApp.Tap("Item 0");
+
+			// Test setting the selection directly with CollectionView.SelectedItems 
+			RunningApp.Tap("DirectUpdate");	
+			RunningApp.WaitForElement("Selected: Item 0, Item 3");
+		}
+#endif
+	}
+}

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

@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.CollectionView)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.None, 4539134, "CollectionView: Single Selection Binding", PlatformAffected.All)]
+	public class CollectionViewBoundSingleSelection : TestNavigationPage
+	{
+		protected override void Init()
+		{
+#if APP
+			Device.SetFlags(new List<string>(Device.Flags ?? new List<string>()) { "CollectionView_Experimental" });
+
+			PushAsync(new GalleryPages.CollectionViewGalleries.SelectionGalleries.SingleBoundSelection());
+#endif
+		}
+
+#if UITEST
+		[Test]
+		public void SelectionShouldUpdateBinding()
+		{
+			// Initially Item 2 should be selected (from the view model)
+			RunningApp.WaitForElement("Selected: Item: 2");
+
+			// Tapping Item 3 should select it and updating the binding
+			RunningApp.Tap("Item 3");	
+			RunningApp.WaitForElement("Selected: Item: 3");
+		}
+#endif
+	}
+}

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

@@ -11,6 +11,8 @@
   <ItemGroup>
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla59172.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue5766.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)CollectionViewBoundMultiSelection.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)CollectionViewBoundSingleSelection.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue4684.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue4992.xaml.cs">
       <DependentUpon>Issue4992.xaml</DependentUpon>

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/SelectionGalleries/BoundSelectionModel.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Collections.ObjectModel;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+using Xamarin.Forms.Internals;
+
+namespace Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries.SelectionGalleries
+{
+	[Preserve(AllMembers = true)]
+	internal class BoundSelectionModel : INotifyPropertyChanged
+	{
+		private CollectionViewGalleryTestItem _selectedItem;
+		private ObservableCollection<CollectionViewGalleryTestItem> _items;
+		private ObservableCollection<object> _selectedItems;
+
+		public event PropertyChangedEventHandler PropertyChanged;
+
+		public BoundSelectionModel()
+		{
+			Items = new ObservableCollection<CollectionViewGalleryTestItem>();
+
+			for (int n = 0; n < 4; n++)
+			{
+				Items.Add(new CollectionViewGalleryTestItem(DateTime.Now.AddDays(n), $"Item {n}", "coffee.png", n));
+			}
+
+			SelectedItem = Items[2];
+
+			SelectedItems = new ObservableCollection<object>()
+			{
+				Items[1], Items[2]
+			};
+		}
+
+		private void SelectedItemsCollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
+		{
+			OnPropertyChanged(nameof(SelectedItemsText));
+		}
+
+		void OnPropertyChanged([CallerMemberName] string propertyName = null)
+		{
+			PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+		}
+
+		public CollectionViewGalleryTestItem SelectedItem
+		{
+			get => _selectedItem;
+			set
+			{
+				_selectedItem = value;
+				OnPropertyChanged();
+			}
+		}
+
+		public ObservableCollection<object> SelectedItems
+		{
+			get => _selectedItems;
+			set
+			{
+				if (_selectedItems != null)
+				{
+					_selectedItems.CollectionChanged -= SelectedItemsCollectionChanged;
+				}
+
+				_selectedItems = value;
+
+				_selectedItems.CollectionChanged += SelectedItemsCollectionChanged;
+
+				OnPropertyChanged();
+				OnPropertyChanged(nameof(SelectedItemsText));
+			}
+		}
+
+		public ObservableCollection<CollectionViewGalleryTestItem> Items
+		{
+			get => _items;
+			set { _items = value; OnPropertyChanged(); }
+		}
+
+		public string SelectedItemsText => SelectedItems.ToCommaSeparatedList();
+	}
+}

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/SelectionGalleries/MultipleBoundSelection.xaml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries.SelectionGalleries.MultipleBoundSelection">
+    <ContentPage.Content>
+        <StackLayout Spacing="2">
+
+            <Label Text="The selected items in the CollectionView should always match the 'Selected' Label below. If it does not, this test has failed."
+                FontSize="10" VerticalOptions="CenterAndExpand" HorizontalOptions="CenterAndExpand" />
+
+            <Label Text="{Binding SelectedItemsText, StringFormat='{}Selected: {0}'}" FontAttributes="Bold"
+                FontSize="10" VerticalOptions="CenterAndExpand" HorizontalOptions="CenterAndExpand" />
+
+            <Button AutomationId="ClearAndAdd" HeightRequest="35" FontSize="10" Text="Clear VM selection and add Items 1 and 2" Clicked="ClearAndAdd" />
+
+            <Button AutomationId="Reset" HeightRequest="35" FontSize="10" Text="Set VM selection to new list" Clicked="ResetClicked" />
+
+            <Button AutomationId="DirectUpdate" HeightRequest="35" FontSize="10" Text="Clear CV selection and add Items 0 and 3" Clicked="DirectUpdateClicked" />
+
+            <CollectionView x:Name="CollectionView" ItemsSource="{Binding Items}" 
+                            SelectionMode="Multiple" SelectedItems="{Binding SelectedItems}">
+                <CollectionView.ItemTemplate>
+                    <DataTemplate>
+                        <StackLayout>
+                            <Image Source="{Binding Image}" HeightRequest="30" />
+                            <Label FontSize="10" Text="{Binding Caption}"></Label>
+                        </StackLayout>
+                    </DataTemplate>
+                </CollectionView.ItemTemplate>
+            </CollectionView>
+
+        </StackLayout>
+    </ContentPage.Content>
+</ContentPage>

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/SelectionGalleries/MultipleBoundSelection.xaml.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections.ObjectModel;
+using Xamarin.Forms.Xaml;
+
+namespace Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries.SelectionGalleries
+{
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	public partial class MultipleBoundSelection : ContentPage
+	{
+		BoundSelectionModel _vm;
+
+		public MultipleBoundSelection()
+		{
+			_vm = new BoundSelectionModel();
+			BindingContext = _vm;
+			InitializeComponent();
+		}
+
+		private void ClearAndAdd(object sender, EventArgs e)
+		{
+			_vm.SelectedItems.Clear();
+			_vm.SelectedItems.Add(_vm.Items[1]);
+			_vm.SelectedItems.Add(_vm.Items[2]);
+		}
+
+		private void ResetClicked(object sender, EventArgs e)
+		{
+			_vm.SelectedItems = new ObservableCollection<object>
+			{
+				_vm.Items[1],
+				_vm.Items[2]
+			};
+		}
+
+		private void DirectUpdateClicked(object sender, EventArgs e)
+		{
+			CollectionView.SelectedItems.Clear();
+			CollectionView.SelectedItems.Add(_vm.Items[0]);
+			CollectionView.SelectedItems.Add(_vm.Items[3]);
+		}
+	}
+}

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/SelectionGalleries/SelectionGallery.cs

@@ -22,6 +22,10 @@ public SelectionGallery()
 							new PreselectedItemGallery(), Navigation),
 						GalleryBuilder.NavButton("Preselected Items", () =>
 							new PreselectedItemsGallery(), Navigation),
+						GalleryBuilder.NavButton("Single Selection, Bound", () =>
+							new SingleBoundSelection(), Navigation),
+						GalleryBuilder.NavButton("Multiple Selection, Bound", () =>
+							new MultipleBoundSelection(), Navigation),
 					}
 				}
 			};

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/SelectionGalleries/SelectionHelpers.cs

@@ -0,0 +1,18 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries.SelectionGalleries
+{
+	internal static class SelectionHelpers
+	{
+		public static string ToCommaSeparatedList(this IEnumerable<object> items)
+		{
+			if (items == null)
+			{
+				return string.Empty;
+			}
+
+			return string.Join(", ", items.Cast<CollectionViewGalleryTestItem>().Select(i => i.Caption));
+		}
+	}
+}

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/SelectionGalleries/SelectionModeGallery.xaml.cs

@@ -35,8 +35,8 @@ void CollectionViewOnSelectionChanged(object sender, SelectionChangedEventArgs a
 
 		void UpdateSelectionInfo(IEnumerable<object> currentSelectedItems, IEnumerable<object> previousSelectedItems)
 		{
-			var previous = ToList(previousSelectedItems);
-			var current = ToList(currentSelectedItems);
+			var previous = previousSelectedItems.ToCommaSeparatedList();
+			var current = currentSelectedItems.ToCommaSeparatedList();
 
 			if (string.IsNullOrEmpty(previous))
 			{
@@ -58,7 +58,7 @@ void UpdateSelectionInfoCommand()
 
 			if(CollectionView.SelectionMode == SelectionMode.Multiple)
 			{
-				current = ToList(CollectionView?.SelectedItems);
+				current = CollectionView?.SelectedItems.ToCommaSeparatedList();
 			}
 			else if (CollectionView.SelectionMode == SelectionMode.Single)
 			{
@@ -67,16 +67,5 @@ void UpdateSelectionInfoCommand()
 
 			SelectedItemsCommand.Text = $"Selection (command): {current}";
 		}
-
-		static string ToList(IEnumerable<object> items)
-		{
-			if (items == null)
-			{
-				return string.Empty;
-			}
-
-			return items.Aggregate(string.Empty, 
-				(s, o) => s + (s.Length == 0 ? "" : ", ") + ((CollectionViewGalleryTestItem)o).Caption);
-		}
 	}
 }

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/SelectionGalleries/SingleBoundSelection.xaml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries.SelectionGalleries.SingleBoundSelection">
+    <ContentPage.Content>
+        <StackLayout Spacing="5">
+
+            <Label Text="The selected item in the CollectionView should match the 'Selected' Label below. If it does not, this test has failed."
+                VerticalOptions="CenterAndExpand" 
+                HorizontalOptions="CenterAndExpand" />
+
+            <Label Text="{Binding SelectedItem, StringFormat='{}Selected: {0}'}"
+                VerticalOptions="CenterAndExpand" 
+                HorizontalOptions="CenterAndExpand" />
+
+            <Button AutomationId="Reset" Text="Reset Selection to Item 0" Clicked="ResetClicked" />
+
+            <Button AutomationId="Clear" Text="Clear Selection" Clicked="ClearClicked" />
+
+            <CollectionView ItemsSource="{Binding Items}" SelectionMode="Single" SelectedItem="{Binding SelectedItem}">
+                <CollectionView.ItemTemplate>
+                    <DataTemplate>
+                        <StackLayout>
+                            <Image Source="{Binding Image}" HeightRequest="50" />
+                            <Label Text="{Binding Caption}"></Label>
+                        </StackLayout>
+                    </DataTemplate>
+                </CollectionView.ItemTemplate>
+            </CollectionView>
+
+        </StackLayout>
+    </ContentPage.Content>
+</ContentPage>