feat(dragdrop): Initial D&D events support on ListView

src/Uno.UI/Generated/3.0.0.0/Windows.UI.Xaml.Controls/ListViewBase.cs

@@ -42,7 +42,7 @@ public  bool IsSwipeEnabled
 		// Skipping already declared property HeaderTemplate
 		// Skipping already declared property Header
 		// Skipping already declared property DataFetchSize
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
+		#if false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public  bool CanReorderItems
 		{
@@ -56,7 +56,7 @@ public  bool CanReorderItems
 			}
 		}
 		#endif
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
+		#if false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public  bool CanDragItems
 		{
@@ -195,15 +195,15 @@ public  bool IsActiveView
 			}
 		}
 		#endif
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
+		#if false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public static global::Windows.UI.Xaml.DependencyProperty CanDragItemsProperty { get; } = 
 		Windows.UI.Xaml.DependencyProperty.Register(
 			nameof(CanDragItems), typeof(bool), 
 			typeof(global::Windows.UI.Xaml.Controls.ListViewBase), 
 			new FrameworkPropertyMetadata(default(bool)));
 		#endif
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
+		#if false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public static global::Windows.UI.Xaml.DependencyProperty CanReorderItemsProperty { get; } = 
 		Windows.UI.Xaml.DependencyProperty.Register(
@@ -498,7 +498,7 @@ public  void CompleteViewChangeTo( global::Windows.UI.Xaml.Controls.SemanticZoom
 		// Forced skipping of method Windows.UI.Xaml.Controls.ListViewBase.HeaderProperty.get
 		// Forced skipping of method Windows.UI.Xaml.Controls.ListViewBase.HeaderTemplateProperty.get
 		// Forced skipping of method Windows.UI.Xaml.Controls.ListViewBase.HeaderTransitionsProperty.get
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
+		#if false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public  event global::Windows.UI.Xaml.Controls.DragItemsStartingEventHandler DragItemsStarting
 		{
@@ -563,7 +563,7 @@ public  void CompleteViewChangeTo( global::Windows.UI.Xaml.Controls.SemanticZoom
 			}
 		}
 		#endif
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
+		#if false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public  event global::Windows.Foundation.TypedEventHandler<global::Windows.UI.Xaml.Controls.ListViewBase, global::Windows.UI.Xaml.Controls.DragItemsCompletedEventArgs> DragItemsCompleted
 		{

src/Uno.UI/UI/Xaml/Controls/ItemsControl/ItemsControl.cs

@@ -949,6 +949,8 @@ protected virtual bool UpdateItems()
 
 		protected virtual void ClearContainerForItemOverride(DependencyObject element, object item) { }
 
+		internal virtual void ContainerClearedForItem(object item, SelectorItem itemContainer) { }
+
 		/// <summary>
 		/// Unset content of container. This should be called when the container is no longer going to be used.
 		/// </summary>
@@ -969,6 +971,7 @@ internal void CleanUpContainer(global::Windows.UI.Xaml.DependencyObject element)
 
 			}
 			ClearContainerForItemOverride(element, item);
+			ContainerClearedForItem(item, element as SelectorItem);
 
 			if (element is ContentPresenter presenter
 				&& (

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

@@ -25,6 +25,7 @@
 using Uno.Client;
 using System.Threading.Tasks;
 using System.Threading;
+using Windows.ApplicationModel.DataTransfer;
 using Windows.Foundation;
 using Uno.UI;
 
@@ -655,13 +656,88 @@ protected override void PrepareContainerForItemOverride(DependencyObject element
 			}
 		}
 
+		private const string DragItemsFormatId = DataPackage.UnoPrivateDataPrefix + "__dragged__items__";
+
 		internal override void ContainerPreparedForItem(object item, SelectorItem itemContainer, int itemIndex)
 		{
 			base.ContainerPreparedForItem(item, itemContainer, itemIndex);
 
+			if (CanDragItems)
+			{
+				itemContainer.CanDrag = true;
+				itemContainer.DragStarting += OnItemContainerDragStarting;
+				itemContainer.DropCompleted += OnItemContainerDragCompleted;
+			}
+
 			ContainerContentChanging?.Invoke(this, new ContainerContentChangingEventArgs(item, itemContainer, itemIndex));
 		}
 
+		internal override void ContainerClearedForItem(object item, SelectorItem itemContainer)
+		{
+			itemContainer.DragStarting -= OnItemContainerDragStarting;
+			itemContainer.DropCompleted -= OnItemContainerDragCompleted;
+
+			base.ContainerClearedForItem(item, itemContainer);
+		}
+
+		public event DragItemsStartingEventHandler DragItemsStarting;
+		public event TypedEventHandler<ListViewBase, DragItemsCompletedEventArgs> DragItemsCompleted;
+
+		public static DependencyProperty CanReorderItemsProperty { get; } = DependencyProperty.Register(
+			nameof(CanReorderItems),
+			typeof(bool),
+			typeof(ListViewBase),
+			new FrameworkPropertyMetadata(default(bool)));
+
+		public bool CanReorderItems
+		{
+			get => (bool)GetValue(CanReorderItemsProperty);
+			set => SetValue(CanReorderItemsProperty, value);
+		}
+
+		public static DependencyProperty CanDragItemsProperty { get; } = DependencyProperty.Register(
+			nameof(CanDragItems),
+			typeof(bool),
+			typeof(ListViewBase),
+			new FrameworkPropertyMetadata(default(bool)));
+
+		public bool CanDragItems
+		{
+			get => (bool)GetValue(CanDragItemsProperty);
+			set => SetValue(CanDragItemsProperty, value);
+		}
+
+		private static void OnItemContainerDragStarting(UIElement sender, DragStartingEventArgs innerArgs)
+		{
+			if (ItemsControlFromItemContainer(sender) is ListViewBase that && that.CanDragItems)
+			{
+				var items = that.SelectedItems.ToList();
+				if (that.ItemFromContainer(sender) is {} draggedItem && !items.Contains(draggedItem))
+				{
+					items.Add(draggedItem);
+				}
+				var args = new DragItemsStartingEventArgs(innerArgs, items);
+
+				that.DragItemsStarting?.Invoke(that, args);
+
+				// The application has the ability to add some items in the list, so make sure to freeze it only after event has been raised.
+				args.Data.SetData(DragItemsFormatId, args.Items.ToList());
+			}
+		}
+
+		private static void OnItemContainerDragCompleted(UIElement sender, DropCompletedEventArgs innerArgs)
+		{
+			// Note: It's not the responsibility of the ListView to remove item from the source, not matter the AcceptedOperation.
+
+			if (ItemsControlFromItemContainer(sender) is ListViewBase that && that.CanDragItems)
+			{
+				var items = innerArgs.Info.Data.FindRawData(DragItemsFormatId) as IReadOnlyList<object> ?? new List<object>(0);
+				var args = new DragItemsCompletedEventArgs(innerArgs, items);
+
+				that.DragItemsCompleted?.Invoke(that, args);
+			}
+		}
+
 		/// <summary>
 		/// Apply the multi-selection state to the provided item
 		/// </summary>

src/Uno.UI/UI/Xaml/DragDrop/DropCompletedEventArgs.cs

@@ -1,19 +1,27 @@
 #nullable enable
 
 using Windows.ApplicationModel.DataTransfer;
+using Windows.ApplicationModel.DataTransfer.DragDrop.Core;
 
 namespace Windows.UI.Xaml
 {
 	public partial class DropCompletedEventArgs : RoutedEventArgs
 	{
-		internal DropCompletedEventArgs(UIElement originalSource, DataPackageOperation result)
+		internal DropCompletedEventArgs(UIElement originalSource, CoreDragInfo info, DataPackageOperation result)
 			: base(originalSource)
 		{
+			Info = info;
 			DropResult = result;
 
 			CanBubbleNatively = false;
 		}
 
+		/// <summary>
+		/// Get access to the shared data, for internal usage only.
+		/// This has to be treated as readonly for drop completed.
+		/// </summary>
+		internal CoreDragInfo Info { get; }
+
 		public DataPackageOperation DropResult { get; }
 	}
 }

src/Uno.UI/UI/Xaml/UIElement.Pointers.cs

@@ -588,40 +588,35 @@ private Task<DataPackageOperation> StartDragAsyncCore(PointerPoint pointer, Poin
 				return Task.FromCanceled<DataPackageOperation>(CancellationToken.None);
 			}
 
+			var dragInfo = new CoreDragInfo(
+				source: ptArgs,
+				data: routedArgs.Data.GetView(),
+				routedArgs.AllowedOperations,
+				dragUI: routedArgs.DragUI);
+
 			if (!pointer.Properties.HasPressedButton)
 			{
 				// This is the UWP behavior: if no button is pressed, then the drag is completed immediately
-				var noneResult = Task.FromResult(DataPackageOperation.None);
-				OnDragCompleted(noneResult, this);
-				return noneResult;
+				OnDropCompleted(dragInfo, DataPackageOperation.None);
+				return Task.FromResult(DataPackageOperation.None);
 			}
 
-			var result = new TaskCompletionSource<DataPackageOperation>();
-			result.Task.ContinueWith(OnDragCompleted, this, TaskContinuationOptions.NotOnCanceled | TaskContinuationOptions.RunContinuationsAsynchronously);
+			var asyncResult = new TaskCompletionSource<DataPackageOperation>();
 
-			var dragInfo = new CoreDragInfo(
-				source: ptArgs,
-				data: routedArgs.Data.GetView(),
-				routedArgs.AllowedOperations,
-				dragUI: routedArgs.DragUI);
-			dragInfo.RegisterCompletedCallback(result.SetResult);
+			dragInfo.RegisterCompletedCallback(result =>
+			{
+				OnDropCompleted(dragInfo, result);
+				asyncResult.SetResult(result);
+			});
 
 			CoreDragDropManager.GetForCurrentView()!.DragStarted(dragInfo);
 
-			return result.Task;
+			return asyncResult.Task;
 		}
 
-		private static void OnDragCompleted(Task<DataPackageOperation> resultTask, object snd)
-		{
-			var that = (UIElement)snd;
-			var result = resultTask.IsFaulted
-				? DataPackageOperation.None
-				: resultTask.Result;
+		private void OnDropCompleted(CoreDragInfo info, DataPackageOperation result)
 			// Note: originalSource = this => DropCompleted is not actually a routed event, the original source is always the sender
-			var args = new DropCompletedEventArgs(that, result); 
-
-			that.SafeRaiseEvent(DropCompletedEvent, args);
-		}
+			=> SafeRaiseEvent(DropCompletedEvent, new DropCompletedEventArgs(this, info, result));
 
 		/// <summary>
 		/// Provides ability to a control to fulfill the data that is going to be shared, by drag-and-drop for instance.

src/Uno.UWP/ApplicationModel/DataTransfer/DataPackage.cs

@@ -18,6 +18,8 @@ namespace Windows.ApplicationModel.DataTransfer
 {
 	public partial class DataPackage
 	{
+		internal const string UnoPrivateDataPrefix = "__uno__private__data__";
+
 		public event TypedEventHandler<DataPackage, OperationCompletedEventArgs>? OperationCompleted;
 
 		private ImmutableDictionary<string, object> _data = ImmutableDictionary<string, object>.Empty;

src/Uno.UWP/ApplicationModel/DataTransfer/DataPackageView.cs

@@ -35,7 +35,7 @@ internal DataPackageView(
 
 		public DataPackageOperation RequestedOperation { get; }
 
-		public IReadOnlyList<string> AvailableFormats => _data.Keys.ToArray();
+		public IReadOnlyList<string> AvailableFormats => _data.Keys.Where(k => !k.StartsWith(DataPackage.UnoPrivateDataPrefix)).ToArray();
 
 		public IAsyncOperation<IReadOnlyDictionary<string, RandomAccessStreamReference>> GetResourceMapAsync()
 			=> Task.FromResult(_resourceMap as IReadOnlyDictionary<string, RandomAccessStreamReference>).AsAsyncOperation();
@@ -50,7 +50,11 @@ public bool Contains(string formatId)
 			return _data.ContainsKey(formatId);
 		}
 
+		internal object? FindRawData(string formatId)
+			=> _data.TryGetValue(formatId, out var data) ? data : null;
+
 		public IAsyncOperation<object> GetDataAsync(string formatId)
+			// Note: Using this, application can gain access to the data prefixed with DataPackage.UnoPrivateDataKey ... which is acceptable
 			=> GetData<object>(formatId);
 
 		public IAsyncOperation<Uri> GetWebLinkAsync()

src/Uno.UWP/ApplicationModel/DataTransfer/DragDrop/Core/CoreDragInfo.cs

@@ -13,9 +13,11 @@
 
 namespace Windows.ApplicationModel.DataTransfer.DragDrop.Core
 {
-	public partial class CoreDragInfo 
+	public partial class CoreDragInfo
 	{
-		private ImmutableList<Action<DataPackageOperation>>? _completions = ImmutableList<Action<DataPackageOperation>>.Empty;
+		internal delegate void Completed(DataPackageOperation result);
+
+		private ImmutableList<Completed>? _completions = ImmutableList<Completed>.Empty;
 		private int _result = -1;
 		private IDragEventSource _source;
 
@@ -65,7 +67,7 @@ internal void UpdateSource(IDragEventSource src)
 			(Position, Modifiers) = src.GetState();
 		}
 
-		internal void RegisterCompletedCallback(Action<DataPackageOperation> onCompleted)
+		internal void RegisterCompletedCallback(Completed onCompleted)
 		{
 			if (_result > 0
 				// If the Update return false, it means that the _completions is null, which means that the _result is now ready!
@@ -76,7 +78,7 @@ internal void RegisterCompletedCallback(Action<DataPackageOperation> onCompleted
 				onCompleted((DataPackageOperation)_result);
 			}
 
-			ImmutableList<Action<DataPackageOperation>>? AddCompletion(ImmutableList<Action<DataPackageOperation>>? completions, Action<DataPackageOperation> callback)
+			ImmutableList<Completed>? AddCompletion(ImmutableList<Completed>? completions, Completed callback)
 				=> completions?.Add(callback);
 		}