fix(dragdrop): fire DragEnter and DragOver when firing DragStarting

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_UIElement.cs

@@ -32,8 +32,14 @@
 using Uno.UI;
 using Windows.UI;
 using Windows.ApplicationModel.Appointments;
+using Microsoft.UI.Input;
 using Microsoft.UI.Xaml.Hosting;
 using Uno.UI.Toolkit.Extensions;
+using KeyEventArgs = Windows.UI.Core.KeyEventArgs;
+
+#if !HAS_UNO_WINUI
+using Windows.UI.Input;
+#endif
 
 #if __IOS__
 using UIKit;
@@ -1758,7 +1764,7 @@ await UITestHelper.Load(new StackPanel
 			await TestServices.WindowHelper.WaitForIdle();
 
 			Assert.AreEqual(1, dragEnterCount);
-			Assert.AreEqual(1, dragOverCount);
+			Assert.AreEqual(2, dragOverCount);
 			Assert.AreEqual(0, dropCount);
 
 			mouse.Release();
@@ -1768,10 +1774,74 @@ await UITestHelper.Load(new StackPanel
 			}
 
 			Assert.AreEqual(1, dragEnterCount);
-			Assert.AreEqual(2, dragOverCount);
+			Assert.AreEqual(3, dragOverCount);
 			Assert.AreEqual(waitAfterRelease ? 1 : 0, dropCount);
 		}
 
+		[TestMethod]
+		[RunsOnUIThread]
+#if !HAS_INPUT_INJECTOR
+		[Ignore("InputInjector is not supported on this platform.")]
+#endif
+		public async Task When_DragEnter_Fires_Along_DragStarting()
+		{
+			if (TestServices.WindowHelper.IsXamlIsland)
+			{
+				Assert.Inconclusive("Drag and drop doesn't work in Uno islands.");
+			}
+
+			var injector = InputInjector.TryCreate() ?? throw new InvalidOperationException("Failed to init the InputInjector");
+			using var mouse = injector.GetMouse();
+
+			var rect = new Rectangle
+			{
+				Fill = new SolidColorBrush(Microsoft.UI.Colors.Red),
+				Width = 100,
+				Height = 100,
+				CanDrag = true
+			};
+
+			var border = new Border
+			{
+				Background = new SolidColorBrush(Microsoft.UI.Colors.Blue),
+				Padding = new Thickness(10),
+				Child = rect,
+				AllowDrop = true
+			};
+
+			var dragStartingCount = 0;
+			var dragEnterCount = 0;
+			var dragOverCount = 0;
+
+			border.DragEnter += (_, _) => dragEnterCount++;
+			border.DragOver += (_, _) => dragOverCount++;
+			rect.DragStarting += (_, _) => dragStartingCount++;
+
+			await UITestHelper.Load(border);
+
+			mouse.MoveTo(rect.GetAbsoluteBoundsRect().GetCenter());
+			await UITestHelper.WaitForIdle();
+			mouse.Press();
+			await UITestHelper.WaitForIdle();
+			mouse.MoveBy(GestureRecognizer.TapMaxXDelta / 3, 0);
+			await UITestHelper.WaitForIdle();
+			mouse.MoveBy(GestureRecognizer.TapMaxXDelta / 3, 0);
+			await UITestHelper.WaitForIdle();
+			mouse.MoveBy(GestureRecognizer.TapMaxXDelta / 3, 0);
+			await UITestHelper.WaitForIdle();
+
+			Assert.AreEqual(0, dragStartingCount);
+			Assert.AreEqual(0, dragEnterCount);
+			Assert.AreEqual(0, dragOverCount);
+
+			mouse.MoveBy(GestureRecognizer.TapMaxXDelta / 3, 0);
+			await UITestHelper.WaitForIdle();
+
+			Assert.AreEqual(1, dragStartingCount);
+			Assert.AreEqual(1, dragEnterCount);
+			Assert.AreEqual(1, dragOverCount);
+		}
+
 		#endregion
 #endif
 	}

src/Uno.UI/UI/Xaml/Input/PointerRoutedEventArgs.Android.cs

@@ -45,19 +45,26 @@ partial class PointerRoutedEventArgs
 		// then _lastNativeEvent.lastArgs and LastPointerEvent will diverge.
 		private static (MotionEvent nativeEvent, PointerRoutedEventArgs lastArgs)? _lastNativeEvent;
 
-		private readonly MotionEvent _nativeEvent;
 		private readonly int _pointerIndex;
+		private readonly ulong _timestamp;
+		private readonly float _x;
+		private readonly float _y;
 		private readonly UIElement _receiver;
 		private readonly PointerPointProperties _properties;
 
 		internal bool HasPressedButton => _properties.HasPressedButton;
 
 		internal PointerRoutedEventArgs(MotionEvent nativeEvent, int pointerIndex, UIElement originalSource, UIElement receiver) : this()
 		{
-			_nativeEvent = nativeEvent;
 			_pointerIndex = pointerIndex;
 			_receiver = receiver;
 
+			// NOTE: do not keep a reference to nativeEvent, which will be reused by android's native event bubbling and will be mutated as it
+			// goes up through the visual tree. Instead, get whatever values you need here and keep them in fields.
+			_timestamp = ToTimeStamp(nativeEvent.EventTime);
+			_x = nativeEvent.GetX(pointerIndex);
+			_y = nativeEvent.GetY(pointerIndex);
+
 			// Here we assume that usually pointerId is 'PointerIndexShift' bits long (8 bits / 255 ids),
 			// and that usually the deviceId is [0, something_not_too_big_hopefully_less_than_0x00ffffff].
 			// If deviceId is greater than 0x00ffffff, we might have a conflict but only in case of multi touch
@@ -73,7 +80,7 @@ internal PointerRoutedEventArgs(MotionEvent nativeEvent, int pointerIndex, UIEle
 			var isInContact = IsInContact(nativeEvent, basePointerType, nativePointerAction, nativePointerButtons);
 			var keys = nativeEvent.MetaState.ToVirtualKeyModifiers();
 
-			FrameId = (uint)_nativeEvent.EventTime;
+			FrameId = (uint)nativeEvent.EventTime;
 			Pointer = new Pointer(pointerId, basePointerType, isInContact, isInRange: true);
 			KeyModifiers = keys;
 			OriginalSource = originalSource;
@@ -101,38 +108,34 @@ internal PointerRoutedEventArgs(MotionEvent nativeEvent, int pointerIndex, UIEle
 				};
 			}
 
-			_properties = GetProperties(nativePointerType, nativePointerAction, nativePointerButtons); // Last: we need the Pointer property to be set!
+			_properties = GetProperties(nativeEvent, nativePointerType, nativePointerAction, nativePointerButtons); // Last: we need the Pointer property to be set!
 		}
 
 		public PointerPoint GetCurrentPoint(UIElement relativeTo)
 		{
-			var timestamp = ToTimeStamp(_nativeEvent.EventTime);
 			var device = global::Windows.Devices.Input.PointerDevice.For((global::Windows.Devices.Input.PointerDeviceType)Pointer.PointerDeviceType);
 			var (rawPosition, position) = GetPositions(relativeTo);
 
-			return new PointerPoint(FrameId, timestamp, device, Pointer.PointerId, rawPosition, position, Pointer.IsInContact, _properties);
+			return new PointerPoint(FrameId, _timestamp, device, Pointer.PointerId, rawPosition, position, Pointer.IsInContact, _properties);
 		}
 
 		private (Point raw, Point relative) GetPositions(UIElement relativeTo)
 		{
-			var phyX = _nativeEvent.GetX(_pointerIndex);
-			var phyY = _nativeEvent.GetY(_pointerIndex);
-
 			Point raw, relative;
 			if (relativeTo == null) // Relative to the window
 			{
 				var windowToReceiver = new int[2];
 				_receiver.GetLocationInWindow(windowToReceiver);
 
-				relative = new Point(phyX + windowToReceiver[0], phyY + windowToReceiver[1]).PhysicalToLogicalPixels();
+				relative = new Point(_x + windowToReceiver[0], _y + windowToReceiver[1]).PhysicalToLogicalPixels();
 			}
 			else if (relativeTo == _receiver) // Fast path
 			{
-				relative = new Point(phyX, phyY).PhysicalToLogicalPixels();
+				relative = new Point(_x, _y).PhysicalToLogicalPixels();
 			}
 			else
 			{
-				var posRelToReceiver = new Point(phyX, phyY).PhysicalToLogicalPixels();
+				var posRelToReceiver = new Point(_x, _y).PhysicalToLogicalPixels();
 				var posRelToTarget = UIElement.GetTransform(from: _receiver, to: relativeTo).Transform(posRelToReceiver);
 
 				relative = posRelToTarget;
@@ -148,13 +151,13 @@ public PointerPoint GetCurrentPoint(UIElement relativeTo)
 				var screenToReceiver = new int[2];
 				_receiver.GetLocationOnScreen(screenToReceiver);
 
-				raw = new Point(phyX + screenToReceiver[0], phyY + screenToReceiver[1]).PhysicalToLogicalPixels();
+				raw = new Point(_x + screenToReceiver[0], _y + screenToReceiver[1]).PhysicalToLogicalPixels();
 			}
 
 			return (raw, relative);
 		}
 
-		private PointerPointProperties GetProperties(MotionEventToolType type, MotionEventActions action, MotionEventButtonState buttons)
+		private PointerPointProperties GetProperties(MotionEvent nativeEvent, MotionEventToolType type, MotionEventActions action, MotionEventButtonState buttons)
 		{
 			var props = new PointerPointProperties
 			{
@@ -193,24 +196,24 @@ private PointerPointProperties GetProperties(MotionEventToolType type, MotionEve
 					//		 In that case we will still receive moves and up with the "StylusWithBarrel***" actions.
 					props.IsBarrelButtonPressed = buttons.HasFlag(MotionEventButtonState.StylusPrimary);
 					props.IsRightButtonPressed = Pointer.IsInContact;
-					props.Pressure = Math.Min(1f, _nativeEvent.GetPressure(_pointerIndex)); // Might exceed 1.0 on Android
+					props.Pressure = Math.Min(1f, nativeEvent.GetPressure(_pointerIndex)); // Might exceed 1.0 on Android
 					break;
 				case MotionEventToolType.Stylus:
 					props.IsBarrelButtonPressed = buttons.HasFlag(MotionEventButtonState.StylusPrimary);
 					props.IsLeftButtonPressed = Pointer.IsInContact;
-					props.Pressure = Math.Min(1f, _nativeEvent.GetPressure(_pointerIndex)); // Might exceed 1.0 on Android
+					props.Pressure = Math.Min(1f, nativeEvent.GetPressure(_pointerIndex)); // Might exceed 1.0 on Android
 					break;
 				case MotionEventToolType.Eraser:
 					props.IsEraser = true;
-					props.Pressure = Math.Min(1f, _nativeEvent.GetPressure(_pointerIndex)); // Might exceed 1.0 on Android
+					props.Pressure = Math.Min(1f, nativeEvent.GetPressure(_pointerIndex)); // Might exceed 1.0 on Android
 					break;
 
 				default:
 					break;
 			}
 
 			if (Android.OS.Build.VERSION.SdkInt >= BuildVersionCodes.M // ActionButton was introduced with API 23 (https://developer.android.com/reference/android/view/MotionEvent.html#getActionButton())
-				&& updates.TryGetValue(_nativeEvent.ActionButton, out var update))
+				&& updates.TryGetValue(nativeEvent.ActionButton, out var update))
 			{
 				props.PointerUpdateKind = update;
 			}

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

@@ -788,6 +788,8 @@ private async Task<DataPackageOperation> StartDragAsyncCore(PointerPoint pointer
 			});
 
 			XamlRoot.GetCoreDragDropManager(XamlRoot).DragStarted(dragInfo);
+			// Synchronously fire DragEnter+DragOver without waiting for another "mouse tick". This matches WinUI.
+			XamlRoot.VisualTree.ContentRoot.InputManager.DragDrop.ProcessMoved(ptArgs);
 
 			var result = await asyncResult.Task;