Merge pull request #12666 from AvaloniaUI/gesture_cancel

Call CaptureLost on gestures when pointer loses capture

src/Avalonia.Base/Input/GestureRecognizers/GestureRecognizerCollection.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using Avalonia.Controls;
@@ -59,6 +60,20 @@ namespace Avalonia.Input.GestureRecognizers
             return e.Handled;
         }
 
+        internal void HandleCaptureLost(IPointer pointer)
+        {
+            if (_recognizers == null || pointer is not Pointer p)
+                return;
+
+            foreach (var r in _recognizers)
+            {
+                if (p.CapturedGestureRecognizer == r)
+                    continue;
+
+                r.PointerCaptureLostInternal(pointer);
+            }
+        }
+
         internal bool HandlePointerReleased(PointerReleasedEventArgs e)
         {
             if (_recognizers == null)

src/Avalonia.Base/Input/GestureRecognizers/PinchGestureRecognizer.cs

@@ -1,4 +1,5 @@
-using Avalonia.Input.GestureRecognizers;
+using System.Diagnostics;
+using Avalonia.Input.GestureRecognizers;
 
 namespace Avalonia.Input
 {
@@ -110,6 +111,7 @@ namespace Avalonia.Input
 
                     _secondContact = null;
                 }
+
                 Target?.RaiseEvent(new PinchEndedEventArgs());
             }
         }

src/Avalonia.Base/Input/InputElement.cs

@@ -230,6 +230,7 @@ namespace Avalonia.Input
             PointerMovedEvent.AddClassHandler<InputElement>((x, e) => x.OnGesturePointerMoved(e), handledEventsToo: true);
             PointerPressedEvent.AddClassHandler<InputElement>((x, e) => x.OnGesturePointerPressed(e), handledEventsToo: true);
             PointerReleasedEvent.AddClassHandler<InputElement>((x, e) => x.OnGesturePointerReleased(e), handledEventsToo: true);
+            PointerCaptureLostEvent.AddClassHandler<InputElement>((x, e) => x.OnGesturePointerCaptureLost(e), handledEventsToo: true);
         }
 
         public InputElement()
@@ -615,6 +616,11 @@ namespace Avalonia.Input
                 }
         }
 
+        private void OnGesturePointerCaptureLost(PointerCaptureLostEventArgs e)
+        {
+            _gestureRecognizers?.HandleCaptureLost(e.Pointer);
+        }
+
         private void OnGesturePointerPressed(PointerPressedEventArgs e)
         {
             if (!e.IsGestureRecognitionSkipped)

src/Avalonia.Base/Input/Pointer.cs

@@ -91,12 +91,16 @@ namespace Avalonia.Input
         internal void CaptureGestureRecognizer(GestureRecognizer? gestureRecognizer)
         {
             if (CapturedGestureRecognizer != gestureRecognizer)
+            {
                 CapturedGestureRecognizer?.PointerCaptureLostInternal(this);
+            }
+
+            CapturedGestureRecognizer = gestureRecognizer;
 
             if (gestureRecognizer != null)
+            {
                 Capture(null);
-
-            CapturedGestureRecognizer = gestureRecognizer;
+            }
         }
     }
 }

tests/Avalonia.Base.UnitTests/Input/GesturesTests.cs

@@ -487,6 +487,40 @@ namespace Avalonia.Base.UnitTests.Input
             Assert.True(raised);
         }
 
+        [Fact]
+        public void Gestures_Should_Be_Cancelled_When_Pointer_Capture_Is_Lost()
+        {
+            Border border = new Border()
+            {
+                Width = 100,
+                Height = 100,
+                Background = new SolidColorBrush(Colors.Red)
+            };
+            border.GestureRecognizers.Add(new PinchGestureRecognizer());
+            var root = new TestRoot
+            {
+                Child = border
+            };
+            var raised = false;
+
+            root.AddHandler(Gestures.PinchEvent, (_, _) => raised = true);
+
+            var firstPoint = new Point(5, 5);
+            var secondPoint = new Point(10, 10);
+
+            var firstTouch = new TouchTestHelper();
+            var secondTouch = new TouchTestHelper();
+
+            firstTouch.Down(border, position: firstPoint);
+
+            firstTouch.Cancel();
+
+            secondTouch.Down(border, position: secondPoint);
+            secondTouch.Move(border, position: new Point(20, 20));
+
+            Assert.False(raised);
+        }
+
         [Fact]
         public void Scrolling_Should_Start_After_Start_Distance_Is_Exceeded()
         {

tests/Avalonia.UnitTests/TouchTestHelper.cs

@@ -61,5 +61,11 @@ namespace Avalonia.UnitTests
             Down(target, source, position, modifiers);
             Up(target, source, position, modifiers);
         }
+
+        public void Cancel()
+        {
+            _pointer.Capture(null);
+            _pointer.CaptureGestureRecognizer(null);
+        }
     }
 }