Add position data to `OnDragEnd` callback (#140378)

This PR adds localPosition/globalPosition data to the `DragEndDetails`
argument of the `onDragEnd` callback.

packages/flutter/lib/src/gestures/drag_details.dart

@@ -214,11 +214,14 @@ class DragEndDetails {
   DragEndDetails({
     this.velocity = Velocity.zero,
     this.primaryVelocity,
+    this.globalPosition = Offset.zero,
+    Offset? localPosition,
   }) : assert(
          primaryVelocity == null
            || (primaryVelocity == velocity.pixelsPerSecond.dx && velocity.pixelsPerSecond.dy == 0)
            || (primaryVelocity == velocity.pixelsPerSecond.dy && velocity.pixelsPerSecond.dx == 0),
-       );
+       ),
+      localPosition = localPosition ?? globalPosition;
 
   /// The velocity the pointer was moving when it stopped contacting the screen.
   ///
@@ -237,6 +240,23 @@ class DragEndDetails {
   /// Defaults to null if not specified in the constructor.
   final double? primaryVelocity;
 
+  /// The global position the pointer is located at when the drag
+  /// gesture has been completed.
+  ///
+  /// Defaults to the origin if not specified in the constructor.
+  ///
+  /// See also:
+  ///
+  ///  * [localPosition], which is the [globalPosition] transformed to the
+  ///    coordinate space of the event receiver.
+  final Offset globalPosition;
+
+  /// The local position in the coordinate system of the event receiver when
+  /// the drag gesture has been completed.
+  ///
+  /// Defaults to [globalPosition] if not specified in the constructor.
+  final Offset localPosition;
+
   @override
   String toString() => '${objectRuntimeType(this, 'DragEndDetails')}($velocity)';
 }

packages/flutter/lib/src/gestures/monodrag.dart

@@ -276,6 +276,7 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
   _DragState _state = _DragState.ready;
   late OffsetPair _initialPosition;
   late OffsetPair _pendingDragOffset;
+  late OffsetPair _finalPosition;
   Duration? _lastPendingEventTimestamp;
 
   /// When asserts are enabled, returns the last tracked pending event timestamp
@@ -351,6 +352,7 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
     if (_state == _DragState.ready) {
       _state = _DragState.possible;
       _initialPosition = OffsetPair(global: event.position, local: event.localPosition);
+      _finalPosition = _initialPosition;
       _pendingDragOffset = OffsetPair.zero;
       _globalDistanceMoved = 0.0;
       _lastPendingEventTimestamp = event.timeStamp;
@@ -418,6 +420,7 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
       final Offset localDelta = (event is PointerMoveEvent) ? event.localDelta : (event as PointerPanZoomUpdateEvent).localPanDelta;
       final Offset position = (event is PointerMoveEvent) ? event.position : (event.position + (event as PointerPanZoomUpdateEvent).pan);
       final Offset localPosition = (event is PointerMoveEvent) ? event.localPosition : (event.localPosition + (event as PointerPanZoomUpdateEvent).localPan);
+      _finalPosition = OffsetPair(local: localPosition, global: position);
       if (_state == _DragState.accepted) {
         _checkUpdate(
           sourceTimeStamp: event.timeStamp,
@@ -600,7 +603,11 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
         ? () => '$estimate; fling at ${details!.velocity}.'
         : () => '$estimate; judged to not be a fling.';
     }
-    details ??= DragEndDetails(primaryVelocity: 0.0);
+    details ??= DragEndDetails(
+      primaryVelocity: 0.0,
+      globalPosition: _finalPosition.global,
+      localPosition: _finalPosition.local,
+    );
 
     invokeCallback<void>('onEnd', () => onEnd!(details!), debugReport: debugReport);
   }
@@ -660,6 +667,8 @@ class VerticalDragGestureRecognizer extends DragGestureRecognizer {
     return DragEndDetails(
       velocity: Velocity(pixelsPerSecond: Offset(0, dy)),
       primaryVelocity: dy,
+      globalPosition: _finalPosition.global,
+      localPosition: _finalPosition.local,
     );
   }
 
@@ -715,6 +724,8 @@ class HorizontalDragGestureRecognizer extends DragGestureRecognizer {
     return DragEndDetails(
       velocity: Velocity(pixelsPerSecond: Offset(dx, 0)),
       primaryVelocity: dx,
+      globalPosition: _finalPosition.global,
+      localPosition: _finalPosition.local,
     );
   }
 
@@ -765,7 +776,11 @@ class PanGestureRecognizer extends DragGestureRecognizer {
     }
     final Velocity velocity = Velocity(pixelsPerSecond: estimate.pixelsPerSecond)
         .clampMagnitude(minFlingVelocity ?? kMinFlingVelocity, maxFlingVelocity ?? kMaxFlingVelocity);
-    return DragEndDetails(velocity: velocity);
+    return DragEndDetails(
+      velocity: velocity,
+      globalPosition: _finalPosition.global,
+      localPosition: _finalPosition.local,
+    );
   }
 
   @override

packages/flutter/test/widgets/gesture_detector_test.dart

@@ -125,6 +125,40 @@ void main() {
     expect(didEndPan, isTrue);
   });
 
+  testWidgets('DragEndDetails returns the last known position', (WidgetTester tester) async {
+    Offset updateOffset = const Offset(10.0, 10.0);
+    const EdgeInsets paddingOffset = EdgeInsets.all(10.0);
+    Offset? endOffset;
+    Offset? globalEndOffset;
+
+    await tester.pumpWidget(
+      Padding(
+        padding: paddingOffset,
+        child: GestureDetector(
+          onPanStart: (DragStartDetails details) {
+          },
+          onPanUpdate: (DragUpdateDetails details) {
+            updateOffset += details.delta;
+          },
+          onPanEnd: (DragEndDetails details) {
+            endOffset = details.localPosition;
+            globalEndOffset = details.globalPosition;
+          },
+          child: Container(
+            color: const Color(0xFF00FF00),
+          ),
+        ),
+      ),
+    );
+
+    await tester.dragFrom(const Offset(20.0, 20.0), const Offset(30.0, 40.0));
+
+    expect(endOffset, isNotNull);
+    expect(updateOffset, endOffset);
+    // Make sure details.globalPosition works correctly.
+    expect(Offset(endOffset!.dx + paddingOffset.left, endOffset!.dy + paddingOffset.top), globalEndOffset);
+  });
+
   group('Tap', () {
     final ButtonVariant buttonVariant = ButtonVariant(
       values: <int>[kPrimaryButton, kSecondaryButton, kTertiaryButton],