Declare DragTarget onMove event as taking a generic parameter (#76842)

packages/flutter/lib/src/widgets/drag_target.dart

@@ -59,12 +59,12 @@ typedef DragEndCallback = void Function(DraggableDetails details);
 /// Signature for when a [Draggable] leaves a [DragTarget].
 ///
 /// Used by [DragTarget.onLeave].
-typedef DragTargetLeave = void Function(Object? data);
+typedef DragTargetLeave<T> = void Function(T? data);
 
 /// Signature for when a [Draggable] moves within a [DragTarget].
 ///
 /// Used by [DragTarget.onMove].
-typedef DragTargetMove = void Function(DragTargetDetails<dynamic> details);
+typedef DragTargetMove<T> = void Function(DragTargetDetails<T> details);
 
 /// Where the [Draggable] should be anchored during a drag.
 enum DragAnchor {
@@ -653,12 +653,12 @@ class DragTarget<T extends Object> extends StatefulWidget {
 
   /// Called when a given piece of data being dragged over this target leaves
   /// the target.
-  final DragTargetLeave? onLeave;
+  final DragTargetLeave<T>? onLeave;
 
   /// Called when a [Draggable] moves within this [DragTarget].
   ///
   /// Note that this includes entering and leaving the target.
-  final DragTargetMove? onMove;
+  final DragTargetMove<T>? onMove;
 
   /// How to behave during hit testing.
   ///
@@ -712,7 +712,7 @@ class _DragTargetState<T extends Object> extends State<DragTarget<T>> {
       _rejectedAvatars.remove(avatar);
     });
     if (widget.onLeave != null)
-      widget.onLeave!(avatar.data);
+      widget.onLeave!(avatar.data as T?);
   }
 
   void didDrop(_DragAvatar<Object> avatar) {
@@ -732,7 +732,7 @@ class _DragTargetState<T extends Object> extends State<DragTarget<T>> {
     if (!mounted)
       return;
     if (widget.onMove != null)
-      widget.onMove!(DragTargetDetails<dynamic>(data: avatar.data, offset: avatar._lastOffset!));
+      widget.onMove!(DragTargetDetails<T>(data: avatar.data! as T, offset: avatar._lastOffset!));
   }
 
   @override

packages/flutter/test/widgets/draggable_test.dart

@@ -85,6 +85,83 @@ void main() {
     expect(moveCount, 1);
   });
 
+  // Regression test for https://github.com/flutter/flutter/issues/76825
+  testWidgets('Drag and drop - onLeave callback fires correctly with generic parameter',
+      (WidgetTester tester) async {
+    final Map<String,int> leftBehind = <String,int>{
+      'Target 1': 0,
+      'Target 2': 0,
+    };
+
+    await tester.pumpWidget(MaterialApp(
+      home: Column(
+        children: <Widget>[
+          const Draggable<int>(
+            data: 1,
+            child: Text('Source'),
+            feedback: Text('Dragging'),
+          ),
+          DragTarget<int>(
+            builder: (BuildContext context, List<int?> data, List<dynamic> rejects) {
+              return Container(height: 100.0, child: const Text('Target 1'));
+            },
+            onLeave: (int? data) {
+              if (data != null) {
+                leftBehind['Target 1'] = leftBehind['Target 1']! + data;
+              }
+            },
+          ),
+          DragTarget<int>(
+            builder: (BuildContext context, List<int?> data, List<dynamic> rejects) {
+              return Container(height: 100.0, child: const Text('Target 2'));
+            },
+            onLeave: (int? data) {
+              if (data != null) {
+                leftBehind['Target 2'] = leftBehind['Target 2']! + data;
+              }
+            },
+          ),
+        ],
+      ),
+    ));
+
+    expect(leftBehind['Target 1'], equals(0));
+    expect(leftBehind['Target 2'], equals(0));
+
+    final Offset firstLocation = tester.getCenter(find.text('Source'));
+    final TestGesture gesture = await tester.startGesture(firstLocation, pointer: 7);
+    await tester.pump();
+
+    expect(leftBehind['Target 1'], equals(0));
+    expect(leftBehind['Target 2'], equals(0));
+
+    final Offset secondLocation = tester.getCenter(find.text('Target 1'));
+    await gesture.moveTo(secondLocation);
+    await tester.pump();
+
+    expect(leftBehind['Target 1'], equals(0));
+    expect(leftBehind['Target 2'], equals(0));
+
+    final Offset thirdLocation = tester.getCenter(find.text('Target 2'));
+    await gesture.moveTo(thirdLocation);
+    await tester.pump();
+
+    expect(leftBehind['Target 1'], equals(1));
+    expect(leftBehind['Target 2'], equals(0));
+
+    await gesture.moveTo(secondLocation);
+    await tester.pump();
+
+    expect(leftBehind['Target 1'], equals(1));
+    expect(leftBehind['Target 2'], equals(1));
+
+    await gesture.up();
+    await tester.pump();
+
+    expect(leftBehind['Target 1'], equals(1));
+    expect(leftBehind['Target 2'], equals(1));
+  });
+
   testWidgets('Drag and drop - onLeave callback fires correctly', (WidgetTester tester) async {
     final Map<String,int> leftBehind = <String,int>{
       'Target 1': 0,
@@ -160,6 +237,81 @@ void main() {
     expect(leftBehind['Target 2'], equals(1));
   });
 
+  // Regression test for https://github.com/flutter/flutter/issues/76825
+  testWidgets('Drag and drop - onMove callback fires correctly with generic parameter',
+      (WidgetTester tester) async {
+    final Map<String,int> targetMoveCount = <String,int>{
+      'Target 1': 0,
+      'Target 2': 0,
+    };
+
+    await tester.pumpWidget(MaterialApp(
+      home: Column(
+        children: <Widget>[
+          const Draggable<int>(
+            data: 1,
+            child: Text('Source'),
+            feedback: Text('Dragging'),
+          ),
+          DragTarget<int>(
+            builder: (BuildContext context, List<int?> data, List<dynamic> rejects) {
+              return Container(height: 100.0, child: const Text('Target 1'));
+            },
+            onMove: (DragTargetDetails<int> details) {
+              targetMoveCount['Target 1'] =
+                  targetMoveCount['Target 1']! + details.data;
+            },
+          ),
+          DragTarget<int>(
+            builder: (BuildContext context, List<int?> data, List<dynamic> rejects) {
+              return Container(height: 100.0, child: const Text('Target 2'));
+            },
+            onMove: (DragTargetDetails<int> details) {
+              targetMoveCount['Target 2'] =
+                  targetMoveCount['Target 2']! + details.data;
+            },
+          ),
+        ],
+      ),
+    ));
+
+    expect(targetMoveCount['Target 1'], equals(0));
+    expect(targetMoveCount['Target 2'], equals(0));
+
+    final Offset firstLocation = tester.getCenter(find.text('Source'));
+    final TestGesture gesture = await tester.startGesture(firstLocation, pointer: 7);
+    await tester.pump();
+
+    expect(targetMoveCount['Target 1'], equals(0));
+    expect(targetMoveCount['Target 2'], equals(0));
+
+    final Offset secondLocation = tester.getCenter(find.text('Target 1'));
+    await gesture.moveTo(secondLocation);
+    await tester.pump();
+
+    expect(targetMoveCount['Target 1'], equals(1));
+    expect(targetMoveCount['Target 2'], equals(0));
+
+    final Offset thirdLocation = tester.getCenter(find.text('Target 2'));
+    await gesture.moveTo(thirdLocation);
+    await tester.pump();
+
+    expect(targetMoveCount['Target 1'], equals(1));
+    expect(targetMoveCount['Target 2'], equals(1));
+
+    await gesture.moveTo(secondLocation);
+    await tester.pump();
+
+    expect(targetMoveCount['Target 1'], equals(2));
+    expect(targetMoveCount['Target 2'], equals(1));
+
+    await gesture.up();
+    await tester.pump();
+
+    expect(targetMoveCount['Target 1'], equals(2));
+    expect(targetMoveCount['Target 2'], equals(1));
+  });
+
   testWidgets('Drag and drop - onMove callback fires correctly', (WidgetTester tester) async {
     final Map<String,int> targetMoveCount = <String,int>{
       'Target 1': 0,