Null data in Draggable throws error when dragging on top of DragTarget #131542
Description
Is there an existing issue for this?
- I have searched the existing issues
- I have read the guide to filing a bug
Steps to reproduce
Currently, the data parameter in Draggable is nullable in nature. But this leads to Unexpected null value. error when a Draggable is dragged on top of a DragTarget when data == null since onAccept and onAcceptWithDetails are called as:
This also contradicts with onWillAccept since this allows data to be nullable while calling:
Expected results
The app should not throw an error even if data is null.
Actual results
The app throws Unexpected null value. error when Draggable is dragged on top of DragTarget.
Code sample
Code sample
import 'package:flutter/material.dart';
/// Flutter code sample for [Draggable].
void main() => runApp(const DraggableExampleApp());
class DraggableExampleApp extends StatelessWidget {
const DraggableExampleApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(title: const Text('Draggable Sample')),
body: const DraggableExample(),
),
);
}
}
class DraggableExample extends StatefulWidget {
const DraggableExample({super.key});
@override
State<DraggableExample> createState() => _DraggableExampleState();
}
class _DraggableExampleState extends State<DraggableExample> {
int acceptedData = 0;
@override
Widget build(BuildContext context) {
return Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
Draggable<int>(
// Uncomment to make it work.
// data: 10,
feedback: Container(
color: Colors.deepOrange,
height: 100,
width: 100,
child: const Icon(Icons.directions_run),
),
childWhenDragging: Container(
height: 100.0,
width: 100.0,
color: Colors.pinkAccent,
child: const Center(
child: Text('Child When Dragging'),
),
),
child: Container(
height: 100.0,
width: 100.0,
color: Colors.lightGreenAccent,
child: const Center(
child: Text('Draggable'),
),
),
),
DragTarget<int>(
builder: (
BuildContext context,
List<dynamic> accepted,
List<dynamic> rejected,
) {
return Container(
height: 100.0,
width: 100.0,
color: Colors.cyan,
child: Center(
child: Text('Value is updated to: $acceptedData'),
),
);
},
onAccept: (int? data) {
setState(() {
acceptedData += data ?? 1;
});
},
),
],
);
}
}
Screenshots or Video
Screenshots / Video demonstration
The app is stuck when the error occurs.
Logs
Logs
══╡ EXCEPTION CAUGHT BY GESTURE LIBRARY ╞═══════════════════════════════════════════════════════════
The following TypeErrorImpl was thrown while routing a pointer event:
Unexpected null value.
When the exception was thrown, this was the stack:
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 294:49 throw_
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 855:63 nullCheck
packages/flutter/src/widgets/drag_target.dart 720:38 didDrop
packages/flutter/src/widgets/drag_target.dart 885:7 finishDrag
packages/flutter/src/widgets/drag_target.dart 798:5 end
packages/flutter/src/gestures/multidrag.dart 156:13 [_up]
packages/flutter/src/gestures/multidrag.dart 258:12 [_handleEvent]
packages/flutter/src/gestures/pointer_router.dart 98:12 [_dispatch]
packages/flutter/src/gestures/pointer_router.dart 143:9 <fn>
dart-sdk/lib/_internal/js_dev_runtime/private/linked_hash_map.dart 21:13 forEach
packages/flutter/src/gestures/pointer_router.dart 141:17 [_dispatchEventToRoutes]
packages/flutter/src/gestures/pointer_router.dart 127:7 route
packages/flutter/src/gestures/binding.dart 488:19 handleEvent
packages/flutter/src/gestures/binding.dart 468:14 dispatchEvent
packages/flutter/src/rendering/binding.dart 439:11 dispatchEvent
packages/flutter/src/gestures/binding.dart 413:7 [_handlePointerEventImmediately]
packages/flutter/src/gestures/binding.dart 376:5 handlePointerEvent
packages/flutter/src/gestures/binding.dart 323:7 [_flushPointerEventQueue]
packages/flutter/src/gestures/binding.dart 292:9 [_handlePointerDataPacket]
lib/_engine/engine/platform_dispatcher.dart 1319:13 invoke1
lib/_engine/engine/platform_dispatcher.dart 303:5 invokeOnPointerDataPacket
lib/_engine/engine/pointer_binding.dart 168:39 [_onPointerData]
lib/_engine/engine/pointer_binding.dart 791:20 <fn>
lib/_engine/engine/pointer_binding.dart 720:14 <fn>
lib/_engine/engine/pointer_binding.dart 317:16 loggedHandler
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 574:37 _checkAndCall
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 579:39 dcall
router: Instance of 'PointerRouter'
route: Closure: (PointerEvent) => void from: function () { [native code] }
event: PointerUpEvent#64271(position: Offset(836.3, 154.2))
════════════════════════════════════════════════════════════════════════════════════════════════════Flutter Doctor output
Doctor output
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[✓] Connected device (2 available)
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! Doctor found issues in 1 category.