DragTarget example

main.dart

DragTarget(
  builder: (context, candidateData, rejectedData) {
    return Container(
      width: 200,
      height: 200,
      color: _acceptedColor,
    );
  },
  onWillAccept: (MaterialColor data) {
    debugPrint('onWillAccept()');
    return true;
  },
  onAccept: (MaterialColor data) {
    debugPrint('onAccept()');
    setState(() {
      _acceptedColor = data;
    });
  },
  onLeave: (MaterialColor data) {
    debugPrint('onLeave()');
    setState(() {
      _acceptedColor = Colors.grey;
    });
  },
),