如何在flutter中拖动控件的同时实现定位线条？

class MyDraggableWidget extends StatefulWidget {
  @override
  _MyDraggableWidgetState createState() => _MyDraggableWidgetState();
}

class _MyDraggableWidgetState extends State<MyDraggableWidget> {
  bool _isDragging = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Draggable Widget'),
      ),
      body: Column(
        children: [
          Draggable(
            child: Container(
              width: 100,
              height: 100,
              color: Colors.blue,
              child: Center(
                child: Text(
                  'Drag me',
                  style: TextStyle(color: Colors.white),
                ),
              ),
            ),
            feedback: Container(
              width: 100,
              height: 100,
              color: Colors.blue.withOpacity(0.5),
              child: Center(
                child: Text(
                  'Dragging',
                  style: TextStyle(color: Colors.white),
                ),
              ),
            ),
            onDragStarted: () {
              setState(() {
                _isDragging = true;
              });
            },
            onDragEnd: (details) {
              setState(() {
                _isDragging = false;
              });
            },
          ),
          SizedBox(height: 20),
          DragTarget(
            builder: (context, candidateData, rejectedData) {
              return Container(
                width: 200,
                height: 200,
                color: _isDragging ? Colors.green : Colors.grey,
                child: Center(
                  child: Text(
                    'Drop here',
                    style: TextStyle(color: Colors.white),
                  ),
                ),
              );
            },
            onWillAccept: (data) {
              return true;
            },
            onAccept: (data) {
              // 处理拖放完成后的逻辑
            },
          ),
        ],
      ),
    );
  }
}