Flutter :在屏幕上拖动窗口小部件(而不是拖放)

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Draggable Widget Example'),
        ),
        body: DraggableWidget(),
      ),
    );
  }
}

class DraggableWidget extends StatefulWidget {
  @override
  _DraggableWidgetState createState() => _DraggableWidgetState();
}

class _DraggableWidgetState extends State<DraggableWidget> {
  double xOffset = 0;
  double yOffset = 0;

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        Positioned(
          left: xOffset,
          top: yOffset,
          child: GestureDetector(
            onPanUpdate: (details) {
              setState(() {
                xOffset += details.delta.dx;
                yOffset += details.delta.dy;
              });
            },
            child: Container(
              width: 100,
              height: 100,
              color: Colors.blue,
              child: Center(
                child: Text(
                  'Drag me',
                  style: TextStyle(color: Colors.white),
                ),
              ),
            ),
          ),
        ),
      ],
    );
  }
}