PositionedWidgetDraggableExample.dart

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const MyStatefulWidget(),
      ),
    );
  }
}


class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}


class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  double top = 0;
  double left = 0;

  @override
  Widget build(BuildContext context) {
    final child = Material(
      child: Container(
        height: 100.0,
        width: 100.0,
        color: Colors.red,
        child: const Center(
          child: Text('Draggable'),
        ),
      ),
    );
    return Stack(
      children: <Widget>[
        Positioned(
          top: top,
          left: left,
          child: Draggable<int>(
            data: 10,
            onDragUpdate: (details) {
              top = top + details.delta.dy;
              left = left + details.delta.dx;
              setState(() {});
            },
            child: child,
            feedback: child,
          ),
        ),
      ],
    );
  }
}