draggable

main.dart

// Copyright 2019 the Dart project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final String title;

  const MyHomePage({
    super.key,
    required this.title,
  });

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  double getScale(BuildContext context) {
    final box = context.findRenderObject() as RenderBox?;
    if (box == null) {
      return 1.0;
    }
    final size =
        box.localToGlobal(Offset(1, 1)) - box.localToGlobal(Offset.zero);

    return size.dx;
  }

  double scale = 1.0;
  @override
  Widget build(BuildContext context) {
    double w = 100;
    double h = 100;

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: InteractiveViewer(
        child: Container(
            color: Colors.white,
            child: Builder(builder: (context) {
              return Stack(children: [
                Center(
                    child: Draggable(
                  dragAnchorStrategy: (draggable, context, position) {
                    scale = getScale(context);
                    final anchor =
                        childDragAnchorStrategy(draggable, context, position);
                    return anchor * scale;
                  },
                  childWhenDragging: Container(
                      width: w,
                      height: h,
                      color: Colors.red.withAlpha(100)), // boxDrag,
                  feedback: Builder(
                      builder: (context) => Container(
                          width: (w) * scale,
                          height: (h) * scale,
                          alignment: Alignment.center,
                          child: OverflowBox(
                              alignment: Alignment.center,
                              minWidth: 0,
                              minHeight: 0,
                              maxWidth: double.infinity,
                              maxHeight: double.infinity,
                              child: Transform.scale(
                                  scale: scale,
                                  child: Container(
                                      width: w,
                                      height: h,
                                      color: Colors.red))))),
                  child: Container(width: w, height: h, color: Colors.red),
                ))
              ]);
            })),
      ),
 
    );
  }
}