flutter使用GestureDetector监听页面缩放了

可以使用ScaleGestureDetector来监听手势缩放操作。下面是一个简单的示例：

import 'package:flutter/material.dart';

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

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

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  double _scale = 1.0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: GestureDetector(
          onScaleUpdate: (ScaleUpdateDetails details) {
            setState(() {
              _scale = details.scale;
            });
          },
          child: Transform.scale(
            scale: _scale,
            child: Container(
              width: 200,
              height: 200,
              color: Colors.blue,
              child: Center(
                child: Text(
                  'Scale: ${_scale.toStringAsFixed(2)}',
                  style: TextStyle(fontSize: 20),
                ),
              ),
            ),
          ),
        ),
      ),
    );
  }
}

在上面的示例中，我们使用GestureDetector来监听手势缩放操作，并且使用Transform.scale来对Container进行缩放。onScaleUpdate回调函数会在缩放过程中被调用，我们可以在其中更新状态并重新构建UI来更新缩放效果。