27.3 手势识别（缩放）

1.源代码

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  double imgWidth = 200.0;
  double imgHeight = 200.0;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: Scaffold(
          appBar: AppBar(title: Text("手势检测"),),
          body: Center(
              child: GestureDetector(
                child: Image.network("https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3669987090,2161151684&fm=26&gp=0.jpg", width: imgWidth,height: imgHeight,),
                onScaleUpdate: (ScaleUpdateDetails e) {
                  setState(() {
                    imgWidth= 200 * e.scale.clamp(0.8, 10.0);
                    imgHeight= 200 * e.scale.clamp(0.8, 10.0);
                  });
                },
              )
          ),
        )
    );
  }
}

2.解释源代码

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  //设置起始图片高宽度大小
  double imgWidth = 200.0;
  double imgHeight = 200.0;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: Scaffold(
          appBar: AppBar(title: Text("手势检测"),),
          body: Center(
              child: GestureDetector(
                child: Image.network("https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3669987090,2161151684&fm=26&gp=0.jpg", width: imgWidth,height: imgHeight,),
                onScaleUpdate: (ScaleUpdateDetails e) {
                  setState(() {
                    //缩放倍数在0.8到10倍之间
                    imgWidth= 200 * e.scale.clamp(0.8, 10.0);
                    imgHeight= 200 * e.scale.clamp(0.8, 10.0);
                  });
                },
              )
          ),
        )
    );
  }
}

3.效果图