Flutter笔记：缩放手势

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(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('GestureDetector Example'),
        ),
        body: const Center(
          child: MyScale(),
        ),
      ),
    );
  }
}
class MyScale extends StatefulWidget {
  const MyScale({super.key});
  @override
  State<MyScale> createState() => _MyScaleState();
}
class _MyScaleState extends State<MyScale> {
  double _scale = 1.0;
  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onScaleStart: (ScaleStartDetails details) {
        print('缩放开始');
      },
      onScaleUpdate: (ScaleUpdateDetails details) {
        setState(() {
          _scale = details.scale;
        });
        print('缩放更新，当前缩放值：$_scale');
      },
      onScaleEnd: (ScaleEndDetails details) {
        print('缩放结束');
      },
      child: Transform.scale(
        scale: _scale,
        child: const FlutterLogo(size: 200),
      ),
    );
  }
}

const RawGestureDetector({
  Key? key,
  this.child,
  this.gestures = const <Type, GestureRecognizerFactory>{},
  this.behavior,
  this.excludeFromSemantics = false,
  this.semantics,
}) : super(key: key);

ScaleGestureRecognizer({
  Object? debugOwner, // 用于在调试打印中识别手势识别器的对象。
  PointerDeviceKind? kind, // 此手势识别器应该处理的设备类型
  this.dragStartBehavior = DragStartBehavior.start, // 确定在所有涉及此手势的计算中，用作起点的点
})

import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
void main() {
  runApp(const MyApp());
}
class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('GestureDetector Example'),
        ),
        body: const Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}
class MyWidget extends StatefulWidget {
  const MyWidget({Key? key}) : super(key: key);
  @override
  State<MyWidget> createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
  final _scaleRecognizer = ScaleGestureRecognizer();
  double _scale = 1.0;
  Offset _panOffset = Offset.zero;
  @override
  void initState() {
    super.initState();
    _scaleRecognizer
      ..onStart = _handleScaleStart
      ..onUpdate = _handleScaleUpdate
      ..onEnd = _handleScaleEnd;
  }
  @override
  void dispose() {
    _scaleRecognizer.dispose();
    super.dispose();
  }
  @override
  Widget build(BuildContext context) {
    return RawGestureDetector(
      gestures: {
        ScaleGestureRecognizer:
            GestureRecognizerFactoryWithHandlers<ScaleGestureRecognizer>(
          () => _scaleRecognizer,
          (ScaleGestureRecognizer instance) {},
        ),
      },
      child: Transform.scale(
        scale: _scale,
        child: Transform.translate(
          offset: _panOffset,
          child: const FlutterLogo(size: 200),
        ),
      ),
    );
  }
  void _handleScaleStart(ScaleStartDetails details) {
    print('缩放开始');
  }
  void _handleScaleUpdate(ScaleUpdateDetails details) {
    setState(() {
      _scale = details.scale;
      _panOffset = details.localFocalPoint;
    });
    print('缩放更新，当前缩放值：$_scale');
    print('拖动更新，当前偏移值：$_panOffset');
  }
  void _handleScaleEnd(ScaleEndDetails details) {
    print('缩放结束');
  }
}