Flutter GestureDetector：如何用两根手指捏/缩小或放大/缩小文本？

Question

我正在创建一个文本字段，例如Text或RichText。然后，我想使用捏放大/缩小文本的大小。现在，我尝试实现GestureDetector，但它也可以用一根手指放大/缩小。而且，目标锁定检测确实很困难。有时会冻结。捏定冻结后，我会添加视频，然后突然变大。第二个视频是这样的情况：仅当我用一根手指点击文本并移至左上角时，图像才会放大。理想的实现是检测捏和放大/缩小所有文本区域。当我只用一根手指时，请禁用缩放。您能给我一些提示，链接或代码如何解决或在哪里找到解决方案？

      body: GestureDetector(
          onScaleUpdate: (details) {
            setState(() {
              _textSize =
                  _initTextSize + (_initTextSize * (details.scale * .35));
            });
          },
          onScaleEnd: (ScaleEndDetails details) {
            setState(() {
              _initTextSize = _textSize;
            });
          },
          child: Center(
              child: SizedBox(
            height: _textSize,
            child: FittedBox(
              child: Text("Test"),
            ),
          ))),

Answer 1

在具有这些配置的Statefull小部件中

double _scaleFactor = 1.0;
double _baseScaleFactor = 1.0;

并且仅在更新时使用setState，使用scaleFactor的textScaleFactor属性上的RichText。

只有一个setState才能在开始缩放时重建小部件并存储初始因子

GestureDetector(
  onScaleStart: (details) {
    _baseScaleFactor = _scaleFactor;
  },
  onScaleUpdate: (details) {
    print(details.scale);
    setState(() {
      _scaleFactor = _baseScaleFactor * details.scale;
    });
  },
  child: Container(
    height: MediaQuery.of(context).size.height,
    width: MediaQuery.of(context).size.width,
    color: Colors.red,
    child: Center(
      child: Text(
        'Teste',
        textScaleFactor: _scaleFactor,
      ),
    ),
  ),
);

我放置的高度和宽度只是为了扩展和模拟手势检测器的区域。

Answer 2

解决方案：两指放大和缩小。

  import 'package:flutter/material.dart';
  import 'package:matrix_gesture_detector/matrix_gesture_detector.dart';

  class TransformText extends StatefulWidget {
    TransformText({Key key}) : super(key: key); // changed

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

  class _TransformTextState extends State<TransformText> {
    double scale = 0.0;

    @override
    Widget build(BuildContext context) {
      final ValueNotifier<Matrix4> notifier = ValueNotifier(Matrix4.identity());

      return Scaffold(
        appBar: AppBar(
          title: Text('Single finger Rotate text'), // changed
        ),
        body: Center(
          child: MatrixGestureDetector(
            onMatrixUpdate: (m, tm, sm, rm) {
              notifier.value = m;
            },
            child: AnimatedBuilder(
              animation: notifier,
              builder: (ctx, child) {
                return Transform(
                  transform: notifier.value,
                  child: Center(
                    child: Stack(
                      children: <Widget>[
                        Container(
                          color: Colors.red,
                          padding: EdgeInsets.all(10),
                          margin: EdgeInsets.only(top: 50),
                          child: Transform.scale(
                            scale:
                                1, // make this dynamic to change the scaling as in the basic demo
                            origin: Offset(0.0, 0.0),
                            child: Container(
                              height: 100,
                              child: Text(
                                "Two finger to zoom!!",
                                style:
                                    TextStyle(fontSize: 26, color: Colors.white),
                              ),
                            ),
                          ),
                        ),
                      ],
                    ),
                  ),
                );
              },
            ),
          ),
        ),
      );
    }
  }

Answer 3

完整代码。希望对您有所帮助。

import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final appTitle = 'Demo';

    return MaterialApp(
      title: appTitle,
      home: MyHomePage(title: appTitle),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(title),
        ),
        body: TransformText());
  }
}

class TransformText extends StatefulWidget {
  TransformText({Key key}) : super(key: key); // changed

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

class _TransformTextState extends State<TransformText> {
  double scale = 0.0;
  double _scaleFactor = 1.0;
  double _baseScaleFactor = 1.0;
  double _savedVal = 1.0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('GestureDetector Test'), // changed
      ),
      body: Column(
        children: <Widget>[
          RaisedButton(
              child: Text('get'),
              onPressed: () {
                _savedVal = _scaleFactor;
              }),
          RaisedButton(
              child: Text('set'),
              onPressed: () {
                setState(() {
                  _scaleFactor = _savedVal;
                });
              }),
          Expanded(
            child: Center(
                child: GestureDetector(
              behavior: HitTestBehavior.translucent,
              onScaleStart: (details) {
                _baseScaleFactor = _scaleFactor;
              },
              onScaleUpdate: (details) {
                setState(() {
                  _scaleFactor = _baseScaleFactor * details.scale;
                });
              },
              child: Container(
                height: MediaQuery.of(context).size.height,
                width: MediaQuery.of(context).size.width,
                child: Center(
                  child: Text(
                    'Test',
                    textScaleFactor: _scaleFactor,
                  ),
                ),
              ),
            )),
          ),
        ],
      ),
    );
  }
}