[译] 教你如何用 Flutter 的 GestureDetector 构建自定义滑块

import 'package:flutter/material.dart';
 
class CustomSliderThumbShape extends SliderThumbShape {
  // 绘制滑块
  Rect paint(PaintingContext context, Offset center, {Animation<double> activationAnimation, bool isDiscrete, TextPainter labelPainter, double value, double textScaleFactor}) {
    final canvas = context.canvas;
    final paint = Paint()..color = Colors.blue[400];
    final radius = 10.0; // 定义圆形滑块的半径
 
    canvas.drawCircle(center, radius, paint);
    return Rect.fromLTWH(center.dx - radius, center.dy - radius, 2 * radius, 2 * radius);
  }
}
 
class CustomSliderTrackShape extends SliderTrackShape {
  // 绘制轨道
  Rect paint(PaintingContext context, Offset offset, {RenderBox parentBox, SliderThemeData sliderTheme, Animation<double> valueIndicatorAnimation, TextDirection textDirection, double textScaleFactor, double trackHeight, bool isDiscrete}) {
    final canvas = context.canvas;
    final paint = Paint()..color = Colors.blueGrey[400];
    final rect = Rect.fromPoints(
      Offset(offset.dx, offset.dy + trackHeight / 2),
      Offset(offset.dx + parentBox.size.width, offset.dy + trackHeight / 2),
    );
 
    canvas.drawRect(rect, paint);
    return rect;
  }
}
 
class CustomSliderThumb extends StatefulWidget {
  @override
  _CustomSliderThumbState createState() => _CustomSliderThumbState();
}
 
class _CustomSliderThumbState extends State<CustomSliderThumb> {
  double _value = 0.0;
 
  void _updateValue(double value) {
    setState(() {
      _value = value;
    });
  }
 
  @override
  Widget build(BuildContext context) {
    return SliderTheme(
      data: SliderTheme.of(context).copyWith(
        thumbShape: CustomSliderThumbShape(),
        trackShape: CustomSliderTrackShape(),
      ),
      child: Slider(
        value: _value,
        onChanged: _updateValue,
      ),
    );
  }
}

这段代码定义了一个自定义滑块滑块形状CustomSliderThumbShape和自定义滑块轨道形状CustomSliderTrackShape，并在CustomSliderThumb这个StatefulWidget中使用了SliderTheme来应用这些自定义形状。滑块形状是一个圆形，轨道形状是一个灰色的矩形。滑块的位置通过Slider的value属性控制，并且在用户滑动滑块时，通过onChanged回调更新这个值。这个例子展示了如何使用SliderTheme来实现自定义滑块组件的样式。