Flutter：教你用CustomPaint画一个自定义的CircleProgressBar

import 'package:flutter/material.dart';
 
class CircleProgressBar extends CustomPainter {
  final double progress;
  final Color progressColor;
  final double strokeWidth;
 
  CircleProgressBar(this.progress, this.progressColor, this.strokeWidth);
 
  @override
  void paint(Canvas canvas, Size size) {
    final Paint paint = Paint()
      ..color = progressColor
      ..strokeWidth = strokeWidth
      ..strokeCap = StrokeCap.round
      ..style = PaintingStyle.stroke;
 
    final double progressAngle = 2 * math.pi * (progress / 100);
    final Rect rect = Offset.zero & size;
    final double radius = math.min(size.width / 2, size.height / 2);
 
    canvas.drawArc(rect.deflate(strokeWidth / 2), -math.pi / 2, progressAngle, false, paint);
  }
 
  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return true;
  }
}
 
class CircleProgressBarExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: SizedBox.fromSize(
          size: Size.square(100),
          child: CustomPaint(
            painter: CircleProgressBar(60, Colors.blue, 5),
          ),
        ),
      ),
    );
  }
}

这段代码定义了一个CircleProgressBar类，它继承自CustomPainter，用于绘制一个圆形进度条。在paint方法中，我们设置了绘制时用的Paint对象，并计算了进度对应的弧度。然后我们在提供的Canvas上绘制了一个弧形。在CircleProgressBarExample类中，我们创建了一个CustomPaint Widget，并将CircleProgressBar作为painter传入，以展示进度条的实际使用方法。