如何在 Flutter 中使用 CustomPainter 绘制圆环？

Question

我正在尝试使用 CustomPainter 类绘制一个半环，您可以在下图中看到它（浅紫色和浅橙色），但无法绘制它。 我只能画圆、方和线。

代码：

class MakeCircle extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint();
    paint.color = Colors.white12;
    var position = Offset(size.width /10, size.height / 10);
    canvas.drawCircle(position, 40.0, paint);
  }
  @override
  bool shouldRepaint(CustomPainter oldDelegate) => false;
}

这个只能画圆。

Answer 1

您必须为您的 Paint 对象使用 PaintingStyle.stroke 并使用 Path 类来绘制您的 arc

我为你创建了一个例子，请测试一下：

import 'dart:math' as math;

import 'package:flutter/material.dart';

main() {
  runApp(MaterialApp(
    home: Home(),
  ));
}

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: SizedBox(
          width: 300,
          height: 300,
          child: CustomPaint(
            painter: MakeCircle(strokeWidth: 50,strokeCap: StrokeCap.round),
          ),
        ),
      ),
    );
  }
}




class MakeCircle extends CustomPainter {
  final double strokeWidth;
  final StrokeCap strokeCap;

  MakeCircle({this.strokeCap = StrokeCap.square, this.strokeWidth = 10.0});

  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()
      ..color = Colors.blue
      ..strokeCap = StrokeCap.round
      ..strokeWidth = strokeWidth
      ..style = PaintingStyle.stroke; //important set stroke style

    final path = Path()
      ..moveTo(strokeWidth, strokeWidth)
      ..arcToPoint(Offset(size.width - strokeWidth, size.height - strokeWidth),
          radius: Radius.circular(math.max(size.width, size.height)));

    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => false;
}