使用自定义笔画帽在 flutter 中创建自定义圆形进度指示器

Question

我需要创建这个百分比指标

我怎样才能做到这一点？我尝试过 Flutter 中的%_indicator 包，但主要问题是我们的StrokeCap 选项数量有限。我也尝试过用两条弧线来做到这一点，但问题仍然存在。有没有一种方法可以创建自定义中风帽，或者可能有另一种没有canvas.drawArc的方法？

Answer 1

您可以使用 CustomPainter 来实现此目的。以下是我的解决方案。

注意 您可以传入动态值来更新进度条的值。我还没有这样做，因为一旦渲染正确，实现起来应该很简单;)。您还可以更新颜色以满足您的需要！

import 'package:flutter/material.dart';
import 'package:vector_math/vector_math.dart' as vmath;

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: TestPage(),
    );
  }
}

class TestPage extends StatelessWidget {
  const TestPage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Container(
          width: 200,
          height: 200,
          child: CustomPaint(
            painter: MyPainter(),
            child: Container(),
          ),
        ),
      ),
    );
  }
}

class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    // Get the center of the canvas 
    final center = Offset(size.width / 2, size.height / 2);
    
    // Draw the gray background seen on the progress indicator
    // This will act as the background layer.
    canvas.drawCircle(
      center,
      85,
      Paint()
        ..style = PaintingStyle.stroke
        ..color = Colors.black12
        ..strokeWidth = 30,
    );

    // Create a new layer where we will be painting the 
    // actual progress indicator
    canvas.saveLayer(
      Rect.fromCenter(center: center, width: 200, height: 200),
      Paint(),
    );

    // Draw the light green portion of the progress indicator
    canvas.drawArc(
      Rect.fromCenter(center: center, width: 170, height: 170),
      vmath.radians(0),
      vmath.radians(200),
      false,
      Paint()
        ..style = PaintingStyle.stroke
        ..strokeCap = StrokeCap.round
        ..color = Colors.green[100]
        ..strokeWidth = 30,
    );

    // Draw the dark green portion of the progress indicator
    // Basically, this covers the entire progress indicator circle.
    // But because we have set the blending mode to srouce-in (BlendMode.srcIn), 
    // only the segment that is overlapping with the lighter portion will be visible.
    canvas.drawArc(
      Rect.fromCenter(center: center, width: 155, height: 155),
      vmath.radians(0),
      vmath.radians(360),
      false,
      Paint()
        ..style = PaintingStyle.stroke
        ..strokeCap = StrokeCap.round
        ..color = Colors.green
        ..strokeWidth = 15
        ..blendMode = BlendMode.srcIn,
    );
    // we fatten the layer
    canvas.restore();
  }

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

您应该得到如下所示的输出：