Flutter：使用 CustomClipper 绘制 N 角星

本文将向您展示如何使用Flutter 中的**CustomClipper类绘制n 角星**（5 角星、6 角星、10 角星、20 角星等）。无需安装任何第三方软件包。我们将从头开始制作东西。

重点是什么？

1.通过扩展CustomClipper类实现一个可重用的自定义裁剪器：

// This custom clipper help us achieve n-pointed star shape
class StarClipper extends CustomClipper {
  /// The number of points of the star
  final int points;
  StarClipper(this.points);

  // Degrees to radians conversion
  double _degreeToRadian(double deg) => deg * (math.pi / 180.0);

  @override
  Path getClip(Size size) {
    Path path = Path();
    double max = 2 * math.pi;

    double width = size.width;
    double halfWidth = width / 2;

    double wingRadius = halfWidth;
    double radius = halfWidth / 2;

    double degreesPerStep = _degreeToRadian(360 / points);
    double halfDegreesPerStep = degreesPerStep / 2;

    path.moveTo(width, halfWidth);

    for (double step = 0; step < max; step += degreesPerStep) {
      path.lineTo(halfWidth + wingRadius * math.cos(step),
          halfWidth + wingRadius * math.sin(step));
      path.lineTo(halfWidth + radius * math.cos(step + halfDegreesPerStep),
          halfWidth + radius * math.sin(step + halfDegreesPerStep));
    }

    path.close();
    return path;
  }

  // If the new instance represents different information than the old instance, this method will return true, otherwise it should return false.
  @override
  bool shouldReclip(CustomClipper oldClipper) {
    StarClipper starClipper = oldClipper as StarClipper;
    return points != starClipper.points;
  }
}

2. 现在您可以轻松绘制星星了，如下所示：

 SizedBox(
                height: 360,
                width: 360,
                child: ClipPath(
                  clipper: StarClipper(6),
                  child: Container(
                    height: 300,
                    color: Colors.amber,
                  ),
                ),
              ),

完整示例

预览

此示例生成 4 种不同的星形：5 角星、6 角星、10 角星和 20 角星。

编码

main.dart 中的完整源代码和解释：

// main.dart
import 'package:flutter/material.dart';
import 'dart:math' as math;

// This custom clipper help us achieve n-pointed star shape
class StarClipper extends CustomClipper {
  /// The number of points of the star
  final int points;
  StarClipper(this.points);

  // Degrees to radians conversion
  double _degreeToRadian(double deg) => deg * (math.pi / 180.0);

  @override
  Path getClip(Size size) {
    Path path = Path();
    double max = 2 * math.pi;

    double width = size.width;
    double halfWidth = width / 2;

    double wingRadius = halfWidth;
    double radius = halfWidth / 2;

    double degreesPerStep = _degreeToRadian(360 / points);
    double halfDegreesPerStep = degreesPerStep / 2;

    path.moveTo(width, halfWidth);

    for (double step = 0; step < max; step += degreesPerStep) {
      path.lineTo(halfWidth + wingRadius * math.cos(step),
          halfWidth + wingRadius * math.sin(step));
      path.lineTo(halfWidth + radius * math.cos(step + halfDegreesPerStep),
          halfWidth + radius * math.sin(step + halfDegreesPerStep));
    }

    path.close();
    return path;
  }

  // If the new instance represents different information than the old instance, this method will return true, otherwise it should return false.
  @override
  bool shouldReclip(CustomClipper oldClipper) {
    StarClipper starClipper = oldClipper as StarClipper;
    return points != starClipper.points;
  }
}

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'KindaCode.com',
      theme: ThemeData(
        primarySwatch: Colors.indigo,
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

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

class _MyHomePageState extends State {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Kindacode.com'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(20),
        child: Center(
          child: Column(
            children: [
              // 5-pointed star
              SizedBox(
                height: 180,
                width: 180,
                child: ClipPath(
                  clipper: StarClipper(5),
                  child: Container(
                    height: 150,
                    color: Colors.green,
                  ),
                ),
              ),

              // 6-pointed star
              SizedBox(
                height: 180,
                width: 180,
                child: ClipPath(
                  clipper: StarClipper(6),
                  child: Container(
                    height: 150,
                    color: Colors.amber,
                  ),
                ),
              ),

              // 10-pointed star
              SizedBox(
                height: 180,
                width: 180,
                child: ClipPath(
                  clipper: StarClipper(10),
                  child: Container(
                    height: 150,
                    color: Colors.indigo,
                  ),
                ),
              ),

              // 20-pointed star
              SizedBox(
                height: 180,
                width: 180,
                child: ClipPath(
                  clipper: StarClipper(20),
                  child: Container(
                    height: 150,
                    color: Colors.cyan,
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

结论

我们从头开始绘制自定义星形，没有使用任何第三个插件。如果您想在现代 Flutter 中探索更多新奇有趣的东西