从零开始绘制五星红旗，国庆日用Flutter构建的爱国画布

2023-11-01 04:53:17

在欢乐而隆重的国庆假期之际，让我们使用Flutter创建一个五星红旗，来庆祝这个伟大的节日。Flutter是一个开源的跨平台应用程序框架，可用于构建Android和iOS应用程序。

新建一个Flutter项目。

flutter create five_star_flag

在pubspec.yaml文件中添加必要的依赖项。

dependencies:
  flutter:
    sdk: flutter
  vector_math: ^2.1.0

创建一个新的Dart文件，并命名为five_star_flag.dart。
在five_star_flag.dart文件中添加以下代码。

import 'package:flutter/material.dart';
import 'package:vector_math/vector_math_64.dart';

class FiveStarFlag extends StatefulWidget {
  @override
  _FiveStarFlagState createState() => _FiveStarFlagState();
}

class _FiveStarFlagState extends State<FiveStarFlag> with SingleTickerProviderStateMixin {
  late AnimationController _controller;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(vsync: this, duration: Duration(seconds: 1));
    _controller.repeat(reverse: true);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return CustomPaint(
      painter: FiveStarFlagPainter(
        controller: _controller,
      ),
    );
  }
}

class FiveStarFlagPainter extends CustomPainter {
  final AnimationController controller;

  FiveStarFlagPainter({required this.controller});

  @override
  void paint(Canvas canvas, Size size) {
    // 绘制红色背景
    canvas.drawRect(Rect.fromLTWH(0, 0, size.width, size.height), Paint()..color = Colors.red);

    // 计算五角星的位置和大小
    double starWidth = size.width / 5;
    double starHeight = starWidth * sqrt(3) / 2;
    double starX = size.width / 2 - starWidth / 2;
    double starY = size.height / 2 - starHeight / 2;

    // 绘制五角星
    canvas.save();
    canvas.translate(starX, starY);
    canvas.rotate(controller.value * 2 * pi);
    canvas.scale(0.5);
    Path starPath = Path();
    starPath.moveTo(0, -starHeight / 2);
    starPath.lineTo(starWidth / 2, -starHeight / 4);
    starPath.lineTo(starWidth, 0);
    starPath.lineTo(starWidth / 2, starHeight / 4);
    starPath.lineTo(0, starHeight / 2);
    starPath.lineTo(-starWidth / 2, starHeight / 4);
    starPath.lineTo(-starWidth, 0);
    starPath.lineTo(-starWidth / 2, -starHeight / 4);
    starPath.close();
    canvas.drawPath(starPath, Paint()..color = Colors.yellow);
    canvas.restore();
  }

  @override
  bool shouldRepaint(FiveStarFlagPainter oldDelegate) => true;
}