Flutter 使用 Canvas 绘制一个正方形

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});


  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: CustomPaint(
        painter: MyPainter(),
          size: const Size(600, 300),
      ),
    );
  }
}

class MyPainter extends CustomPainter{
  @override
  void paint(Canvas canvas, Size size) async{
    final paint = Paint()
      ..color = Colors.blue
      ..strokeWidth = 5
      ..style = PaintingStyle.stroke;

    final path = Path();
    path.moveTo(0, 0);
    path.lineTo(0, size.height);
    path.lineTo(size.width, size.height);
    path.lineTo(size.width, 0);
    path.lineTo(0, 0);
    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    return false;
  }
 
}