如何使用CustomPainter绘制矩形画布视图

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('CustomPainter Demo')),
        body: Center(
          child: CustomPaint(
            size: Size(300, 300), // 设置画布大小
            painter: MyRectanglePainter(), // 使用自定义的 painter
          ),
        ),
      ),
    );
  }
}

class MyRectanglePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()
      ..color = Colors.blue // 设置矩形颜色
      ..style = PaintingStyle.fill; // 设置填充样式

    // 绘制矩形
    canvas.drawRect(Rect.fromLTWH(50, 50, 200, 200), paint);
  }

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