flutter:在CustomPaint画布上放置常规小部件

import 'package:flutter/material.dart';

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

class CustomShapePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    // 绘制一个红色的矩形
    final paint = Paint()..color = Colors.red;
    canvas.drawRect(Rect.fromLTRB(0, 0, size.width, size.height), paint);

    // 绘制一个蓝色的圆形
    final bluePaint = Paint()..color = Colors.blue;
    canvas.drawCircle(Offset(size.width / 2, size.height / 2), 50, bluePaint);

    // 绘制文本
    final textPainter = TextPainter(
      text: TextSpan(
        text: 'Hello World',
        style: TextStyle(fontSize: 20, color: Colors.white),
      ),
      textDirection: TextDirection.ltr,
    );
    textPainter.layout();
    textPainter.paint(canvas, Offset(20, 20));
  }

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Custom Paint Example'),
        ),
        body: Center(
          child: Container(
            width: 200,
            height: 200,
            child: CustomPaint(
              painter: CustomShapePainter(),
            ),
          ),
        ),
      ),
    );
  }
}