flutter代码绘制屏幕下方的矩形底线-为什么(附加示例)

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('矩形底线示例'),
        ),
        body: Container(
          color: Colors.white,
          padding: EdgeInsets.all(20),
          child: Column(
            children: [
              Text(
                '这是一个示例文本',
                style: TextStyle(fontSize: 18),
              ),
              SizedBox(height: 10),
              Container(
                height: 1,
                width: double.infinity,
                color: Colors.black,
              ),
              SizedBox(height: 10),
              Text(
                '这是另一个示例文本',
                style: TextStyle(fontSize: 18),
              ),
            ],
          ),
        ),
      ),
    );
  }
}