MaterialApp

MaterialApp 部件： 你可以理解为 layout

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('Welcome to Flutter'),
        ),
        body: HomeContent(),
      ),
      theme: ThemeData(
        primaryColor: Colors.pink,
      ),
    );
  }
}
class HomeContent extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.all(40),
      child: Text('测试组件'),
    );
  }
}