1、Flutter把内容单独抽离成一个组件

//代码块 importM
import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(

      theme: ThemeData(  

        primarySwatch: Colors.yellow  //导航栏颜色  

      ),

      home: Scaffold(
          appBar: AppBar(title: const Text("这是导航栏", textDirection: TextDirection.rtl)),
          body:  const MyApp()
          ))
        );
}

//在Flutter中自定义组件其实就是一个类，这个类需要继承StatelessWidget/StatefulWidget
//代码块 statelessW
class MyApp extends StatelessWidget{
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return  const Center(
            child: Text(
              "你好flutter 我是一个自定义的主键",
              textDirection: TextDirection.ltr,
              style: TextStyle(
                  // color: Colors.red
                  color: Color.fromRGBO(190, 190, 34, 1),
                  fontSize: 40.0),
            ),
          );
  }
}