如何修改应用栏时刷新页面并显示更新后的应用栏？

在修改应用栏后，调用setState()方法更新状态并刷新页面。

代码示例：

import 'package:flutter/material.dart';

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  AppBar myAppBar = AppBar(
    title: Text('My App'),
  );

  void _changeAppBar() {
    setState(() {
      myAppBar = AppBar(
        title: Text('Updated Appbar'),
      );
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: myAppBar,
      body: Center(
        child: RaisedButton(
          onPressed: _changeAppBar,
          child: Text('Change AppBar'),
        ),
      ),
    );
  }
}