无法在初始设置后更改appbar标题可见性

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('My App'),
        ),
        body: HomeScreen(),
      ),
    );
  }
}

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  bool _isTitleVisible = true;

  void _toggleTitleVisibility() {
    setState(() {
      _isTitleVisible = !_isTitleVisible;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        IconButton(
          icon: Icon(Icons.toggle_on),
          onPressed: _toggleTitleVisibility,
        ),
        Expanded(
          child: Scaffold(
            appBar: AppBar(
              title: _isTitleVisible ? Text('My App') : null,
            ),
            body: Center(
              child: Text('Toggle the AppBar title visibility'),
            ),
          ),
        ),
      ],
    );
  }
}