如何在flutter中添加登机画面？

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Login Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: LoginPage(),
    );
  }
}

class LoginPage extends StatefulWidget {
  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  String username = '';
  String password = '';

  void login() {
    // 处理登陆逻辑
    if (username == 'admin' && password == 'password') {
      // 登陆成功，跳转到主页面
      Navigator.pushReplacement(
        context,
        MaterialPageRoute(builder: (context) => HomePage()),
      );
    } else {
      // 登陆失败，显示错误提示
      showDialog(
        context: context,
        builder: (context) => AlertDialog(
          title: Text('登陆失败'),
          content: Text('用户名或密码错误'),
          actions: [
            TextButton(
              child: Text('确定'),
              onPressed: () => Navigator.pop(context),
            ),
          ],
        ),
      );
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('登陆'),
      ),
      body: Padding(
        padding: EdgeInsets.all(16.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            TextField(
              onChanged: (value) => setState(() => username = value),
              decoration: InputDecoration(
                labelText: '用户名',
              ),
            ),
            SizedBox(height: 16.0),
            TextField(
              onChanged: (value) => setState(() => password = value),
              obscureText: true,
              decoration: InputDecoration(
                labelText: '密码',
              ),
            ),
            SizedBox(height: 16.0),
            ElevatedButton(
              onPressed: login,
              child: Text('登陆'),
            ),
          ],
        ),
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('主页'),
      ),
      body: Center(
        child: Text('欢迎登陆！'),
      ),
    );
  }
}