如何使用firebase_auth和provider检测身份验证更改

import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:provider/provider.dart';

class AuthProvider with ChangeNotifier {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  User? _user;

  AuthProvider() {
    _auth.authStateChanges().listen((User? user) {
      _user = user;
      notifyListeners();
    });
  }

  User? get user => _user;

  Future<void> signInWithEmailAndPassword(String email, String password) async {
    try {
      await _auth.signInWithEmailAndPassword(email: email, password: password);
    } catch (e) {
      // 处理登录错误
    }
  }

  Future<void> signOut() async {
    await _auth.signOut();
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (_) => AuthProvider(),
      child: MaterialApp(
        home: Consumer<AuthProvider>(
          builder: (context, authProvider, _) {
            if (authProvider.user != null) {
              // 用户已登录
              return HomePage();
            } else {
              // 用户未登录
              return LoginPage();
            }
          },
        ),
      ),
    );
  }
}

class LoginPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Login'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text('Sign In'),
          onPressed: () {
            AuthProvider authProvider = Provider.of<AuthProvider>(context, listen: false);
            authProvider.signInWithEmailAndPassword('email', 'password');
          },
        ),
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text('Sign Out'),
          onPressed: () {
            AuthProvider authProvider = Provider.of<AuthProvider>(context, listen: false);
            authProvider.signOut();
          },
        ),
      ),
    );
  }
}

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