Dart 如何在 Flutter 中管理 Firebase 身份验证状态

Null safe code (using provider)

Full code:

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  runApp(
    ChangeNotifierProvider<AuthModel>(
      create: (_) => AuthModel(),
      child: MaterialApp(
        home: Consumer<AuthModel>(
          builder: (_, auth, __) => auth.isSignedIn ? HomePage() : WelcomePage(),
        ),
      ),
    ),
  );
}

class WelcomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('WelcomePage')),
      body: Center(
        child: ElevatedButton(
          onPressed: () => Navigator.push(context, MaterialPageRoute(builder: (_) => LoginPage())),
          child: Text('Go to Login Page'),
        ),
      ),
    );
  }
}

class LoginPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Login Page')),
      body: Center(
        child: ElevatedButton(
          onPressed: () async {
            final model = context.read<AuthModel>();
            await model.signIn(email: 'test@test.com', password: 'test1234');
            Navigator.pop(context);
          },
          child: Text('Login'),
        ),
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('HomePage')),
      body: Center(
        child: FloatingActionButton.extended(
          onPressed: () async {
            final model = context.read<AuthModel>();
            await model.signOut();
          },
          label: Text('Log out'),
        ),
      ),
    );
  }
}

class AuthModel extends ChangeNotifier {
  final FirebaseAuth _auth = FirebaseAuth.instance;

  bool get isSignedIn => _auth.currentUser != null;

  Future<void> signIn({required String email, required String password}) async {
    await _auth.signInWithEmailAndPassword(email: email, password: password);
    notifyListeners();
  }

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