手动删除Firebase用户账户后，重启应用仍存旧数据如何解决？

问题场景 #

使用flutter_bloc结合Firebase实现手机认证（phone auth）功能时，遇到异常：手动在Firebase Auth后台删除用户账户后，重启应用时FirebaseAuth.instance.currentUser仍返回已删除的用户信息，而Firebase后台已无该用户记录。

相关代码 #

class AuthCubit extends Cubit<AuthState> {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  AuthCubit() : super(AuthInitialState()) {
    User? currentUser = _auth.currentUser;

    print("The current user is $currentUser");
    print("the current user's uid is : ${currentUser?.uid}");
    print("The current user is ${currentUser?.phoneNumber}");
   
  }
}

运行输出 #

I/flutter (11633): The current user is User(displayName: , email: , emailVerified: false, isAnonymous: false, metadata: UserMetadata(creationTime: 2023-01-21 06:10:04.712Z, lastSignInTime: 2023-01-21 06:10:04.713Z), phoneNumber: +919535334951, photoURL: null, providerData, [UserInfo(displayName: , email: , phoneNumber: +91XXXXXXXX, photoURL: null, providerId: phone, uid: )], refreshToken: , tenantId: null, uid: JhSqO5pZsMbp3vgZA6s1WqjKTU63)
I/flutter (11633): the current user's uid is : JhSqO5pZsMbp3vgZA6s1WqjKTU63
I/flutter (11633): The current user is +91XXXXXXXX

解决方案 #

这是因为Firebase Auth会在本地缓存用户会话信息，后台删除用户后本地缓存不会自动同步失效状态，需主动验证用户有效性：

1. 启动时强制刷新用户状态验证 #

获取currentUser后，调用reload()强制从服务器拉取最新用户状态，若用户已被删除，该方法会抛出异常，此时清除本地会话：

class AuthCubit extends Cubit<AuthState> {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  AuthCubit() : super(AuthInitialState()) {
    _checkCurrentUser();
  }

  Future<void> _checkCurrentUser() async {
    User? currentUser = _auth.currentUser;
    if (currentUser != null) {
      try {
        // 强制从服务器刷新用户信息
        await currentUser.reload();
        // 重新获取刷新后的用户数据
        currentUser = _auth.currentUser;
        if (currentUser == null) {
          emit(AuthUnauthenticatedState());
        } else {
          emit(AuthenticatedState(user: currentUser));
        }
      } catch (e) {
        // 刷新失败，说明用户已被删除，登出清除本地缓存
        await _auth.signOut();
        emit(AuthUnauthenticatedState());
      }
    } else {
      emit(AuthUnauthenticatedState());
    }
  }
}

2. 监听Auth状态实时同步 #

通过authStateChanges()或idTokenChanges()监听用户状态变化，后台用户被删除时本地会及时收到状态更新：

class AuthCubit extends Cubit<AuthState> {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  StreamSubscription? _authSubscription;

  AuthCubit() : super(AuthInitialState()) {
    _listenToAuthChanges();
  }

  void _listenToAuthChanges() {
    _authSubscription = _auth.authStateChanges().listen((User? user) {
      if (user != null) {
        _verifyUserValidity(user);
      } else {
        emit(AuthUnauthenticatedState());
      }
    });
  }

  Future<void> _verifyUserValidity(User user) async {
    try {
      await user.reload();
      final refreshedUser = _auth.currentUser;
      if (refreshedUser == null) {
        emit(AuthUnauthenticatedState());
      } else {
        emit(AuthenticatedState(user: refreshedUser));
      }
    } catch (e) {
      await _auth.signOut();
      emit(AuthUnauthenticatedState());
    }
  }

  @override
  Future<void> close() {
    _authSubscription?.cancel();
    return super.close();
  }
}

3. 强制刷新ID令牌验证 #

使用getIdToken(true)强制刷新令牌，若用户已被删除，该方法会抛出异常，以此判断用户有效性：

Future<bool> _isUserValid(User user) async {
  try {
    await user.getIdToken(true);
    return true;
  } catch (e) {
    return false;
  }
}

启动时调用此方法，返回false则执行signOut()清除本地缓存。

内容的提问来源于stack exchange，提问作者Master Techie