Question 411646 in Flutter Question posted in
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Flutter – How to pass Exception in sync riverpod provider?

I have a provider which throws an exception which I want to handle where I read the provider:

@Riverpod(dependencies: [firebaseAuth])
User currentUser(CurrentUserRef ref) {
  final user = ref.watch(firebaseAuthProvider).currentUser;
  if (user == null) {
    throw UserNotSignedInException();
  }
  return user;
}

and I want to catch it here:

try {
  ref.read(currentUserProvider);
  resolver.next();
} on UserNotSignedInException {
  logger('User is not logged in, pushing intro route');
  router.push(const IntroRoute());
}

But the Exception is thrown inside the provider and never reaches the catch block. Does somebody know how to pass the exception so I can handle it in the try catch? I know when using AsyncValue that I get an AsyncError to handle but I don’t want an async provider.

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2

Answers


  1. Chosen as BEST ANSWER
    0

    In my case it made most sense to just throw the Exception inside the try catch block. I want to do this because I want to make sure that a user is logged in and don't want to handle a nullable User object.

    @override
void onNavigation(NavigationResolver resolver, StackRouter router) {
  try {
    final user = ref.watch(firebaseAuthProvider).currentUser;
    if (user == null) {
      throw UserNotSignedInException();
    }
    resolver.next();
  } on UserNotSignedInException {
    logger('User is not logged in, pushing intro route', name: 'IntroGuard');
    router.push(const IntroRoute());
  } catch (e, s) {
    logger(
      'Error navigating to intro route',
      error: e,
      stackTrace: s,
      name: 'IntroGuard',
    );
    router.push(const IntroRoute());
  }
}

  2. 0

    You could wrap your User object inside an UserState object with both the User and the Exception or Èrror.

    For example something like this:

    class UserState {
  final User? user;
  final Error? error;

  final get bool isOk => user != null && error == null;

  UserState.success(required this.user);
  UserState.error(required this.error);
}

    And then in your code:

    @Riverpod(dependencies: [firebaseAuth])
UserState currentUser(CurrentUserRef ref) {
  final user = ref.watch(firebaseAuthProvider).currentUser;
  if (user == null) {
    return UserState.error(UserNotSignedInException())
  }
  return UserState.success(user);
}

    and

    final userState = ref.read(currentUserProvider);
if (state.isOk) {
  resolver.next();
} else {
  logger('User is not logged in, pushing intro route');
  router.push(const IntroRoute());
}

    This way, your provider always returns a valid state, whether the User could be obtained or not.

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