Async Exception-Handling (Firebase) with the Provider (Flutter) Package

Question

1. The Problem

I'm using a try-catch-finally¹ dynamic to deal with exception handling for Firebase in my simple authentication package for my app. In it, when I receive an error from Firebase's authentication service, I update the labelText on the (custom) TextFormField to show the user that an error occurred.

However, notifyListeners() is apparently being run concurrently to the catch clause, causing the rebuilds to not happen synchronously with exception-handling.

Currently, I'm using ChangeNotifierProvider for basically everything, but should I change to a FutureProvider dynamic. If so, what's the best way of doing it?

---

^{1 I did try using then-catchError-whenComplete also.}

2. The Code

2.1 The Complete Code (Optional)

The complete code is a bit long at this point in the project, but I think that what's shown below will suffice.

At any rate, if you want to check everything out, the whole project is available: flutter_firebase_auth_benchmark.

The relevant files are:

• firebase_auth.dart: the provider class with the relevant data.
• login_screen.dart: the email_field is fed with provider data with the Consumer widget.
• password_reset_workflow.dart: the button that calls the relevant method is put into the LoginScreen through an AnimatedSwitcher.

2.2 The Provider Class

I'm having to use Future.delayed in order to manually synchronize the notifyListeners() and the build() methods — I know, I know, it's very bad...

class Auth extends ChangeNotifier {
  String _errorMsg;

  String get errorMsg => _errorMsg;

  ...

  Future<void> sendPasswordResetWithEmail({@required String email}) async {
    try {
      await FirebaseAuth.instance.sendPasswordResetEmail(email: email);
    } catch(e) {
      switch (e.code) {
        case 'ERROR_USER_NOT_FOUND':
          _errorMsg = 'user not found';
          break;
        default:
          throw UnknownPasswordResetError(
              'Unknown error for password reset with Firebase.');
      }
    } finally {
      notifyListeners();
      await Future.delayed(Duration(milliseconds: 10));
    }
  }
}

2.3 My Custom TextFormField Widget

Something like this is in the app:

return Consumer<Auth>(
  builder: (context, auth, _) {
    return AuthTextFormField(
      ...,
      errorMsgFromServer: auth.errorMsg,
    );
  }
);

Lastly, a validation button uses formKey.currentState.validate() in an if clause to trigger asynchronously await auth.sendPasswordResetWithEmail.

Answer 1

notifyListeners() is apparently being run concurrently to the catch clause

notifyListeners() is inside a finally block, finally will ALWAYS be executed, either if you had an error or not, that's why notifyListeners() is always being called.

Also, using Future.delayed to synchronize events is very bad, you should make another architecture for it.