Like what Doug mentioned as a comment, you should instead return a Result class from your repository. This is very easy in Kotlin.. but requires more work in Java.

First, create an abstract class Result, with two subclasses, Success and Error.

abstract class Result {}
class Success extends Result {
    private User mUser; // getters/setters omitted for brevity
    public Success(User user) { mUser = user }
}
class Error extends Result {
    private Error mError; // getters/setters omitted for brevity
    public Error(Error error) { mError = error }
}

You can include more details in these classes to better understand what went wrong, but I’m keeping things simple.

Then, in your ViewModel, you should have 2 LiveData values. One for a success, and one for an error. So your AuthViewModel will look like:

public LiveData<User> authenticatedUserLiveData;
public LiveData<Error> userSignInErrorLiveData;

public void signInWithEmail(String email, String password){
    Result result = authRepository.firebaseSignInWithEmail(email, password);
    if (result instanceof Success) {
        authenticatedUserLiveData.value = result.getUser();
    } else if (result instanceof Error) {
        userSignInErrorLiveData.value = result.getError();
    }
}

Finally, you just need to make your AuthRepository return a Result, so the signature will look like:

public Result firebaseSignInWithEmail(String email, String password)

And replace the line authenticatedUserMutableLiveData.setValue(user); with return new Success(user); and replace the logging line with return new Error(authTask.getException);

Hope this helps!

I come from web development so my mobile development with Java isn’t on the right track yet.
I am currently developing an android app using Firebase, for university and I am trying to use clean architecture, and as everything new to me I am coming across some issues.

I’m looking for information on how to handle errors from input in MVVM architecture.
For example, say I am trying to login to Firebase using email and password, the Viewgets the input text and calls the AuthViewModel method signInWithEmail(String email, String password), which calls the AuthRepository method firebaseSignInWithEmail().

Code

SignInFragment

private void signInWithEmail() {
     String emailInput = binding.inputEmail.getText().toString();
     String passwordInput = binding.inputPassword.getText().toString();
     authViewModel.signInWithEmail(emailInput, passwordInput);
     authViewModel.authenticatedUserLiveData.observe(getViewLifecycleOwner(), authenticatedUser ->{
         if(authenticatedUser != null){
             goToHome();
         }
     });
}

AuthViewModel

public LiveData<User> authenticatedUserLiveData;

public void signInWithEmail(String email, String password){
    authenticatedUserLiveData = authRepository.firebaseSignInWithEmail(email, password);
}

AuthRepository

public MutableLiveData<User> firebaseSignInWithEmail(String email, String password) {
        MutableLiveData<User> authenticatedUserMutableLiveData = new MutableLiveData<>();
        firebaseAuth.signInWithEmailAndPassword(email, password)
                .addOnCompleteListener(authTask -> {
                    if(authTask.isSuccessful()){
                        FirebaseUser firebaseUser = firebaseAuth.getCurrentUser();
                    if (firebaseUser != null) {
                        String uid = firebaseUser.getUid();
                        String name = firebaseUser.getDisplayName();
                        String firebaseUserEmail = firebaseUser.getEmail();
                        User user = new User(uid, name, firebaseUserEmail);
                        authenticatedUserMutableLiveData.setValue(user);
                   }
                } else {
                    Log.w(TAG, "signInWithEmail:failure", authTask.getException());
                }
            });
    return authenticatedUserMutableLiveData;
}

What I am trying to accomplish

The “correct” way of getting the ApiException from the AuthRepository, whcih is currently only being logged,

Log.w(TAG, "signInWithEmail:failure", authTask.getException());

and passing it to my AuthViewModel to display the error on a TextView, and not to enter the goToHome().

What I am thinking

I know viewmodel should only act as intermidiary and never have much logic of it’s own.
My first taught was to check if the returned MutableLiveData from the repository method was null, but that left me without the ApiException since the LiveData is of type User, so I cannot return the ApiExcepiton.