How does the firebase AuthStateListener work?

Question

I am developing an android app using firebase for user management and authentication. I was wondering when the auth state listener gets called and how it works, as in my app I have a bug related to this.

Here is an example of one in my android app:

mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                FirebaseUser user = firebaseAuth.getCurrentUser();
                if (user != null) {
                    // Sign in logic here.
                }
            }
        };

How does the AuthStateListener work and when does it get called?

Solution

As the Firebase API says:

AuthStateListener is called when there is a change in the authentication state.

OnAuthStateChanged gets invoked in the UI thread on changes in the authentication state:

• Right after the listener has been registered
• When a user is signed in
• When the current user is signed out
• When the current user changes
• When there is a change in the current user's token (Notice this has been removed and moved to a separate listener, see FirebaseAuth.IdTokenListener)

Comments

[Tom Finet]

Thank you this really helped me understand! =)

[Firanto]

And how does we suppose to know what happen? on each call? The FirebaseAuth instance didn't tell anything except for currentUser (only whether it exist or null).

[ninbit]

Registering means addAuthStateListener(...) ?

[payne]

The documentation does not mention the 5th element listed in the answer ("When there is a change in the current user's token").

[AL.]

In response to payne, the 5th item has been removed and and moved to a separate listener FirebaseAuth.IdTokenListener (which still includes the rest of the items). @Ami, would suggest to edit it in your answer? Cheers!