android studio firebase how to add username code example

Example 1: how to check if user is logged in firebase android and then load another activity

private FirebaseAuth firebaseAuth;
 FirebaseAuth.AuthStateListener mAuthListener;
    firebaseAuth = FirebaseAuth.getInstance();

      mAuthListener = new FirebaseAuth.AuthStateListener(){
                @Override
                public  void  onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth){
            FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
        if(user!=null){
        Intent intent = new Intent(LoginActivity.this, MainActivity.class);
        startActivity(intent);
        finish();
}
                }


            };

Example 2: firebase auth update

In the newest version of firebase_auth:

FirebaseUser has been changed to User

AuthResult has been changed to UserCredential

GoogleAuthProvider.getCredential() has been changed to GoogleAuthProvider.credential()

onAuthStateChanged which notifies about changes to the user's sign-in state was replaced with authStateChanges()

currentUser() which is a method to retrieve the currently logged in user, was replaced with the property currentUser and it no longer returns a Future