How to inflate different views in a fragment

Working with fragments in my Java Code I checked if the user is logged into his Firebase Account or not, if he was logged in he got displayed the right View otherwise a "You are not logged in" Fragment got inflated.

public View onCreateView(LayoutInflater inflater, final ViewGroup container,
                         Bundle savedInstanceState) {
    FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
    if (user != null) {
        /**
         * USER IS SIGNED IN
          */

        View view = inflater.inflate(R.layout.fragment_calendar, container, false);
        return view;
       } else {
         /**
         * NO USER IS SIGNED IN
         */

        View view = inflater.inflate(R.layout.fragment_unregistred, container, false);
        return view;
        }
      }

Now doing this in Kotlin somehow seems not to be as easy as it should, it says that "return" is not allowed at the same position as I got it in Java:

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                          savedInstanceState: Bundle?): View? {

    if(getUID.requestUserExistence() != null) {
        FirebaseAuth.getInstance().currentUser!!.getIdToken(true).addOnCompleteListener{task ->
            if(task.isSuccessful) {

                val view = inflater.inflate(R.layout.fragment_crackthecode, container, false)

                return view


            }
        }
    }
}

So why is this happening?

Operator if in Kotlin is an expression. Considering your case we can rewrite it as the following:

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                          savedInstanceState: Bundle?): View? {

    val user = FirebaseAuth.getInstance().getCurrentUser()
    return if (user != null) {
        inflater.inflate(R.layout.fragment_calendar, container, false)
    } else {
        inflater.inflate(R.layout.fragment_unregistred, container, false)
    }
}

Considering your second example in Kotlin it looks different from Java: there is a OnCompleteListener which you can't use to return a View for onCreateView method. If you want return a variable from onCreateView method you shouldn't return it from a callback's (listener's) method. If you rewrite the same code in Java, adding OnCompleteListener, you will get the same or similar error and your code will not be compiled.