FirebaseAuth_onStart

public override fun onStart() {
        super.onStart()
        // Check if user is signed in (non-null) and update UI accordingly.
        val currentUser = mAuth.currentUser
        val userName = currentUser?.displayName
        textView_username.text = userName
        if(!userName.isNullOrEmpty()){
            setLoginUIVisible(currentUser?.photoUrl)
        }
    }