Facebook/Android - how to check whether the user has already been registered, and now just log them in

I am having trouble implementing Facebook login/register with Android. The documentation is not sufficient, and their use case is strange (all they talk about is fragments there and this gets attention away from the main subject)

What I have created is working login(registration) but If I dont have a check whether the user is already logged in, so the app tries to insert them into the db anew, resulting in an error.

Also I dont know what uiHelper is for so I've completely removed it from my code.

My question is how to check whether the user has already been registered via Facebook and now just log them in.

EDIT: what Im trying to say is that the user is not logged in in both cases, but in one of the cases, they have already registered via fb, and I want to just log them in. In the other case they havent registered via fb and its their first approach, so I want to register them in the database and log them in (I've already accomplished the latter)

@Override
    public void onClick(View v) {
        int id = v.getId();
        if (id == R.id.authButton) {
            OpenRequest openrequest = new OpenRequest(this).setPermissions(Arrays.asList("basic_info", "email", "user_likes", "user_status"));
            Session session = new Session(Login.this);
            session.openForRead(openrequest);
}

private Session.StatusCallback callback = new Session.StatusCallback() {
    @Override
    public void call(Session session, SessionState state, Exception exception) {
        onSessionStateChange(session, state, exception);
    }
};

private void onSessionStateChange(Session session, SessionState state, Exception exception) {

    if (state.isOpened()) {
         makeMeRequest(session);
    } else if (state.isClosed()) {

        System.out.println("closed"); //debugging
        Session sessionw = new Session(this);
        Session.setActiveSession(sessionw);
        sessionw.openForRead(new Session.OpenRequest(this).setCallback(callback).setPermissions(Arrays.asList("basic_info", "email", "user_likes", "user_status")));
    }
}


private void makeMeRequest(final Session session) {
    // Make an API call to get user data and define a 
    // new callback to handle the response.
    Request request = Request.newMeRequest(session, new Request.GraphUserCallback() {
        @Override
        public void onCompleted(GraphUser user, Response response) {
            // If the response is successful
            if (session == Session.getActiveSession()) {
                if (user != null) {
                    userFBId = user.getId();
                    userName = user.getName();
                    userEmail = (String) user.asMap().get("email");
                    userSex = (String) user.getProperty("gender");
                    userFacebookAvatar = "http://graph.facebook.com/"+user.getId()+"/picture?type=square";

                    new RegisterFacebookUser(Login.this, Login.this, userName, userEmail, userSex, userFacebookAvatar).execute(); //this is an async task that inserts the user in the db
                }
            }
            if (response.getError() != null) {
                System.out.println(response.getError().toString());
            }
        }
    });
    request.executeAsync();
} 


@Override 
public void OnFacebookUserRegisteredSuccess(int userId) {
    editor = sharedPrefs.edit();
    editor.putBoolean("userLoggedInState", true);
    editor.putBoolean("userHasRegisteredViaFacebook", true);
    editor.putInt("currentLoggedInUserId", userId);
    editor.putString("userFBId", userFBId);
    editor.commit();
    Intent signupSuccessHome = new Intent(this, Home.class);
    startActivity(signupSuccessHome);
    finish();

}

@Override
public void OnFacebookUserRegisteredFailure() {

    toastMaker.toast(net.asdqwe.activities.Login.this, Configurationz.ErrorMessages.FACEBOOK_LOGIN_FAILURE, Toast.LENGTH_LONG);
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == REAUTH_ACTIVITY_CODE) {
       Session.getActiveSession().onActivityResult(Login.this, requestCode, resultCode, data);
    } else {

        Session session = Session.getActiveSession();
        int sanitizedRequestCode = requestCode % 0x10000;
        session.onActivityResult(this, sanitizedRequestCode, resultCode, data);

    }
}