First response from server always null with AsyncTask

Issue

I've setup a MySql server with a RESTful api to handle my login/signup system for my android app.

I'm creating an ASyncTask to handle the signup POST request, the server should return a JSON object telling us whether it was successful or not. When I input valid details and register on my Android app, the first response in onPostExecute is null. I press the button again and it is correct. What could I be doing wrong?

private class PostAndReadResponseTask extends AsyncTask<Account, Void, String> {
    @Override
    protected String doInBackground(Account... accounts) {
        final Account thisAccount = accounts[0];
        RequestQueue requestQueue = Volley.newRequestQueue(RegisterActivity.this);
        final String signupURL = "http://localhost:8080/fitnessTrack/api.php?apicall=signup";

        StringRequest stringRequest = new StringRequest(Request.Method.POST, signupURL, new Response.Listener<String>() {

            @Override
            public void onResponse(String response) {
                responseJSON = response;
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.e("Volley Error:", error.getMessage());
            }
        }) {
            @Override
            protected Map<String, String> getParams() {
                Map<String, String> params = new HashMap<String, String>();
                params.put("username", thisAccount.getUsername());
                params.put("password", thisAccount.getPassword());
                params.put("email", thisAccount.getEmail());
                params.put("firstname", thisAccount.getFirstName());
                return params;
            }
        };
        requestQueue.add(stringRequest);
        return responseJSON;
    }

    @Override
    protected  void onPostExecute(String result) {
        System.out.println(result);
    }
}

FYI: I edited the URL to say localhost, even though I'm using my own external IP. Even when the response is null, the database does update with the signup data.

Solution

The responseJSON is only updated here

@Override
public void onResponse(String response) { 
    responseJSON = response; // update UI using responseJSON in here
}

so it won't be ready until that method is called with the response. Try printing in there and it should work

Answered By - Kevin