Get Asynctask response using interface callback in activity and fragment

Asynctask-

public class ConfirmKitAsync extends AsyncTask<String,String,String > {

    static MediaType JSON = MediaType.parse("application/json; charset=utf-8");
    String url;
    RestUserId restUserId;
    ProgressDialog progressDialog;
    IConfirmKitListener responseListener;
    Context context;
    //   String path = null;
    public interface IConfirmKitListener {
        public void callbackConfirmKit(String response);
    }
    public void setConfirmKitListener (IConfirmKitListener listener){
        this.responseListener = listener;
    }

    public ConfirmKitAsync(Context context, String url, RestUserId restUserId) {

        this.context = context;
        this.url = url;
        this.restUserId = restUserId;
   //   path = Uri.parse(url).getPath();   

   //   responseListener = (IConfirmKitListener) context;    

    }

    @Override    

    protected void onPreExecute() {
        super.onPreExecute();
        progressDialog = new ProgressDialog(context);
        progressDialog.setMessage("Loading...");
        progressDialog.setCanceledOnTouchOutside(false);
        progressDialog.setCancelable(false);
        progressDialog.show();
    }

    @Override    

    protected String doInBackground(String... strings) {
        String responseString = null;
        if (isCancelled()) {
            return null;
        } else {
            try {
                Request.Builder builder = new Request.Builder().url(url);
                RequestBody body = RequestBody.create(JSON,
                        new Gson().toJson(restUserId));

                builder.post(body);
                OkHttpClient client = CommonTask.getCommonOkHttpCient();
                client.setConnectTimeout(2, TimeUnit.MINUTES);
                client.setReadTimeout(5, TimeUnit.MINUTES);
                Response response = client.newCall(builder.build()).execute();
                responseString = response.body().string();

                return responseString;
            } catch (SocketTimeoutException e) {

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return responseString;
    }

    @Override    

    protected void onPostExecute(String result) {
        if (result != null) {
            super.onPostExecute(result);
            try {
                responseListener.callbackConfirmKit(result);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        if (progressDialog != null && progressDialog.isShowing()) {
            progressDialog.dismiss();
        }
    }
}

for Activity-

ConfirmKitAsync async= new ConfirmKitAsync (context,  url, restUserId);
async.execute();

for Fragment-

ConfirmKitAsync async= new ConfirmKitAsync(context,  uri, restUserId);
async.setConfirmKitListener(this);
async.execute();

Callback-

@Override
public void callbackConfirmKit(String jsonStr) {
    try {
        if (jsonStr != null && jsonStr.length() > 0) {

            JSONObject jsonObj = new JSONObject(jsonStr);
            JSONObject jObj = jsonObj.getJSONObject("Data");
            jsonArray = jObj.getJSONArray("RestWeapon");

            for (int i = 0; i < jsonArray.length(); i++) {
           }
         }
        }
    catch (JSONException e){
     e.getMessage();
    }
}