Volley AppController class object returning null

Question

I am making an app that makes a JsonObjectRequest and retrieves a JSON data from an URL using the Volley Networking Library for android.

AppController.java

public class AppController extends AppCompatActivity {

    public static final String TAG = AppController.class.getSimpleName();

    private RequestQueue mRequestQueue;

    private static AppController mInstance;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mInstance = this;
    }

    public static synchronized AppController getInstance(){
        return mInstance;
    }

    public RequestQueue getRequestQueue(){
        if(mRequestQueue == null){
            mRequestQueue = Volley.newRequestQueue(getApplicationContext());
        }

        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req) {
        req.setTag(TAG);
        getRequestQueue().add(req);
    }
}

Method in MainActivity.class

private void makeJSONObjectRequest() {

        showDialog();

        JsonObjectRequest jsonObjReq = new JsonObjectRequest(Request.Method.GET,
                urlJsonObj, (String) null, new Response.Listener<JSONObject>() {

            @Override
            public void onResponse(JSONObject response) {
                Log.d(TAG, response.toString());

                try {

                    //Parsing JSON Object response
                    String name = response.getString("name");
                    String email = response.getString("email");
                    JSONObject phone = response.getJSONObject("phone");
                    String home = phone.getString("home");
                    String mobile = phone.getString("mobile");

                    jsonResponse = "";
                    jsonResponse += "Name: " + name + "\n\n";
                    jsonResponse += "Email: " + email + "\n\n";
                    jsonResponse += "Home: " + home + "\n\n";
                    jsonResponse += "Mobile: " + mobile + "\n\n";

                    txtResponse.setTag(jsonResponse);

                }

                catch (JSONException e) {
                    e.printStackTrace();
                    Toast.makeText(getApplicationContext(), "Error: " + e.getMessage(), Toast.LENGTH_SHORT).show();
                }

                hideDialog();
            }
        },

        new ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError volleyError) {
                VolleyLog.d(TAG+"Error:"+ volleyError.getMessage());
                Toast.makeText(getApplicationContext(), volleyError.getMessage(), Toast.LENGTH_SHORT).show();
                hideDialog();
            }
        });

        /*THE ERROR OCCURS HERE! */
        //adding request to the RequestQueue
        AppController.getInstance().addToRequestQueue(jsonObjReq);
    }

It gives the following error:

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.h8pathak.volleyjson.AppController.addToRequestQueue(com.android.volley.Request)' on a null object reference

How can I rectify this code?

Answer 1

Your AppController class needs to extend Application class instead of the AppCompatActivity class.

And remember to update your Manifest as well. ie. Add this class in your AndroidManifest.xml using name attribute for <application> tag.

<application
        android:name=".AppController"/>