UnRegister interface callbacks when activity is destroyed

Question

I am working on an Android Application that is entirely dependent on RESTful APIs. Almost every screen of Application is making a network call. I am using following helper class for making network requests.

import android.content.Context;
import android.content.SharedPreferences;
import android.preference.PreferenceManager;
import android.util.Log;

import com.android.volley.AuthFailureError;
import com.android.volley.DefaultRetryPolicy;
import com.android.volley.NetworkResponse;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import java.io.UnsupportedEncodingException;
import java.util.HashMap;
import java.util.Map;

public class RequestHandler {
    private final String deviceID;
    private RequestQueue queue;
    private StringRequest stringRequest;
    private NetworkRequestListener networkRequestListener;
    private NetworkResponseListener networkResponseListener;
    private SharedPreferences sharedPreferences;

    public RequestHandler(Context context) {
        queue = Volley.newRequestQueue(context);
        sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
        deviceID = UtilityMethods.getDeviceId(context);
    }

    public void makeNetworkRequest(String url, int method, final String body) {
        stringRequest = new StringRequest(method, appendedURL,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        Log.e("RESPONSE", response);
                        if (networkResponseListener != null) {
                            networkResponseListener.onResponseLoaded(response);
                        }
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                if (networkResponseListener != null) {
                    networkResponseListener.onResponseFailed(error);
                }
            }
        }) {
            @Override
            public String getBodyContentType() {
                return "application/json; charset=utf-8";
            }

            @Override
            public byte[] getBody() {
                try {
                    return body.getBytes("utf-8");
                } catch (UnsupportedEncodingException | NullPointerException uee) {
                    VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s", body, "utf-8");
                    return null;
                }
            }

            @Override
            public Map<String, String> getHeaders() throws AuthFailureError {
                Map<String, String> headers = new HashMap<>();
                headers.put("version", AppConstants.VERSION);
                headers.put("Content-Type", "application/json");
                return headers;
            }

            @Override
            protected Response<String> parseNetworkResponse(NetworkResponse networkResponse) {
                String response = UtilityMethods.networkResponseToString(networkResponse);

                networkResponseListener.onResponseReceived(response);
                return super.parseNetworkResponse(networkResponse);
            }
        };

        stringRequest.setShouldCache(false);
        stringRequest.setRetryPolicy(new DefaultRetryPolicy(
                0,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        if (networkRequestListener != null) {
            networkRequestListener.beforeMakeRequest(stringRequest);
        }
        queue.add(stringRequest);
    }

    public void setNetworkResponseListener(NetworkResponseListener networkResponseListener) {
        this.networkResponseListener = networkResponseListener;
    }

    public void setNetworkRequestListener(NetworkRequestListener networkRequestListener) {
        this.networkRequestListener = networkRequestListener;
    }

    public RequestQueue getQueue() {
        return queue;
    }

    public StringRequest getStringRequest() {
        return stringRequest;
    }
}

Now issue with this is, that I am not aware of a method to cancel network request (Setting callback interfaces to null isn't working as well). If the response from network call comes after activity being destroyed, the handler methods throw a NPE because of either context being null or a view (Though activity is destroyed the code is still executed). Is there a possible way to cancel/ignore a network response when activity is destroyed? Also If this implementation could be improved as almost every activity is having a memory leak due to this class.

Answer 1

Create a method in this class like this

public static final String TAG = "MyTag";
StringRequest stringRequest; // Assume this exists.
RequestQueue queue;  // Assume this exists.

// Set the tag on the request.
stringRequest.setTag(TAG);

// Add the request to the RequestQueue.
queue.add(stringRequest);

public void cancelTag() {
    return queue.cancelAll(TAG);;
}

In the Activity onStop() call this CancelTag()