Android Volley Returning results twice for one request

Question

I have been trying to figure out this issue for two days now and I am completly stumped. For some reason I am sending one request to the queue but volley is returning it tw

Answer 1

To stop the multiple request you can configure retry policy for your request object by using the setRetryPolicy() method of the request object. I managed to do this with following code:

req.setRetryPolicy(new DefaultRetryPolicy(20 * 1000, 0,
      DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));

With the above code, i reduced the timeout to 2 seconds and set the number of retries to 0.

Answer 2

Okay I faced the issue and came up with a solution. In my custom class i created a global variable on top as you can see in below code

MyRequest extends StringRequest {
    private boolean mDelivered;  //boolean to deliver response only once

then in constructor i initialsed it

    public MyRequest(String url, Listener<String> listener,
                      ErrorListener errorListener, Context ctx) {
    super(url, listener, errorListener);
    mContext = ctx.getApplicationContext();
    mDelivered = false;
    DefaultRetryPolicy retryPolicy = new DefaultRetryPolicy(5000, 1, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT);
    setRetryPolicy(retryPolicy);
}

and finally i overrided deliverResponse method. For first time mDelivered will be false and once it's delivered it'll be true. if response delivered from cache then cancel network request

    @Override
protected void deliverResponse(String response) {
    if (!mDelivered) {
        mDelivered  = true;
        cancel();   //if cache delivers response better to cancel scheduled network request
        super.deliverResponse(response);
    }
}

Hope this helps

Answer 3

I believe I have figured it out after stepping through the code more. I believe it is the softttl that is causing this behavior. In the Volley cachedispatcher

            if (!entry.refreshNeeded()) {
                // Completely unexpired cache hit. Just deliver the response.
                mDelivery.postResponse(request, response);
            } else {
                // Soft-expired cache hit. We can deliver the cached response,
                // but we need to also send the request to the network for
                // refreshing.
                request.addMarker("cache-hit-refresh-needed");
                request.setCacheEntry(entry);

                // Mark the response as intermediate.
                response.intermediate = true;

                // Post the intermediate response back to the user and have
                // the delivery then forward the request along to the network.
                mDelivery.postResponse(request, response, new Runnable() {
                    @Override
                    public void run() {
                        try {
                            mNetworkQueue.put(request);
                        } catch (InterruptedException e) {
                            // Not much we can do about this.
                        }
                    }
                });

This posts the response then sends it to the network which posts another response to the same listener.