Networking with the Volley Library

Overview

Volley is a library that makes networking for Android apps easier and most importantly, faster. Volley Library was announced by Ficus Kirkpatrick at Google I/O '13! It was first used by the Play Store team in Play Store Application and then they released it as an Open Source Library.

Why Volley?

• Volley can pretty much do everything with that has to do with Networking in Android. It has some built-in Requests, such as JsonObjectRequest, JsonArrayRequest, StringRequest etc, based on the generic type of the Request class inside the Library.
• Volley automatically schedule all network requests. It means that Volley will be taking care of all the network requests your app executes for fetching response or image from web.
• Volley provides transparent disk and memory caching.
• Volley provides powerful cancellation request API. It means that you can cancel a single request or you can set blocks or scopes of requests to cancel.
• Volley provides powerful customization abilities.
• Volley provides debugging and tracing tools

Getting started

We need to install volley as a library project. First, download the volley source code:

git clone https://android.googlesource.com/platform/frameworks/volley

and then we need to import the source code into our workspace and then mark it as a library. Now we can add this library as a dependency of any of our apps.

How to use Volley?

Volley has two classes that you will have to deal with:

1. RequestQueue - Requests are queued up here to be executed
2. Request (and any extension of it) - Constructing an network request

A Request object comes in three major types:

• JsonObjectRequest — To send and receive JSON Object from the server
• JsonArrayRequest — To receive JSON Array from the server
• ImageRequest - To receive an image from the server
• StringRequest — To retrieve response body as String (ideally if you intend to parse the response by yourself)

Constructing a RequestQueue

All requests in Volley are placed in a queue first and then processed, here is how you will be creating a request queue:

public MainActivity extends Activty{
	private RequestQueue mRequestQueue;

	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main_screen_layout);
		// ...
		mRequestQueue = Volley.newRequestQueue(this);
		
	}
}

Accessing JSON Data

After this step you are ready to create your Request objects which represents a desired request to be executed. Then we add that request onto the queue.

public class MainActivity extends Activity {
	private RequestQueue mRequestQueue;

        // ...

	private void fetchJsonResponse() {
		// Pass second argument as "null" for GET requests
		JsonObjectRequest req = new JsonObjectRequest("http://ip.jsontest.com/", null,
				new Response.Listener<JSONObject>() {
					@Override
					public void onResponse(JSONObject response) {
						try {
							VolleyLog.v("Response:%n %s", response.toString(4));
							String result = "Your IP Address is " + response.getString("ip");
							Toast.makeText(MainActivity.this, result, Toast.LENGTH_SHORT).show();
						} catch (JSONException e) {
							e.printStackTrace();
						}
					}
				}, new Response.ErrorListener() {
					@Override
					public void onErrorResponse(VolleyError error) {
						VolleyLog.e("Error: ", error.getMessage());
					}
				});

		/* Add your Requests to the RequestQueue to execute */
		mRequestQueue.add(req);
	}

}

And that will execute the request to the server and respond back with the result as specified in the Response.Listener callback.

References

• http://java.dzone.com/articles/android-%E2%80%93-volley-library
• http://arnab.ch/blog/2013/08/asynchronous-http-requests-in-android-using-volley/
• http://files.evancharlton.com/volley-docs/