Invoking Services Asynchronously from Your Android App

Android doesn’t allow synchronous HTTP requests to be made from the main UI thread. You can use Android’s AsyncTask to make synchronous requests from threads other than the main UI thread. If you don’t want to use AsyncTask, you can make asynchronous requests through the Mobile SDK. To do so, you need to implement and instantiate a callback class, and then set it to the session. When the Mobile SDK makes your service calls for that session, it then makes them asynchronously. To make synchronous calls again, set null as the session’s callback.

With the following steps, this tutorial shows you how to implement asynchronous requests in your Android app:

1. Implement and instantiate your callback class.
2. Set the callback on the session.
3. Call Liferay services.

Now go ahead and get started!

Implementing and Instantiating Your Callback Class

Before implementing and instantiating your callback class, you should add the required imports. The imports you add depend on the return type of the service method you’re calling. For example, if you need to call the service method getGroupEntries to retrieve blog entries from a site’s Blogs portlet, you need to import the Mobile SDK’s AsyncTaskCallback and JSONArrayAsyncTaskCallback:

import com.liferay.mobile.android.task.callback.AsyncTaskCallback;
import com.liferay.mobile.android.task.callback.typed.JSONArrayAsyncTaskCallback;

This is because the getGroupEntries returns a JSONArray. There are multiple AsyncTaskCallback implementations, one for each method return type:

• JSONObjectAsyncTaskCallback
• JSONArrayAsyncTackCallback
• StringAsyncTaskCallback
• BooleanAsyncTaskCallback
• IntegerAsyncTaskCallback
• LongAsyncTaskCallback
• DoubleAsyncTaskCallback

It’s also possible to use a generic AsyncTaskCallback implementation called GenericAsyncTaskCallback. To do so, you must implement a transform method and handle JSON parsing yourself.

If you still don’t want to use any of these callbacks, you can implement AsyncTaskCallback directly. However, you should be careful when doing so. You should always get the first element of the JSONArray passed as a parameter to the onPostExecute(JSONArray jsonArray) method (for example, jsonArray.get(0)).

Next, implement and instantiate your callback class. When implementing your callback class, you need to implement its onFailure and onSuccess methods. These methods respectivley determine what your app does when the request fails or succeeds. The onFailure() method is called if an exception occurs during the request. This could be triggered by a connection exception (e.g., a request timeout) or a ServerException. If a ServerException occurs, it’s because something went wrong on the server side. For example, if you pass a groupId that doesn’t exist, the portal complains about it, and the Mobile SDK wraps the error message with ServerException.

The onSuccess method is called on the main UI thread after the request finishes. Since the request is asynchronous, the service call immediately returns a null object. The service delivers the service’s real return value to the callback’s onSuccess() method, instead.

Example code is shown here for AsyncTaskCallback and JSONArrayAsyncTaskCallback:

AsyncTaskCallback callback = new JSONArrayAsyncTaskCallback() {

    public void onFailure(Exception exception) {
        // Implement exception handling code
    }

    public void onSuccess(JSONArray result) {
        // Called after request has finished successfully
    }

};

Now that you have your callback class, you can set it to the session.

Setting the Callback to the Session

Once you’ve implemented and instantiated your callback class, you’re ready to set it to the session. If you haven’t created a session yet, do so now. The tutorial Invoking Liferay Services in Your Android App shows you how to create a session. Now you’re ready to set the callback to the session. For example, this is done here for AsyncTaskCallback:

session.setCallback(callback);

Pretty simple! Now you’re ready to make the service call.

Making the Service Call

Last but certainly not least, make the service call. This is done the same as calling any other service: create a service object from the session and use it to make the service call. This is also described in the tutorial Invoking Liferay Services in Your Android App. An example service call that gets all the blog entries from a site’s Blogs portlet is shown here:

service.getGroupEntries(10184, 0, 0, -1, -1);

The example code from the above sections is shown together here:

import com.liferay.mobile.android.task.callback.AsyncTaskCallback;
import com.liferay.mobile.android.task.callback.typed.JSONArrayAsyncTaskCallback;

...

AsyncTaskCallback callback = new JSONArrayAsyncTaskCallback() {

    public void onFailure(Exception exception) {
        // Implement exception handling code
    }

    public void onSuccess(JSONArray result) {
        // Called after request has finished successfully
    }

};

// create a session first
session.setCallback(callback);

// create a service object first
service.getGroupEntries(10184, 0, 0, -1, -1);

Great! Now you know how to invoke services asynchronously from your Android app.

Related Topics

Creating iOS Apps that Use Liferay

Building Mobile SDKs

Service Builder and Services