Creating a Background Service

The IntentService class provides a straightforward structure for running an operation on a single background thread. This allows it to handle long-running operations without affecting your user interface's responsiveness. Also, an IntentService isn't affected by most user interface lifecycle events, so it continues to run in circumstances that would shut down an AsyncTask

An IntentService has a few limitations:

• It can't interact directly with your user interface. To put its results in the UI, you have to send them to an Activity.
• Work requests run sequentially. If an operation is running in an IntentService, and you send it another request, the request waits until the first operation is finished.
• An operation running on an IntentService can't be interrupted.

However, in most cases an IntentService is the preferred way to perform simple background operations.

This lesson shows you how to create your own subclass of IntentService. The lesson also shows you how to create the required callback method onHandleIntent(). Finally, the lesson describes shows you how to define the IntentService in your manifest file.

Create an IntentService

To create an IntentService component for your app, define a class that extends IntentService, and within it, define a method that overrides onHandleIntent(). For example:

public class RSSPullService extends IntentService {
    @Override
    protected void onHandleIntent(Intent workIntent) {
        // Gets data from the incoming Intent
        String dataString = workIntent.getDataString();
        ...
        // Do work here, based on the contents of dataString
        ...
    }
}

Notice that the other callbacks of a regular Service component, such as onStartCommand() are automatically invoked by IntentService. In an IntentService, you should avoid overriding these callbacks.

Define the IntentService in the Manifest

An IntentService also needs an entry in your application manifest. Provide this entry as a <service> element that's a child of the <application> element:

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name">
        ...
        <!--
            Because android:exported is set to "false",
            the service is only available to this app.
        -->
        <service
            android:name=".RSSPullService"
            android:exported="false"/>
        ...
    <application/>

The attribute android:name specifies the class name of the IntentService.

Notice that the <service> element doesn't contain an intent filter. The Activity that sends work requests to the service uses an explicit Intent, so no filter is needed. This also means that only components in the same app or other applications with the same user ID can access the service.

Now that you have the basic IntentService class, you can send work requests to it with Intent objects. The procedure for constructing these objects and sending them to your IntentService is described in the next lesson.