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 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.