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Reporting Work Status

This lesson teaches you to

  1. Report Status From an IntentService
  2. Receive Status Broadcasts from an IntentService

You should also read

Try it out

Download the sample

ThreadSample.zip

This lesson shows you how to report the status of a work request run in a background service to the component that sent the request. This allows you, for example, to report the status of the request in an Activity object's UI. The recommended way to send and receive status is to use a LocalBroadcastManager, which limits broadcast Intent objects to components in your own app.

Report Status From an IntentService

To send the status of a work request in an IntentService to other components, first create an Intent that contains the status in its extended data. As an option, you can add an action and data URI to this Intent.

Next, send the Intent by calling LocalBroadcastManager.sendBroadcast(). This sends the Intent to any component in your application that has registered to receive it. To get an instance of LocalBroadcastManager, call getInstance().

For example:

public final class Constants {
    ...
    // Defines a custom Intent action
    public static final String BROADCAST_ACTION =
        "com.example.android.threadsample.BROADCAST";
    ...
    // Defines the key for the status "extra" in an Intent
    public static final String EXTENDED_DATA_STATUS =
        "com.example.android.threadsample.STATUS";
    ...
}
public class RSSPullService extends IntentService {
...
    /*
     * Creates a new Intent containing a Uri object
     * BROADCAST_ACTION is a custom Intent action
     */
    Intent localIntent =
            new Intent(Constants.BROADCAST_ACTION)
            // Puts the status into the Intent
            .putExtra(Constants.EXTENDED_DATA_STATUS, status);
    // Broadcasts the Intent to receivers in this app.
    LocalBroadcastManager.getInstance(this).sendBroadcast(localIntent);
...
}

The next step is to handle the incoming broadcast Intent objects in the component that sent the original work request.

Receive Status Broadcasts from an IntentService

To receive broadcast Intent objects, use a subclass of BroadcastReceiver. In the subclass, implement the BroadcastReceiver.onReceive() callback method, which LocalBroadcastManager invokes when it receives an Intent. LocalBroadcastManager passes the incoming Intent to BroadcastReceiver.onReceive().

For example:

// Broadcast receiver for receiving status updates from the IntentService
private class DownloadStateReceiver extends BroadcastReceiver
{
    // Prevents instantiation
    private DownloadStateReceiver() {
    }
    // Called when the BroadcastReceiver gets an Intent it's registered to receive
    @Override
    public void onReceive(Context context, Intent intent) {
...
        /*
         * Handle Intents here.
         */
...
    }
}

Once you've defined the BroadcastReceiver, you can define filters for it that match specific actions, categories, and data. To do this, create an IntentFilter. This first snippet shows how to define the filter:

// Class that displays photos
public class DisplayActivity extends FragmentActivity {
    ...
    public void onCreate(Bundle stateBundle) {
        ...
        super.onCreate(stateBundle);
        ...
        // The filter's action is BROADCAST_ACTION
        IntentFilter statusIntentFilter = new IntentFilter(
                Constants.BROADCAST_ACTION);

        // Adds a data filter for the HTTP scheme
        statusIntentFilter.addDataScheme("http");
        ...

To register the BroadcastReceiver and the IntentFilter with the system, get an instance of LocalBroadcastManager and call its registerReceiver() method. This next snippet shows how to register the BroadcastReceiver and its IntentFilter:

        // Instantiates a new DownloadStateReceiver
        DownloadStateReceiver mDownloadStateReceiver =
                new DownloadStateReceiver();
        // Registers the DownloadStateReceiver and its intent filters
        LocalBroadcastManager.getInstance(this).registerReceiver(
                mDownloadStateReceiver,
                statusIntentFilter);
        ...

A single BroadcastReceiver can handle more than one type of broadcast Intent object, each with its own action. This feature allows you to run different code for each action, without having to define a separate BroadcastReceiver for each action. To define another IntentFilter for the same BroadcastReceiver, create the IntentFilter and repeat the call to registerReceiver(). For example:

        /*
         * Instantiates a new action filter.
         * No data filter is needed.
         */
        statusIntentFilter = new IntentFilter(Constants.ACTION_ZOOM_IMAGE);
        ...
        // Registers the receiver with the new filter
        LocalBroadcastManager.getInstance(getActivity()).registerReceiver(
                mDownloadStateReceiver,
                statusIntentFilter);

Sending an broadcast Intent doesn't start or resume an Activity. The BroadcastReceiver for an Activity receives and processes Intent objects even when your app is in the background, but doesn't force your app to the foreground. If you want to notify the user about an event that happened in the background while your app was not visible, use a Notification. Never start an Activity in response to an incoming broadcast Intent.

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