Tuesday, October 6, 2009

Broadcast Receivers | Android Developer Tutorial (Part 11)

The concept of Broadcast Receivers, one of the fundamental blocks of Android, is very simple. These are applications that will respond to any intent that is broadcast by other applications. Provided the broadcast intent matches the intent specified against the receiver in the AndroidManifest.xml

This goes to automatically imply that many activities, events, services or the like can broadcast intents expecting the appropriate action to be automatically taken. So, to begin with, let us see the various Broadcast events that are given by the platform itself. Here is a standard list obtained from the android documentation:


For details on when each of these intents get broadcasted, please see the android documentation. I have chosen the BROADCAST event ACTION_TIME_CHANGED as I can simulate a time change in the emulator. How to simulate the time change from adb shell is given at the end of this tutorial.

Now let us get on to the example of a broadcast receiver. You can download the complete code here.

Any activity that intends to respond to broadcasts has to extend the android.content.BroadcastReceiverclass and implement the single method onReceive().

In my example, I just notify on the status bar that the time has changed and the moment the user clicks on the status bar and sees the details, clicks on the details, the notification is removed from the status bar.

When the user clicks on the detailed portion, I take the user to the contacts application, just for anything better. Ideally this should take to an activity relevant to the application. So, if you see the onReceive()method, it is nothing but a notification example. That is all.

      private NotificationManager mNotificationManager;
      private int SIMPLE_NOTFICATION_ID;
      public void onReceive(Context context, Intent intent) {

        mNotificationManager = (NotificationManager)context.getSystemService(Context.NOTIFICATION_SERVICE);
      Notification notifyDetails = new Notification(,"Time Reset!",System.currentTimeMillis());
      PendingIntent myIntent = PendingIntent.getActivity(context, 0, new Intent(Intent.ACTION_VIEW, People.CONTENT_URI), 0);
      notifyDetails.setLatestEventInfo(context, "Time has been Reset", "Click on me to view Contacts", myIntent);
      notifyDetails.flags |= Notification.FLAG_AUTO_CANCEL;
      mNotificationManager.notify(SIMPLE_NOTFICATION_ID, notifyDetails);
            Log.i(getClass().getSimpleName(),"Sucessfully Changed Time");


Once this class is ready, start the android emulator in eclipse. Then, simulate a time changed from the command prompt as given below. You will see the notification come up.

Simulating a time change in the emulator:

To start the adb shell type (in windows, assuming the path has been set to the tools folder of android sdk installation):

C:\> adb shell
#date –- 2009-10-01 14:24:59
#date –s 20070325.123456

The first step date –-gives the time in seconds since Jan 1st 1970. Take the result and give it as a parameter to date –s, the time is reset in adb and within a minute on the android emulator. This broadcasts the event that time has been changed in the emulator and kicks off the Broadcast Receiver program that has been executed.

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