how to use delete intent to perform some action on clear notification?

Question

I want to reset a variable of my service when user clears my notification: that's all!

Looking around I see that everyone suggest to add a delete intent on my notification, but intent is used to start an activity, a service o whatever while I just need a thing like this:

void onClearPressed(){
   aVariable = 0;
}

how to obtain this result?

Answer 1

Notifications are not managed by your app and all things like showing notifications and clearing them are actually happening in another process. You can't make another app directly execute a piece of code just because of security reasons.

The only possibility in your case is to provide a PendingIntent which just wraps around a regular Intent and will be started on behalf of your app when notification is cleared. You need to use PendingIntent for sending broadcast or starting a service and then doing what you want in the broadcast receiver or in the service. What exactly to use depends on from which application component you are showing notifications.

In case of broadcast receiver you can just create an anonymous inner class for broadcast receiver and register it dynamically before showing notification. It will look something like that:

public class NotificationHelper {
    private static final String NOTIFICATION_DELETED_ACTION = "NOTIFICATION_DELETED";

    private final BroadcastReceiver receiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            aVariable = 0; // Do what you want here
            unregisterReceiver(this);
        }
    };

    public void showNotification(Context ctx, String text) {
        Intent intent = new Intent(NOTIFICATION_DELETED_ACTION);
        PendingIntent pendintIntent = PendingIntent.getBroadcast(ctx, 0, intent, 0);
        registerReceiver(receiver, new IntentFilter(NOTIFICATION_DELETED_ACTION));
        Notification n = new Notification.Builder(mContext).
          setContentText(text).
          setDeleteIntent(pendintIntent).
          build();
        NotificationManager.notify(0, n);
    }
}

Answer 2

Andrei is correct.
If you want multiple messages back such as:

• you want to know if the message was clicked
• you attached an action with an icon that you want to catch
• AND you want to know if the message was canceled

you must register each of those response filters:

public void showNotification(Context ctx, String text) ()
{
    /… create intents and pending intents same format as Andrie did../
    /… you could also set up the style of your message box etc. …/

    //need to register each response filter
    registerReceiver(receiver, new IntentFilter(CLICK_ACTION));
    registerReceiver(receiver, new IntentFilter(USER_RESPONSE_ACTION));
    registerReceiver(receiver, new IntentFilter(NOTIFICATION_DELETED_ACTION));

    Notification n = new Notification.Builder(mContext)
      .setContentText(text)
      .setContentIntent(pendingIntent)                          //Click action
      .setDeleteIntent(pendingCancelIntent)                     //Cancel/Deleted action
      .addAction(R.drawable.icon, "Title", pendingActionIntent) //Response action
      .build();

    NotificationManager.notify(0, n);

}

Then you can catch the different responses with if, else statements (as Andrei did), or with a switch statement.

Note: I make this response primarily because I could not find this anywhere, and I had to figure it out on my own. (perhaps I will remember it better for that :-) Have Fun!