Where to register a ContentObserver which must run indefinitely?

Here is how I am registering a ContentObserver to listen to sent sms:

SendSmsObserver smsObeserver = (new SendSmsObserver(new Handler(), context));
ContentResolver contentResolver = context.getContentResolver();
contentResolver.registerContentObserver(Uri.parse("content://sms"), true, smsObeserver);

This is the SendSmsObserver class:

class SendSmsObserver extends ContentObserver {

private Context context;

SendSmsObserver(Handler handler, Context context) {
    super(handler);
    this.context = context;
}

@Override
public void onChange(boolean selfChange) {
    super.onChange(selfChange);
    queryLastSentSMS();
}

Now the question is that where should I put the top three lines of code? Currently I am writing it in the Activity's OnCreate method. But by doing this I am calling it every time the app is launched. I don't know if it is bad practice or not.

My requirement is that I should listen for sent sms outside my Activity lifecycle. This is working as expected, but should I always register it in the OnCreate method? Also I want to put the same lines in the onReceive() of a BroadcastReceiver to ensure that I am listening after rebooting the device.

UPDATE: BroadcastReceiver is somehow not registering the ContentObserver. I also tried to use getApplicationContext() as a context in BroadcastReceiver but to no avail.

You could create a service that runs indefinitely in the background (Start sticky). In this service you can add your content observer (first 3 lines). This way you ensure that the service is still working after the user closes the app.

You can start this service in the OnCreate of your application class, and also in the broadcast receiver to make sure that it runs after the phone is rebooted.