I have created a number of custom UIViewControllers for UICollectionViewCell programmatically (Apple makes it really easy to create good looking GUI. AutoLayout is not as bad as I heard from the blogsphere. But I digress).

Now I want to be able to have these UIViewController to subscribe to an adhoc NSNotification. I have ensured that there is no typo in the my notification name (The name is defined in a header file). I have also make sure the notification is fired on the main thread, like so:

dispatch_async(dispatch_get_main_queue(),^{
    [[NSNotificationCenter defaultCenter] postNotificationName:NOTIFICATION_NAME object:self];
});

However my UIViewControllers still do not receive any notification at all.

It turns out it is because the controllers instances have gone out of scope. I found out by putting a NSLog in the dealloc method. It proves that the controllers have gone out of scope.

In order to keep them around in memory, I added a NSMutableDictionary to keep reference to these controllers. Will test if it has any adverse effect or not.