Clarification of the exact function of NSNotificationCenter

Question

I'm still picking up ObjC and I'm just trying to make sure I understand the concept of NSNotifications fully:

The [NSNotificationCenter defaultCenter] is a stationary object which is not the sender or the receiver. It merely routes an NSNotification, but in no way, shape, or form handles the event (by default).

Is that correct?

Theory:
Would that allow an AppDelegate to push a notification to the defaultCenter and have something further on in the responder chain / display list (e.g., UITableViewCell) pick up on the action?

Answer 1

Exactly. NSNotificationCenter is just the clearinghouse for the notifications. It keeps track of all the objects observing each notification, so that when a notification is posted, it can be routed to all the right observers.

And yeah, no reason why your AppDelegate can't post a notification that gets picked up by things like a UITableViewCell. NSNotifications are great for situations where an object has to send data to other objects, or tell them that something happened, and you won't know what the recipients should be until runtime.