A method for sending app-wide messages to anything registered to hear them.
Any object can register for a notification by calling an Notification method for a given key. Any other object can post a notification, immediately alerting the first object of a given event.
Very useful for calling to objects that are unrelated to the sender, such as controllers in separate tabs of a TabBarController. Simultaneously extremely dangerous, since it creates code that is difficult to trace and catch errors from. To be used as a last resort for communicating information.
Registering for a notification:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receiveTestNotification:) name:@"TestNotification" object:nil];
Posting a notification
[[NSNotificationCenter defaultCenter] postNotificationName:@"TestNotification" object:self];