A container for information broadcast through a notification center to all registered observers.
- iOS 2.0+
- macOS 10.0+
- UIKit for Mac 13.0+Beta
- tvOS 9.0+
- watchOS 2.0+
A notification contains a name, an object, and an optional dictionary, and is broadcast to by instances of
NSDistributed. The name is a tag identifying the notification. The object is any object that the poster of the notification wants to send to observers of that notification (typically, the object posting the notification). The dictionary stores other related objects, if any.
NSNotification objects are immutable.
The objects of a notification are compared using pointer equality for local notifications. Distributed notifications use strings as their objects, and those strings are compared using
is, because pointer equality doesn’t make sense across process boundaries.
You can subclass
NSNotification to contain information in addition to the notification name, object, and dictionary. This extra data must be agreed upon between notifiers and observers.
NSNotification is a class cluster with no instance variables. As such, you must subclass
NSNotification and override the primitive methods
user. You can choose any designated initializer you like, but be sure that your initializer does not call
NSNotification is not meant to be instantiated directly, and its
init method raises an exception).