NSNotification objects encapsulate information so that it can be broadcast to other objects by an NSNotificationCenter object. An NSNotification object (referred to as a notification) contains a name, an object, and an optional dictionary. 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, it is the object that posted the notification). The dictionary stores other related objects, if any. NSNotification objects are immutable objects.


You can create a notification object with the class methods init(name:object:) or notificationWithName:object:userInfo:. However, you don’t usually create your own notifications directly. The NSNotificationCenter methods post(name:object:) and post(name:object:userInfo:) allow you to conveniently post a notification without creating it first.

Object Comparison

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 isEqual(_:) because pointer equality doesn’t make sense across process boundaries.

Creating Subclasses

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 name, object, and userInfo. You can choose any designated initializer you like, but be sure that your initializer does not call [super init]. NSNotification is not meant to be instantiated directly, and its init method raises an exception.

Nested Types


The type used for the name of a notification.


Creating Notifications

init(name: NSNotification.Name, object: Any?)

Returns a new notification object with a specified name and object.

init(name: NSNotification.Name, object: Any?, userInfo: [AnyHashable : Any]? = nil)

Initializes a notification with a specified name, object, and user information.

Getting Notification Information

var name: NSNotification.Name

The name of the notification.

var object: Any?

The object associated with the notification.

var userInfo: [AnyHashable : Any]?

The user information dictionary associated with the receiver.


Inherits From

See Also

Related Documentation