# addObserver(_:selector:name:object:) Adds an entry to the notification center’s dispatch table with an observer, a selector, and an optional notification name and sender. ``` func addObserver(_ observer: Any, selector aSelector: Selector, name aName: NSNotification.Name?, object anObject: String?) ``` ## Parameters `observer` An object registering as an observer. `aSelector` A selector that the notification center sends `notificationObserver` to notify when posting the notification. `aName` The name of the notification for which to register the observer; that is, only notifications with this name are delivered to the observer. When `nil`, the notification center doesn’t use a notification’s name to decide whether to deliver it to the observer. `anObject` The object whose notifications the observer wants to receive; that is, only notifications sent by this sender are delivered to the observer. When `nil`, the notification center doesn’t use a notification’s sender to decide whether to deliver it to the observer. ## Discussion This method calls [`addObserver(_:selector:name:object:suspensionBehavior:)`](/documentation/Foundation/DistributedNotificationCenter/addObserver(_:selector:name:object:suspensionBehavior:)), passing [`DistributedNotificationCenter.SuspensionBehavior.coalesce`](/documentation/Foundation/DistributedNotificationCenter/SuspensionBehavior/coalesce) for `suspensionBehavior`. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)