# didChangeValue(forKey:withSetMutation:using:) Informs the observed object that the specified change was made to a specified unordered to-many relationship. ``` func didChangeValue(forKey key: String, withSetMutation mutationKind: NSKeyValueSetMutationKind, using objects: Set) ``` ## Parameters `key` The name of a property that is an unordered to-many relationship `mutationKind` The type of change that was made. `objects` The objects that were involved in the change (see ). ## Discussion Use this method when implementing key-value observer compliance manually. Calls to this method are always paired with a matching call to [`willChangeValue(forKey:withSetMutation:using:)`](/documentation/ObjectiveC/NSObject-swift.class/willChangeValue(forKey:withSetMutation:using:)). ### Special Considerations You rarely need to override this method in subclasses, but if you do, be sure to call `super`. --- 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)