# didChangeValue(forKey:withSetMutation:using:) Provides an opportunity to respond when a change was made to a specified to-many relationship. ``` func didChangeValue(forKey inKey: String, withSetMutation inMutationKind: NSKeyValueSetMutationKind, using inObjects: Set) ``` ## Parameters `inKey` The name of a property that is a to-many relationship. `inMutationKind` The type of change that was made. `inObjects` The objects that were involved in the change (see ). ## Discussion For more details, see [Key-Value Observing Programming Guide](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/KeyValueObserving/KeyValueObserving.html#//apple_ref/doc/uid/10000177i). You must not override this method. --- 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)