willChangeValue(forKey:withSetMutation:using:)
Informs the observed object that the specified change is about to be made to a specified unordered to-many relationship.
Declaration
func willChangeValue(forKey key: String, withSetMutation mutationKind: NSKeyValueSetMutationKind, using objects: Set<AnyHashable>)Parameters
- key:
The name of a property that is an unordered to-many relationship
- mutationKind:
The type of change that will be made.
- objects:
The objects that are involved in the change (see Nskeyvaluesetmutationkind).
Discussion
Use this method when implementing key-value observer compliance manually.
Special Considerations
You rarely need to override this method in subclasses, but if you do, be sure to call super.