willChangeValue(forKey:withSetMutation:using:)
Provides an opportunity to respond when a change is about to be made to a specified to-many relationship.
Declaration
func willChangeValue(forKey inKey: String, withSetMutation inMutationKind: NSKeyValueSetMutationKind, using inObjects: Set<AnyHashable>)Parameters
- inKey:
The name of a property that is a to-many relationship
- inMutationKind:
The type of change that will be made.
- inObjects:
The objects that were involved in the change (see Nskeyvaluesetmutationkind).
Discussion
For more details, see Key-Value Observing Programming Guide.
You must not override this method.