willChange(_:valuesAt:forKey:)
Informs the observed object that the specified change is about to be executed at given indexes for a specified ordered to-many relationship.
Declaration
func willChange(_ changeKind: NSKeyValueChange, valuesAt indexes: IndexSet, forKey key: String)Parameters
- changeKind:
The type of change that is about to be made.
- indexes:
The indexes of the to-many relationship that will be affected by the change.
- key:
The name of a property that is an ordered to-many relationship.
Discussion
Use this method when implementing key-value-observing compliance manually.
Special Considerations
You rarely need to override this method in subclasses, but if you do, be sure to call super.