willChangeValue(forKey:)
Informs the observed object that the value of a given property is about to change.
Declaration
func willChangeValue(forKey key: String)Parameters
- key:
The name of the property that will change.
Discussion
Use this method when implementing key-value observer compliance manually to inform the observed object that the value at key is about to change.
The change type of this method is NSKeyValueChangeSetting.
Special Considerations
You rarely need to override this method in subclasses, but if you do, be sure to call super.