kindKey
An NSNumber object that contains a value corresponding to one of the Nskeyvaluechange enums, indicating what sort of change has occurred.
Declaration
static let kindKey: NSKeyValueChangeKeyDiscussion
A value of NSKeyValueChange.setting indicates that the observed object has received a setValue(_:forKey:) message, or that the key-value-coding-compliant set method for the key has been invoked, or that one of the willChangeValue(forKey:) or didChangeValue(forKey:) methods has otherwise been invoked.
A value of NSKeyValueChange.insertion, NSKeyValueChange.removal, or NSKeyValueChange.replacement indicates that mutating messages have been sent a key-value observing compliant collection proxy, or that one of the key-value-coding-compliant collection mutation methods for the key has been invoked, or a collection will change or did change method has been otherwise been invoked.
You can use the uintValue method on the NSNumber object to retrieve the value of the change kind.