Type Property

oldKey

If the value of the kindKey entry is NSKeyValueChange.setting, and old was specified when the observer was registered, the value of this key is the value before the attribute was changed.

Declaration

static let oldKey: NSKeyValueChangeKey

Discussion

For NSKeyValueChange.removal or NSKeyValueChange.replacement, if old was specified when the observer was registered, the value is an NSArray instance that contains the objects that have been removed or have been replaced by other objects, respectively.