If specified, a notification should be sent to the observer immediately, before the observer registration method even returns.
- iOS 2.0+
- macOS 10.5+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 2.0+
The change dictionary in the notification will always contain an
new entry if
new is also specified but will never contain an
old entry. (In an initial notification the current value of the observed property may be old, but it's new to the observer.) You can use this option instead of explicitly invoking, at the same time, code that is also invoked by the observer's
observe method. When this option is used with
add a notification will be sent for each indexed object to which the observer is being added.