The identifier string of the action that the user selected.
- iOS 10.0+
- macOS 10.14+Beta
- watchOS 3.0+
This parameter may contain one the identifier of one of your
UNNotification objects or it may contain a system-defined identifier. The system defined identifiers are
UNNotification, which indicate that the user opened the app or dismissed the notification without any further actions.
For more information about defining custom actions, see Declaring Your Actionable Notification Types.