Notification Styles - iOS 8
This notification is sent when a split view controller is expanded or collapsed.
When a view controller is using showViewController:sender: or showDetailViewController:sender:, it may need to know when a split view controller higher in the view hierarchy has changed. UIViewControllerShowDetailTargetDidChangeNotification is sent when a split view controller expands or collapses. The object of this notification is the view controller that caused the change.