Occurs when the AppBar changes from visible to hidden.
The Closed event's data class is EventArgs.
You can respond to hiding the AppBar by handling the Closed event. This event occurs after the AppBar is hidden by an end-user at runtime or in code using the AppBar.IsOpen property. Note that this event provides only a notification, and it is not possible to cancel the action. For this purpose, handle the AppBar.Closing event.