Occurs when the AppBar changes from hidden to visible.
The Opened event's data class is EventArgs.
You can respond to the AppBar being opened by handling the Opened event. This event occurs after the AppBar has been opened 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. To cancel the action, handle the AppBar.Opening event.