Fires when the NavigationFrame is about to change its currently selected page and allows you to cancel this upcoming modification.
The SelectedPageChanging event's data class is DevExpress.XtraBars.Navigation.SelectedPageChangingEventArgs.
Handle the SelectedPageChanging event and set the Cancel property to true to restrict the frame navigation to the specific NavigationPage. If not canceled, the NavigationFrame.SelectedPageChanged event occurs.
The current selection in the frame page is stored in the NavigationFrame.SelectedPage property.