Allows you to prevent an item from being selected.
The SelectedItemChanging event's data class is DevExpress.XtraBars.Navigation.SelectedItemChangingEventArgs.
By default, when an end-user clicks an item, it is selected, provided that the item selection feature is enabled (see OfficeNavigationBar.AllowItemSelection). You can prevent a certain item from being selected by handling the SelectedItemChanging event and setting the event's Cancel parameter to true.
After the item is selected, the OfficeNavigationBar.SelectedItemChanged event fires. This is only a notification event.