Returns the ShowNavigationItem Action's item to be chosen when starting up the application.
A ChoiceActionItem object representing the item in the navigation control to be chosen when loading the main window.
This method returns the item which is set for the NavigationItems node's IModelRootNavigationItems.StartupNavigationItem property. If nothing is set for this property, the first visible and enabled item from the first first-level navigation item of the ShowNavigationItem Action's ChoiceActionBase.Items collection is returned.
This method is used by the WinShowStartupNavigationItemController and WebShowStartupNavigationItemController to get a navigation item and emulate clicking it.