如何在UINavigationController上添加视图？

Hi I wondering how should I go about placing a view such that it cover a entire UINavigationController. Basically I want to add a 0.5 alpha, black overlay to the view to give it a 'disabled' look. And the UINavigationController I'm trying to cover is the DetailViewController of the split view controller on the iPad.Hi I wondering how should I go about placing a