在xcode里面navigation controller的用处到底是什么！
导航，压栈出栈，衔接Controller，使它们可以来回切换。
A navigation controller manages a stack of view controllers to provide a drill-down interface for hierarchical content. The view hierarchy of a navigation controller is self contained. It is composed of views that the navigation controller manages directly and views that are managed by content view controllers you provide. Each content view controller manages a distinct view hierarchy, and the navigation controller coordinates the navigation between these view hierarchies.
翻译过来就是：navigation controller的作用是调整嵌入在里面的多个view controllers的呈现和返回，完成多级view controller是的嵌套。