Some details of UIKit

【Some details of UIKit】

一、UIViewController的toolbarItems屬性與UINavigationController配合使用。

　　

二、The view for a navigation controller is just a container for several other views, including a navigation bar, an optional toolbar, and the view containing your custom content.

三、A UIBarButtonItem is a button specialized for placement on a UIToolbar or UINavigationBar object. 

四、navigationItem第一次被引用的時候會被自動建立。只應該在與navigation controller配合的時候使用此屬性。

　　

五、navigation controller --> navigation bar --> navigation item -> bar button item.