iphone下toolbar的使用
IOS 3.0以后，navigation controller自带toolbar, 原文如下：“In iOS 3.0 and later, a navigation interface can display a toolbar and populate it with items provided by the currently visible view controller. The toolbar itself is managed by the navigation controller object.”
显示toolbar以及toolbar基本的设置代码如下：

具体解释的原文为：
“To hide the toolbar for a specific view controller, set the hidesBottomBarWhenPushed property of that view controller to YES. When the navigation controller encounters a view controller with this property set to YES, it generates an appropriate transition animation whenever the view controller is pushed onto (or removed from) the navigation stack.”