UIController 跳转

对于UINavigationController 的跳转，系统有三个方法：

- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated; // Uses a horizontal slide transition. Has no effect if the view controller is already in the stack.

- (UIViewController *)popViewControllerAnimated:(BOOL)animated; // Returns the popped controller.返回上一级controller，弹出当前controller

- (NSArray *)popToViewController:(UIViewController *)viewController animated:(BOOL)animated; // Pops view controllers until the one specified is on top. Returns the popped controllers.弹出视图控制器上,直到一个指定。返回了控制器。

- (NSArray *)popToRootViewControllerAnimated:(BOOL)animated; // Pops until there's only a single view controller left on the stack. Returns the popped controllers.返回到给视图控制器