UITabBarController - 如何访问视图控制器？

I have a uitabbarcontroller, which contains multiple tabs and viewControllers. I am trying to loop through the view controllers to find the right one and call a method. but the type of the view controller i get, each time i go through the loop is a UINavigationController. So how can i simply access a view controller in my tabBar?I have a uitabbarcontroller, which contains mul