获取tabbarController中tabbarItem的NavigationController堆栈

我需要获取UIViewControllers的列表，比如UINavigationController在指定的 UITabBarController中tabbaritem的索引。请帮忙~

这个：

NSArray *arrControllers = self.tabBarController.viewControllers;
for(UIViewController *viewController in arrControllers)
{
   if([viewController isKIndOfClass:[UINavigationController class]])
   {
     //NavigationController
     UINavigationController *navCtrl = (UINavigationController *)viewController;
     NSLog(@"%@",navCtrl.viewControllers);
   }
   else
   {
     // view controller
   }
}