获取当前视图控制器

- (UIViewController*)topViewControllerWithRootViewController:(UIViewController*)rootViewController

{

   if ([rootViewController isKindOfClass:[UITabBarController class]]) {

       UITabBarController *tabBarController = (UITabBarController *)rootViewController;

       return [self topViewControllerWithRootViewController:tabBarController.selectedViewController];

   } else if ([rootViewController isKindOfClass:[UINavigationController class]]) {

       UINavigationController* navigationController = (UINavigationController*)rootViewController;

       return [self topViewControllerWithRootViewController:navigationController.visibleViewController];

   } else if (rootViewController.presentedViewController) {

       UIViewController* presentedViewController = rootViewController.presentedViewController;

       return [self topViewControllerWithRootViewController:presentedViewController];

   } else {

       return rootViewController;

   }

}