최상위 ViewController 가져오기

+ (UIViewController*)topMostViewController {
  UIViewController *topMostViewController = nil;

  UIViewController *rootViewController =
    [UIApplication sharedApplication].keyWindow.rootViewController;

  if ([rootViewController isKindOfClass:[UINavigationController class]]) {
    UINavigationController *navigationController = (UINavigationController *)rootViewController;
    topMostViewController = navigationController.visibleViewController;
  } else if (rootViewController.presentedViewController) {
    topMostViewController = rootViewController.presentedViewController;
  } else if ([rootViewController isKindOfClass:[UITabBarController class]]) {
    UITabBarController *tabBarController = (UITabBarController *)rootViewController;
    topMostViewController = tabBarController.selectedViewController;

    if ([topMostViewController isKindOfClass:[UINavigationController class]]) {
      UINavigationController *navigationController = (UINavigationController *)topMostViewController;
      topMostViewController = navigationController.visibleViewController;
    }
  } else {
    topMostViewController = rootViewController;
  }

  return topMostViewController;
}