- (UIViewController *)topViewController {
UIViewController *resultVC;
resultVC = [self _topViewController:[[UIApplication sharedApplication].keyWindow rootViewController]];
while (resultVC.presentedViewController) {
resultVC = [self _topViewController:resultVC.presentedViewController];
}
return resultVC;
}

• (UIViewController *)_topViewController:(UIViewController *)vc {
  if ([vc isKindOfClass:[UINavigationController class]]) {
  return [self _topViewController:[(UINavigationController *)vc topViewController]];
  } else if ([vc isKindOfClass:[UITabBarController class]]) {
  return [self _topViewController:[(UITabBarController *)vc selectedViewController]];
  } else {
  return vc;
  }
  return nil;
  }