获取当前最顶层的ViewController

 - (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;
 }
 使用方法

 UIViewController *topmostVC = [self topViewController];