我知道已经很晚了，可能是多余的。但以下是我提出的对我有用的片段:

    static func topViewController() -> UIViewController? {
        return topViewController(vc: UIApplication.shared.keyWindow?.rootViewController)
    }

    private static func topViewController(vc:UIViewController?) -> UIViewController? {
        if let rootVC = vc {
            guard let presentedVC = rootVC.presentedViewController else {
                return rootVC
            }
            if let presentedNavVC = presentedVC as? UINavigationController {
                let lastVC = presentedNavVC.viewControllers.last
                return topViewController(vc: lastVC)
            }
            return topViewController(vc: presentedVC)
        }
        return nil
    }

- (UIViewController*)topViewController {
    return [self topViewControllerWithRootViewController:[UIApplication sharedApplication].keyWindow.rootViewController];
}

- (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;
    }
}

我认为Rajesh的解决方案几乎是完美的，但我认为从上到下遍历子视图更好，我改为如下:

+ (UIViewController *)topViewController:(UIViewController *)viewController{

    if (viewController.presentedViewController)
    {

            UIViewController *presentedViewController = viewController.presentedViewController;
            return [self topViewController:presentedViewController];
     } 
     else if ([viewController isKindOfClass:[UITabBarController class]])
     {

            UITabBarController *tabBarController = (UITabBarController *)viewController;
            return [self topViewController:tabBarController.selectedViewController];
    }

         else if ([viewController isKindOfClass:[UINavigationController class]])
    {   

            UINavigationController *navController = (UINavigationController *)viewController;

            return [self topViewController:navController.visibleViewController];
    }

    // Handling UIViewController's added as subviews to some other views.
    else {

        NSInteger subCount = [viewController.view subviews].count - 1;

        for (NSInteger index = subCount; index >=0 ; --index)
        {

            UIView *view = [[viewController.view subviews] objectAtIndex:index];

            id subViewController = [view nextResponder];    // Key property which most of us are unaware of / rarely use.

            if ( subViewController && [subViewController isKindOfClass:[UIViewController class]])
            {
                return [self topViewController:subViewController];
            }
        }
        return viewController;
    }
}

@implementation UIWindow (Extensions)

- (UIViewController*) topMostController
{
    UIViewController *topController = [self rootViewController];

    while (topController.presentedViewController) {
        topController = topController.presentedViewController;
    }

    return topController;
}

@end

之前的答案似乎不能处理rootController是UITabBarController或UINavigationController的情况。

下面是swift中适用于这些情况的函数:

func getCurrentView() -> UIViewController?
{
    if let window = UIApplication.sharedApplication().keyWindow, var currentView: UIViewController = window.rootViewController
    {
        while (currentView.presentedViewController != nil)
        {
            if let presented = currentView.presentedViewController
            {
                currentView = presented
            }
        }

        if currentView is UITabBarController
        {
            if let visible = (currentView as! UITabBarController).selectedViewController
            {
                currentView = visible;
            }
        }

        if currentView is UINavigationController
        {
            if let visible = (currentView as! UINavigationController).visibleViewController
            {
                currentView = visible;
            }
        }

        return currentView
    }

    return nil
}

为了完成Eric的回答(谁省略了弹出窗口，导航控制器，选项卡控制器，视图控制器添加为子视图到一些其他的视图控制器遍历)，这是我的版本返回当前可见的视图控制器:

=====================================================================

- (UIViewController*)topViewController {
    return [self topViewControllerWithRootViewController:[UIApplication sharedApplication].keyWindow.rootViewController];
}

- (UIViewController*)topViewControllerWithRootViewController:(UIViewController*)viewController {
    if ([viewController isKindOfClass:[UITabBarController class]]) {
        UITabBarController* tabBarController = (UITabBarController*)viewController;
        return [self topViewControllerWithRootViewController:tabBarController.selectedViewController];
    } else if ([viewController isKindOfClass:[UINavigationController class]]) {
        UINavigationController* navContObj = (UINavigationController*)viewController;
        return [self topViewControllerWithRootViewController:navContObj.visibleViewController];
    } else if (viewController.presentedViewController && !viewController.presentedViewController.isBeingDismissed) {
        UIViewController* presentedViewController = viewController.presentedViewController;
        return [self topViewControllerWithRootViewController:presentedViewController];
    }
    else {
        for (UIView *view in [viewController.view subviews])
        {
            id subViewController = [view nextResponder];
            if ( subViewController && [subViewController isKindOfClass:[UIViewController class]])
            {
                if ([(UIViewController *)subViewController presentedViewController]  && ![subViewController presentedViewController].isBeingDismissed) {
                    return [self topViewControllerWithRootViewController:[(UIViewController *)subViewController presentedViewController]];
                }
            }
        }
        return viewController;
    }
}

=====================================================================

现在你需要做的就是像下面这样调用上面的方法:

UIViewController *topMostViewControllerObj = [self topViewController];