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];

这个答案包含了childViewControllers，并维护了一个干净易读的实现。

+ (UIViewController *)topViewController
{
    UIViewController *rootViewController = [UIApplication sharedApplication].keyWindow.rootViewController;

    return [rootViewController topVisibleViewController];
}

- (UIViewController *)topVisibleViewController
{
    if ([self isKindOfClass:[UITabBarController class]])
    {
        UITabBarController *tabBarController = (UITabBarController *)self;
        return [tabBarController.selectedViewController topVisibleViewController];
    }
    else if ([self isKindOfClass:[UINavigationController class]])
    {
        UINavigationController *navigationController = (UINavigationController *)self;
        return [navigationController.visibleViewController topVisibleViewController];
    }
    else if (self.presentedViewController)
    {
        return [self.presentedViewController topVisibleViewController];
    }
    else if (self.childViewControllers.count > 0)
    {
        return [self.childViewControllers.lastObject topVisibleViewController];
    }

    return self;
}

我的问题有点不同，我在我的应用程序中使用SWRevealViewController。 我使用了Yuchen Zhong的答案，但它总是返回topViewController作为SWRevealViewController。对于那些使用SWRevealViewController或其他一些pod来开发侧菜单的人。以下是我对钟宇晨回答的延伸:

extension UIApplication {
class func topViewController() -> UIViewController? {
    var topVC = shared.keyWindow!.rootViewController
    while true {
        if let presented = topVC?.presentedViewController {
            topVC = presented
        } else if let nav = topVC as? UINavigationController {
            topVC = nav.visibleViewController
        } else if let tab = topVC as? UITabBarController {
            topVC = tab.selectedViewController
        }else if let swRVC = topVC as? SWRevealViewController {
            topVC = swRVC.frontViewController
        } else {
            break
        }
    }
    return topVC
}
}

Swift替代解决方案:

static func topMostController() -> UIViewController {
    var topController = UIApplication.sharedApplication().keyWindow?.rootViewController
    while (topController?.presentedViewController != nil) {
        topController = topController?.presentedViewController
    }

    return topController!
}

@implementation UIWindow (Extensions)

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

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

    return topController;
}

@end