一个完整的非递归版本，照顾到不同的场景:

视图控制器正在呈现另一个视图 视图控制器是一个UINavigationController 视图控制器是一个UITabBarController

objective - c

 UIViewController *topViewController = self.window.rootViewController;
 while (true)
 {
     if (topViewController.presentedViewController) {
         topViewController = topViewController.presentedViewController;
     } else if ([topViewController isKindOfClass:[UINavigationController class]]) {
         UINavigationController *nav = (UINavigationController *)topViewController;
         topViewController = nav.topViewController;
     } else if ([topViewController isKindOfClass:[UITabBarController class]]) {
         UITabBarController *tab = (UITabBarController *)topViewController;
         topViewController = tab.selectedViewController;
     } else {
         break;
     }
 }

斯威夫特 4+

extension UIWindow {
    func topViewController() -> UIViewController? {
        var top = self.rootViewController
        while true {
            if let presented = top?.presentedViewController {
                top = presented
            } else if let nav = top as? UINavigationController {
                top = nav.visibleViewController
            } else if let tab = top as? UITabBarController {
                top = tab.selectedViewController
            } else {
                break
            }
        }
        return top
    }
}

以下是对我有效的方法。

我发现有时候控制器在键窗口上是nil，因为键窗口是一些操作系统的东西，如警报等。

 + (UIViewController*)topMostController
 {
     UIWindow *topWndow = [UIApplication sharedApplication].keyWindow;
     UIViewController *topController = topWndow.rootViewController;

     if (topController == nil)
     {
         // The windows in the array are ordered from back to front by window level; thus,
         // the last window in the array is on top of all other app windows.
         for (UIWindow *aWndow in [[UIApplication sharedApplication].windows reverseObjectEnumerator])
         {
             topController = aWndow.rootViewController;
             if (topController)
                 break;
         }
     }

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

     return topController;
 }

我认为大多数答案都完全忽略了UINavigationViewController，所以我用下面的实现来处理这个用例。

+ (UIViewController *)topMostController {
    UIViewController * topController = [UIApplication sharedApplication].keyWindow.rootViewController;
    while (topController.presentedViewController || [topController isMemberOfClass:[UINavigationController class]]) {
        if([topController isMemberOfClass:[UINavigationController class]]) {
            topController = [topController childViewControllers].lastObject;
        } else {
            topController = topController.presentedViewController;
        }
    }

    return topController;
}

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
}
}

使用下面的扩展抓取当前可见的UIViewController。适用于Swift 4.0及更高版本

Swift 4.0及以上版本:

extension UIApplication {
    
    class func topViewController(_ viewController: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
        if let nav = viewController as? UINavigationController {
            return topViewController(nav.visibleViewController)
        }
        if let tab = viewController as? UITabBarController {
            if let selected = tab.selectedViewController {
                return topViewController(selected)
            }
        }
        if let presented = viewController?.presentedViewController {
            return topViewController(presented)
        }
        return viewController
    }
}

如何使用?

let objViewcontroller = UIApplication.topViewController()

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;
    }
}