另一个Swift解决方案

extension UIViewController {
    static var topmostViewController: UIViewController? {
        return UIApplication.sharedApplication().keyWindow?.topmostViewController
    }

    var topmostViewController: UIViewController? {
        return presentedViewController?.topmostViewController ?? self
    }
}

extension UINavigationController {
    override var topmostViewController: UIViewController? {
        return visibleViewController?.topmostViewController
    }
}

extension UITabBarController {
    override var topmostViewController: UIViewController? {
        return selectedViewController?.topmostViewController
    }
}

extension UIWindow {
    var topmostViewController: UIViewController? {
        return rootViewController?.topmostViewController
    }
}

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()

iOS 4在UIWindow上引入了rootViewController属性:

[UIApplication sharedApplication].keyWindow.rootViewController;

你需要在创建视图控制器后自己设置。

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
    }
}

你应该使用:

[UIApplication sharedApplication].window.rootViewController;

当[UIApplication sharedApplication]上有一个uiactionsheet时。keyWindow，这是不正确的使用keyWindow在这个答案中提到。

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;
}