在一个非常罕见的情况下，使用自定义segue，最顶层的视图控制器不在导航堆栈或选项卡栏控制器中或被呈现，但它的视图被插入到关键窗口子视图的顶部。

在这种情况下，有必要检查UIApplication.shared.keyWindow.subviews.last == self。视图来确定当前视图控制器是否是最顶端的。

class func topViewController(controller: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
        if let navigationController = controller as? UINavigationController {
            return topViewController(controller: navigationController.visibleViewController)
        }
        if let tabController = controller as? UITabBarController {
            if let selected = tabController.selectedViewController {
                return topViewController(controller: selected)
            }
        }
        if let presented = controller?.presentedViewController {
            return topViewController(controller: presented)
        }
        return controller
    }

在一个非常罕见的情况下，使用自定义segue，最顶层的视图控制器不在导航堆栈或选项卡栏控制器中或被呈现，但它的视图被插入到关键窗口子视图的顶部。

在这种情况下，有必要检查UIApplication.shared.keyWindow.subviews.last == self。视图来确定当前视图控制器是否是最顶端的。

太多口味了，但都不是一种反复精心制作的。结合前面的内容:

     func topMostController() -> UIViewController? {
        var from = UIApplication.shared.keyWindow?.rootViewController
        while (from != nil) {
            if let to = (from as? UITabBarController)?.selectedViewController {
                from = to
            } else if let to = (from as? UINavigationController)?.visibleViewController {
                from = to
            } else if let to = from?.presentedViewController {
                from = to
            } else {
                break
            }
        }
        return from
    }

presentViewController显示一个视图控制器。它不会返回一个视图控制器。如果你不使用UINavigationController，你可能正在寻找presenttedviewcontroller，你需要从根开始，向下迭代所呈现的视图。

if var topController = UIApplication.sharedApplication().keyWindow?.rootViewController {
    while let presentedViewController = topController.presentedViewController {
        topController = presentedViewController
    }

    // topController should now be your topmost view controller
}

对于Swift 3+:

if var topController = UIApplication.shared.keyWindow?.rootViewController {
    while let presentedViewController = topController.presentedViewController {
        topController = presentedViewController
    }

    // topController should now be your topmost view controller
}

适用于iOS 13+

let keyWindow = UIApplication.shared.windows.filter {$0.isKeyWindow}.first

if var topController = keyWindow?.rootViewController {
    while let presentedViewController = topController.presentedViewController {
        topController = presentedViewController
    }

// topController should now be your topmost view controller
}

extension UIViewController {
    func topMostViewController() -> UIViewController {
        if self.presentedViewController == nil {
            return self
        }
        if let navigation = self.presentedViewController as? UINavigationController {
            return navigation.visibleViewController.topMostViewController()
        }
        if let tab = self.presentedViewController as? UITabBarController {
            if let selectedTab = tab.selectedViewController {
                return selectedTab.topMostViewController()
            }
            return tab.topMostViewController()
        }
        return self.presentedViewController!.topMostViewController()
    }
}

extension UIApplication {
    func topMostViewController() -> UIViewController? {
        return self.keyWindow?.rootViewController?.topMostViewController()
    }
}