swift返回当前控制器

func getCurrentViewController(with rootViewController: UIViewController!)->UIViewController?{
        if nil == rootViewController{
            return nil
        }
        // UITabBarController就接着查找它当前显示的selectedViewController
        if rootViewController.isKind(of: UITabBarController.self){
            return self.getCurrentViewController(with: (rootViewController as! UITabBarController).selectedViewController)
            // UINavigationController就接着查找它当前显示的visibleViewController
        }else if rootViewController.isKind(of: UINavigationController.self){
            return self.getCurrentViewController(with: (rootViewController as! UINavigationController).visibleViewController)
            // 如果当前窗口有presentedViewController,就接着查找它的presentedViewController
        }else if nil != rootViewController.presentedViewController{
            return self.getCurrentViewController(with: rootViewController.presentedViewController)
        }
        // 否则就代表找到了当前显示的控制器
        return rootViewController
    }

//调用方式
let rootVC = UIApplication.shared.keyWindow?.rootViewController
let currentVC = getCurrentViewController(with: rootVC)