How to find visible view controller?

    func topMostController() -> UIViewController {
        var topController = UIApplication.shared.keyWindow?.rootViewController
        while (topController?.presentedViewController != nil) {
            topController = topController?.presentedViewController
        }
        return topController!
    }
    
    func topViewController(_ controller: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
        if let navigationController = controller as? UINavigationController {
            return topViewController(navigationController.visibleViewController)
        }
        if let tabController = controller as? UITabBarController {
            if let selected = tabController.selectedViewController {
                return topViewController(selected)
            }
        }
        if let presented = controller?.presentedViewController {
            return topViewController(presented)
        }
        return controller
    }