如何从递归视图控制器返回根视图控制器(四)

func popToRootViewController(viewController: UIViewController) {
    if let navigationController = viewController.navigationController {
        navigationController.popToRootViewController(animated: true)
    } else if let presentingViewController = viewController.presentingViewController {
        presentingViewController.dismiss(animated: true, completion: nil)
    }
}