如何同时关闭两个模式视图控制器？

 ```swift

 protocol SecondViewControllerDelegate: class {

     func dismissSecondViewController()

 }

 class SecondViewController: UIViewController {

     weak var delegate: SecondViewControllerDelegate?

     // ...

 }

 ```

 ```swift

 delegate?.dismissSecondViewController()

 ```

 ```swift

 class FirstViewController: UIViewController, SecondViewControllerDelegate {

     // ...

     func dismissSecondViewController() {

         dismiss(animated: true, completion: nil) // 关闭第二个模态视图控制器

         dismiss(animated: true, completion: nil) // 关闭第一个模态视图控制器

     }

 }

 ```

 ```swift

 NotificationCenter.default.post(name: NSNotification.Name("DismissModalViewControllers"), object: nil)

 ```

 ```swift

 class FirstViewController: UIViewController {

     override func viewDidLoad() {

         super.viewDidLoad()

         NotificationCenter.default.addObserver(self, selector: #selector(dismissModalViewControllers), name: NSNotification.Name("DismissModalViewControllers"), object: nil)

     }

     @objc func dismissModalViewControllers() {

         dismiss(animated: true, completion: nil) // 关闭第二个模态视图控制器

         dismiss(animated: true, completion: nil) // 关闭第一个模态视图控制器

     }

 }

 ```