如何在swift中解除实例化的导航rootviewcontroller

Question

下面是我用来实例化viewController

的工作代码

let myPage = self.storyboard?.instantiateViewControllerWithIdentifier("myViewController") as! myViewController

        let myNav = UINavigationController(rootViewController: myPage)

        let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

        appDelegate.window?.rootViewController = myNav

有人可以提供帮助并提供解除myViewController的解决方案吗？