我正在尝试清理我的代码并创建和扩展UIViewController以注册和取消注册我的键盘。在我的实用程序文件中，我有以下内容:extensionUIViewController{//RegisterthekeyboardfornotificationsinviewDidLoadfuncregisterForKeyboardNotifications(){//AddingnotifiesonkeyboardappearingNSNotificationCenter.defaultCenter().addObserver(self,selector:#selector(CreateEve