NSSelectorFromString和Selector结构

我有一个问题,NSSelectorFromString和Selector有什么不同 如果我使用选择器创建选择器

 let bSelector = Selector("registerRemoteNotificationWithApplication:")
 let cSelector = Selector(stringLiteral: "registerRemoteNotificationWithApplication:")

我收到警告

当使用NSSelectorFromString时

 let aSelector = NSSelectorFromString("registerRemoteNotificationWithApplication:")

即使函数是用/不用@objc声明的

  @objc func registerRemoteNotification(application:UIApplication) {


}