未收到NSWorkspace通知

Question

当我切换应用程序时，我的函数没有被执行：

public class ItemObserver: NSObject {

  @objc public func recievedNotification(notification: NSNotification) {
    print(notification.name)
    print("s")
  }
}

let observer = ItemObserver()

NSWorkspace.shared().notificationCenter.addObserver(observer, selector: #selector(ItemObserver.recievedNotification(notification:)), name: .NSWorkspaceDidActivateApplication, object: nil)