swift - 如何为UIDocument添加通知观察者？

Question

private var documentObserver: NSObjectProtocol?

override func viewDidLoad() {
super.viewDidLoad()

documentObserver  = NotificationCenter.default.addObserver(
            forName: Notification.Name.UIDocumentStateChangedNotification ,
            object: document,
            queue: OperationQueue.main,
            using: { notification in
                print("docuemntState Changed to \(self.document!.documentState)")
            }
        )

}

我正在尝试这样做，但 Xcode 显示了一个错误:

Type 'Notification.Name' (aka 'NSNotification.Name') has no member 'UIDocumentStateChangedNotification '

Answer 1

您要查找的通知名称是UIDocument的静态常量

UIDocument.stateChangedNotification