swift - iOS 8 : being notified of CKRecord changes via subscriptions

Question

我正在运行 CKFetchNotificationChangesOperation 来提取自上次我的应用程序运行以来应该发送的所有更新通知。

正如我所料，我得到了一堆 CKNotification 对象，但是这些 CKNotification 中的每一个的 recordFields 对象都是 nil。我希望它会填充我的对象的所有已更改属性。但也许事实并非如此。

我没有指定 CKSubscription 对象的 desiredKeys 属性，这显然会强制 CKNotification recordFields 保存该数据。但是文档说 desiredKeys 只能有 3 个值，而我的对象有超过 3 个可以更新的值。

所以现在我在想，我只需要获取 CKNotification 对象，看看它是否是一个更新，然后重新获取它指向的对象以检索它的数据。然后我可以对新的 CKRecord 与旧的进行比较，看看有什么变化。

我理解正确吗？

Answer 1

首先你需要存储CKFetchNotificationChangesOperation提供的CKServerChangeToken

var notificationChangesOperation = CKFetchNotificationChangesOperation(previousServerChangeToken: previousChangeToken)

var fetchedRecordIDs:[CKRecordID]()

//we just care about inserts, we don't care about of changes of records existing in database, that's why it's enough just to save recordIDs
notificationChangesOperation.notificationChangedBlock = {notification in

    let queryNotif = notification as CKQueryNotification
    //            println("fetched  CKQueryNotification \(queryNotif)")

    if (!contains(fetchedRecordIDs, queryNotif.recordID)) {
        fetchedRecordIDs.append(queryNotif.recordID)
    }
}

notificationChangesOperation.fetchNotificationChangesCompletionBlock = {serverChangeToken, error in
    if (error) {
        println("failed to fetch notification \(error)")
    }

    self.previousChangeToken = serverChangeToken

    completionHandler(recordIDs: fetchedRecordIDs, error: error)
}

container.addOperation(notificationChangesOperation)

var previousChangeToken:CKServerChangeToken? {
    get {
        let encodedObjectData = NSUserDefaults.standardUserDefaults().objectForKey(SubscriptionKeys.PreviousChangeToken) as? NSData

        if (encodedObjectData) {
            return NSKeyedUnarchiver.unarchiveObjectWithData(encodedObjectData) as? CKServerChangeToken
        }

        return nil
    }
    set(newToken) {
        if (newToken) {
            println("new token \(newToken)")

            NSUserDefaults.standardUserDefaults().setObject(NSKeyedArchiver.archivedDataWithRootObject(newToken), forKey:SubscriptionKeys.PreviousChangeToken)
        }
    }
}

然后在 CKFetchNotificationChangesOperation 的下一次调用中传递它。然后此操作将为您提供自上次请求以来的更新。 CKNotification (CKQueryNotification) 为您提供CKRecordID 对象，而不是CKRecord。

因此，您需要使用 CKFetchRecordsOperation 为这些 ID 重新获取所有 CKRecord，并相应地更新您的模型对象。

func queryMessagesWithIDs(IDs:[CKRecordID], completionHandler: ([CKRecord]!, NSError!) -> Void) {
    var fetchRecordsOperation = CKFetchRecordsOperation(recordIDs: IDs)

    var messages:[CKRecord]()

    fetchRecordsOperation.perRecordCompletionBlock = {record, recordID, error in
        if (!error) {
            messages.append(record)
        } else {
            println("failed to get message with ID \(recordID.recordName)")
        }
    }

    fetchRecordsOperation.fetchRecordsCompletionBlock = {_, error in
        if (error) {
            println(error)
        } else {
            messages.sort{$0.creationDate.compare($1.creationDate) == NSComparisonResult.OrderedAscending}
        }

        dispatch_async(dispatch_get_main_queue(), {completionHandler(messages, error)})
    }

    publicDatabase.addOperation(fetchRecordsOperation)
}