iOS 8:通过订阅获得CKRecord更改的通知

Question

我正在运行一个CKFetchNotificationChangesOperation来下载所有的更新通知，这些通知应该是从我的应用程序上次运行以来发送的。

正如我所期望的，我得到了一堆CKNotification对象，但是每个CKNotification的recordFields对象都是空的。我希望它会填充我的对象的所有更改的属性。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，而我的对象有比3个值多得多的值可以更新。

所以现在我想，我只需要获取CKNotification对象，看看它是否是更新，然后重新获取它所指向的对象来检索它的数据。然后，我可以对新的CKRecord和旧的进行比较，看看有什么变化。

我的理解正确吗？

Answer 1

首先，您需要存储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的下一个调用中传递它。则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重新获取这些ID的所有CKRecord，并相应地更新模型对象。

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)
}

Answer 2

iOS 11中弃用了CKFetchNotificationChangesOperation，在标题中苹果建议：

使用CKDatabaseSubscription、CKFetchDatabaseChangesOperation和CKFetchRecordZoneChangesOperation，而不是通过迭代通知来枚举已更改的记录区