从 CloudKit + CoreData 触发多个重复的 NSPersistentStoreRemoteChange 通知

Question

我发现.NSPersistentStoreRemoteChange通知被多次收到，有时多达 10 次。

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我认为这没有害处，但最好的情况是它会耗尽处理能力。

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所以我的问题是：

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• 这有害吗？
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• 我可以阻止它吗？
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• 如果没有，是否有推荐的方法来忽略重复的通知？
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--

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我有以下代码来设置我的容器。它包含在单例的初始化程序中，我已经确认它被调用一次。

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guard let modelURL = Bundle(for: type(of: self)).url(forResource: momdName, withExtension:"momd"),\n            let mom = NSManagedObjectModel(contentsOf: modelURL)\n            else {\n                fatalError(" Error loading model from bundle")\n        }\n        \n        let containerURL = folderToStoreDatabaseIn.appendingPathComponent("Model.sqlite")\n      \n            container = NSPersistentCloudKitContainer(name: momdName, managedObjectModel: mom)\n            \n            guard let description = container.persistentStoreDescriptions.first else {\n                fatalError(" ###\\(#function): Failed to retrieve a persistent store description.")\n            }\n            \n            description.url = containerURL\n            description.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)\n            description.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)\n              \n        super.init()\n        \n            // this must be called after super.init()\n            // ***** ADD OBSERVER *****\n            NotificationCenter.default.addObserver(self,\n                                                   selector: #selector(updatedFromCKCD(_:)),\n                                                   name: .NSPersistentStoreRemoteChange,\n                                                   object: container.persistentStoreCoordinator)\n        \n        if let tokenData = try? Data(contentsOf: tokenFile) {\n            do {\n                lastToken = try NSKeyedUnarchiver.unarchivedObject(ofClass: NSPersistentHistoryToken.self, from: tokenData)\n            } catch {\n                Logger.error(" ###\\(#function): Failed to unarchive NSPersistentHistoryToken. Error = \\(error)")\n            }\n        }\n

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处理这些更改的代码：

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// https://developer.apple.com/documentation/coredata/consuming_relevant_store_changes\n    @objc func updatedFromCKCD(_ notifiction: Notification) {\n        let fetchHistoryRequest = NSPersistentHistoryChangeRequest.fetchHistory(\n            after: lastToken\n        )\n        \n        let context = container.newBackgroundContext()\n        guard\n            let historyResult = try? context.execute(fetchHistoryRequest)\n                as? NSPersistentHistoryResult,\n            let history = historyResult.result as? [NSPersistentHistoryTransaction]\n            else {\n                Logger.error("\xe2\x9b\x88 Could not convert history result to transactions")\n                assertionFailure()\n                return\n        }\n        Logger.debug("\xe2\x9b\x88 Found cloud changes since: \\(self.lastToken?.description ?? "nil")")\n        \n        DispatchQueue.main.async {\n        // look for particular set of changes which require the user to take action\n        ...\n        }\n    }\n

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