从非活动状态恢复应用程序后，NSManagedObject 的 managedObjectContext 变为 nil

Question

也许你能帮忙，我在其他问题中找不到类似的东西，所以我想我可能漏掉了一些明显的东西。

我在 Swift 中有 CoreData + iCloud 应用程序。

问题场景：

启动应用程序
NSManagedObject read/update
按 "Home"（使应用程序处于非活动状态）
恢复应用程序
NSManagedObject read/update

如果我已经在我的设备上登录 iCloud，那么这就可以正常工作。

如果我从 iCloud 注销，那么所有应用程序都可以正常工作，就像我执行问题场景一样，然后在第 5 步中 NSManagedObject 的 managedObjectContext 为 nil，因此我无法对其进行任何更改，并且由于丢失上下文，一旦我需要现有对象的上下文，它就会崩溃。

我的问题：

为什么会出现问题场景中的情况？
如何解决此问题，以便如果应用程序已变为非活动状态，然后在 iCloud 用户未登录的情况下处于活动状态，CoreData 会继续工作？

我的 CoreDataStack:

class CoreDataStack: CustomStringConvertible
{
    static let sharedManager = CoreDataStack()
    static let applicationDocumentsDirectoryName = "iCloud.com.myCompany.myAppID"
    static let errorDomain = "CoreDataStack"

    static let modelName = "DB"
    static let storeName = "DB"
    static var storeFileName: String
    {
        return storeName + ".sqlite"
    }
    var options : [String : AnyObject]?

    var inMemory: Bool = false


    var description: String
    {
        var desc = "context: \(self.managedObjectContext)\n" +
            "modelName: \(CoreDataStack.modelName)" +
            "storeURL: \(self.storeURL)"

        desc += "\nPersistent Stores:\n"
        for store in persistentStoreCoordinator.persistentStores
        {
            desc += "* \(store.URL!.absoluteString)"
        }

        return desc
    }


    lazy var managedObjectModel: NSManagedObjectModel =
    {
        let modelURL = NSBundle.mainBundle().URLForResource(modelName, withExtension: "momd")!
        return NSManagedObjectModel(contentsOfURL: modelURL)!
    }()


    lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator =
    {
        let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)

        do
        {
            if self.inMemory
            {
                try coordinator.addPersistentStoreWithType(
                    NSInMemoryStoreType,
                    configuration: nil,
                    URL: nil,
                    options: nil)
            } else
            {
                try coordinator.addPersistentStoreWithType(
                    NSSQLiteStoreType,
                    configuration: nil,
                    URL: self.storeURL,
                    options: self.options)
            }
        } catch var error as NSError
        {
            VTLog.error("Persistent Store Error: \(error)")
        } catch
        {
            fatalError("Error creating Persistent Store!")
        }
        return coordinator
    }()


    /// The directory the application uses to store the Core Data store file.
    lazy var applicationSupportDirectory: NSURL =
    {
        let fileManager = NSFileManager.defaultManager()
        let urls = fileManager.URLsForDirectory(.ApplicationSupportDirectory, inDomains: .UserDomainMask)
        let applicationSupportDirectoryURL = urls.last!
        let applicationSupportDirectory =
            applicationSupportDirectoryURL.URLByAppendingPathComponent(applicationDocumentsDirectoryName)

        do
        {
            let properties = try applicationSupportDirectory.resourceValuesForKeys([NSURLIsDirectoryKey])

            if let isDirectory = properties[NSURLIsDirectoryKey] as? Bool where isDirectory == false
            {
                let description = NSLocalizedString("Could not access the application data folder.",
                                                    comment: "Failed to initialize applicationSupportDirectory.")
                let reason = NSLocalizedString("Found a file in its place.",
                                               comment: "Failed to initialize applicationSupportDirectory.")

                throw NSError(domain: errorDomain, code: 201, userInfo:
                [
                    NSLocalizedDescriptionKey: description,
                    NSLocalizedFailureReasonErrorKey: reason
                ])
            }
        } catch let error as NSError where error.code != NSFileReadNoSuchFileError
        {
            fatalError("Error occured: \(error).")
        } catch
        {
            let path = applicationSupportDirectory.path!

            do
            {
                try fileManager.createDirectoryAtPath(path, withIntermediateDirectories:true, attributes:nil)
            }
            catch
            {
                fatalError("Could not create application documents directory at \(path).")
            }
        }

        return applicationSupportDirectory
    }()


    /// URL for the main Core Data store file.
    lazy var storeURL: NSURL =
    {
        return self.applicationSupportDirectory.URLByAppendingPathComponent(storeFileName)
    }()


    lazy var managedObjectContext: NSManagedObjectContext =
    {
        let context = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
        context.persistentStoreCoordinator = self.persistentStoreCoordinator
        return context
    }()


    // ****************************************
    // MARK: - iCloud Sync
    // ****************************************

    var updateContextWithUbiquitousContentUpdates: Bool = false
    {
        willSet
        {
            ubiquitousChangesObserver = newValue ? NSNotificationCenter.defaultCenter() : nil
        }
    }


    private var ubiquitousChangesObserver: NSNotificationCenter?
    {
        didSet
        {
            oldValue?.removeObserver(
                self,
                name: NSPersistentStoreDidImportUbiquitousContentChangesNotification,
                object: persistentStoreCoordinator)

            ubiquitousChangesObserver?.addObserver(
                self,
                selector: #selector(self.persistentStoreDidImportUbiquitousContentChanges(_:)),
                name: NSPersistentStoreDidImportUbiquitousContentChangesNotification,
                object: persistentStoreCoordinator)


            oldValue?.removeObserver(
                self,
                name: NSPersistentStoreCoordinatorStoresWillChangeNotification,
                object: persistentStoreCoordinator)

            ubiquitousChangesObserver?.addObserver(
                self,
                selector: #selector(self.persistentStoreCoordinatorWillChangeStores(_:)),
                name: NSPersistentStoreCoordinatorStoresWillChangeNotification,
                object: persistentStoreCoordinator)
        }
    }


    @objc func persistentStoreDidImportUbiquitousContentChanges(notification: NSNotification)
    {
        VTLog.debug("Merging ubiquitous content changes")
        VTLog.debug(notification)

        self.managedObjectContext.performBlock
        {
            self.managedObjectContext.mergeChangesFromContextDidSaveNotification(notification)
        }
    }


    @objc func persistentStoreCoordinatorWillChangeStores(notification: NSNotification)
    {
        VTLog.debug(notification)

        if managedObjectContext.hasChanges
        {
            do
            {
                try managedObjectContext.save()
            } catch let error as NSError
            {
                print("Error saving: \(error)", terminator: "")
            }
        }
        managedObjectContext.reset()
    }


    // ***********************************************
    // * Data: iCloud Container Actions
    // ***********************************************

    func deleteiCloudContainer()
    {
        VTLog.debug("Deleting iCloud Container...")

        let currentStore = managedObjectContext.persistentStoreCoordinator!.persistentStores.last!

        VTLog.debug("Located data store [\(currentStore)]")

        managedObjectContext.reset()
        VTLog.debug("managedObjectContext.reset() - OK")

        do
        {
            try managedObjectContext.persistentStoreCoordinator?.removePersistentStore(currentStore)
            VTLog.debug("removePersistentStore() - OK")
        } catch let error as NSError
        {
            VTLog.error("Could not remove persistent store [\(currentStore)]: \(error)")
        }

        do
        {
            try NSPersistentStoreCoordinator.removeUbiquitousContentAndPersistentStoreAtURL(
                currentStore.URL!, options: currentStore.options)
            VTLog.debug("removeUbiquitousContentAndPersistentStoreAtURL() - OK")
        } catch let error as NSError
        {
            VTLog.error("Could not remove Ubiquitous Content and Persistent Store at URL [\(currentStore)]: \(error)")
        }
    }


    //*******************************************
    // MARK: - Init
    //*******************************************

    init(inMemory:Bool = false)
    {
        self.inMemory = inMemory

        self.options = [NSMigratePersistentStoresAutomaticallyOption: true,
            NSInferMappingModelAutomaticallyOption: true,
            NSPersistentStoreUbiquitousContentNameKey: CoreDataStack.storeName]
    }

}

可能有帮助的其他信息：

所有这些都在模拟器上，无论版本如何：iOS 9.2，iOS 9.3。
当我登录到 iCloud 后，一切正常。
我注意到 DB.sqlite 文件实际上不存在于路径 storeURL 上，它是在路径上创建的，如下所示，但无论是否登录 iCloud 都一样，所以我不知道是否应该是这样的。
当我恢复应用程序时，我看到以下操作序列：

@ 2016-04-12 11:30:36: AppDelegate: applicationDidEnterBackground:133: (thread): {number = 10, name = main}

@ 2016-04-12 11:30:37: AppDelegate: applicationWillEnterForeground:141: (thread): {number = 11, name = main}

2016-04-12 11:30:37.150 Count Myself[57886:19968276] -PFUbiquitySwitchboardEntryMetadata setUseLocalStorage:: CoreData: Ubiquity: nobody~sim7CC36E42-82CB-5152-91BE-4DD26FE0A420:DB Using local storage: 1 for new NSFileManager current token (null)

@ 2016-04-12 11:30:37: CoreDataStack: persistentStoreCoordinatorWillChangeStores:203: NSConcreteNotification 0x7fd3e8d8fdc0 {name = NSPersistentStoreCoordinatorStoresWillChangeNotification; object = ; userInfo = { NSPersistentStoreUbiquitousTransitionTypeKey = 2; added = ( " (URL: file:///Users/maris/Library/Developer/CoreSimulator/Devices/F9A852DA-595C-4DE2-ADD7-7DECD7D814AD/data/Containers/Data/Application/107B6DB1-C4DC-4626-8933-DACD0575F184/Library/Application%20Support/iCloud.com.myCompany.myAppID/CoreDataUbiquitySupport/nobody~sim7CC36E42-82CB-5152-91BE-4DD26FE0A420/DB/local/store/DB.sqlite)" ); removed = ( " (URL: file:///Users/maris/Library/Developer/CoreSimulator/Devices/F9A852DA-595C-4DE2-ADD7-7DECD7D814AD/data/Containers/Data/Application/107B6DB1-C4DC-4626-8933-DACD0575F184/Library/Application%20Support/iCloud.com.myCompany.myAppID/CoreDataUbiquitySupport/nobody~sim7CC36E42-82CB-5152-91BE-4DD26FE0A420/DB/local/store/DB.sqlite)" ); }} (thread): {number = 12, name = main}

@ 2016-04-12 11:30:37: AppDelegate: applicationDidBecomeActive:152: context: modelName: DBstoreURL: file:///Users/maris/Library/Developer/CoreSimulator/Devices/F9A852DA-595C-4DE2-ADD7-7DECD7D814AD/data/Containers/Data/Application/107B6DB1-C4DC-4626-8933-DACD0575F184/Library/Application%20Support/iCloud.com.myCompany.myAppID/DB.sqlite Persistent Stores: * file:///Users/maris/Library/Developer/CoreSimulator/Devices/F9A852DA-595C-4DE2-ADD7-7DECD7D814AD/data/Containers/Data/Application/436959B5-7850-4156-AB3D-A11BE72FF1AF/Library/Application%20Support/iCloud.com.myCompany.myAppID/CoreDataUbiquitySupport/nobody~sim7CC36E42-82CB-5152-91BE-4DD26FE0A420/DB/local/store/DB.sqlite

我这样设置的时候出现的问题： stack.updateContextWithUbiquitousContentUpdates = true 但是，如果我不将其设置为 true，我想我不会立即从 iCloud 获取更新。
查看 GitHub 演示问题的 Xcode 项目：https://github.com/marisveide/iCloudCoreDataProblem（阅读顶部的 AppDelegate.swift 文件注释）如果看到单独分支中的代码更改解决方案不会丢失上下文，那就太好了。

Answer 1

当您退出并重新启动时，应用程序将从内存中删除，因此会再次创建持久存储和上下文，并且它们 link 在一起。

当您将其置于背景中然后提出未发生的情况时，商店和上下文仍然存在。看起来这里发生的是持久存储文件被更改并且上下文与其断开连接（这是一个猜测，我没有测试过）。

所以，看起来 persistentStoreCoordinatorWillChangeStores 你真的应该破坏上下文并创建一个新的上下文。这也意味着销毁所有来自旧上下文的托管对象并从新上下文获取新版本（假设它们仍然存在）。

Answer 2

好的，我找到了解决方案 - 也许这对其他人也有帮助。

基本上，通过检查 iCloud 是否启用，然后定制 CoreDataStack 设置。

像这样：

init(inMemory:Bool = false)
{
    self.inMemory = inMemory

    self.options = [NSMigratePersistentStoresAutomaticallyOption: true,
                    NSInferMappingModelAutomaticallyOption: true]

    if iCloudEnabled
    {
        self.options?[NSPersistentStoreUbiquitousContentNameKey] = CoreDataStack.storeName
        self.monitorUbiquitousContentUpdatesIfiCloudEnabled()
    }

}

可以在 GitHub 项目示例中找到更多详细信息 - 提交的差异解决了我的问题： https://github.com/marisveide/iCloudCoreDataProblem/commit/1d2da6c000bee7a66274192da2a637ba7c8cabf5#diff-8efc4cba62b5f1efad252e6f27b5b30b

整个项目在这里下载： https://github.com/marisveide/iCloudCoreDataProblem

哇...过去 3 天的调试和搜索 "fun"。

从非活动状态恢复应用程序后，NSManagedObject 的 managedObjectContext 变为 nil

managedObjectContext for NSManagedObject becomes nil after restoring app from inactive

core-data

nsmanagedobjectcontext

ios

icloud

swift