具有 privateQueueConcurrencyType 的 NSFetchedResultsController - 更改不调用委托方法

Question

在将 NSFetchedResultsControllerDelegate 设置为 privateQueueConcurrencyType 的 concurrencyType 值时，我无法调用我的 NSFetchedResultsControllerDelegate 方法。

考虑这个例子：

fileprivate lazy var fetchedResultsController: NSFetchedResultsController<Note> = {
    // Initialize Fetch Request
    let fetchRequest: NSFetchRequest<Note> = Note.fetchRequest()

    // Add Sort Descriptors
    let sortDescriptor = NSSortDescriptor(key: "updatedAt", ascending: false)
    fetchRequest.sortDescriptors = [sortDescriptor]

    // Initialize Fetched Results Controller
    let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.coreDataManager.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)

    // Configure Fetched Results Controller
    fetchedResultsController.delegate = self

    return fetchedResultsController
}()

coreDataManager class 有这个：

private(set) lazy var managedObjectContext: NSManagedObjectContext = {
    let managedObjectContext = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)

    managedObjectContext.persistentStoreCoordinator = self.persistentStoreCoordinator

    return managedObjectContext
}()

如果我调用fetchedResultsController.managedObjectContext.delete(note)然后保存，调用controller:didChangeObject:atIndexPath:forChangeType:newIndexPath方法，我可以响应删除笔记对象。

如果我把上面的代码改成：

fileprivate lazy var fetchedResultsController: NSFetchedResultsController<Note> = {
    // Initialize Fetch Request
    let fetchRequest: NSFetchRequest<Note> = Note.fetchRequest()

    // Add Sort Descriptors
    let sortDescriptor = NSSortDescriptor(key: "updatedAt", ascending: false)
    fetchRequest.sortDescriptors = [sortDescriptor]

    let managedObjectContext = NSManagedObjectContext(concurrencyType: .concurrencyType`)

    managedObjectContext.persistentStoreCoordinator = self.coreDataManager.managedObjectContext.persistentStoreCoordinator

    // Initialize Fetched Results Controller
    let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)

    // Configure Fetched Results Controller
    fetchedResultsController.delegate = self

    return fetchedResultsController
}()

它专门将托管对象上下文 'usage' 从使用 self.coreDataManager.managedObjectContext 更改为应该在后台线程上工作的新版本，删除项目时永远不会调用委托方法。

我在 viewDidLoad
这在使用 'main' 托管对象时工作正常，self.coreDataController.managedObjectContext
我或多或少地使用 https://github.com/bartjacobs/ExploringTheFetchedResultsControllerDelegateProtocol 提供的代码来演示这一点 - 正如我上面所说，请调整 fetchedResultsController 方法以使用不同的 NSManagedObjectContext

所以我的主要问题是 - 如何在使用这种类型的 NSManagedObjectContext 时调用 NSFetchedResultsControllerDelegate 方法？

Answer 1

fetchedResultsController 正在监视您刚刚创建的上下文，该上下文未处理更新。如果您希望更改此上下文，则必须为上下文设置 automaticallyMergesChangesFromParent = true。

Answer 2

正如 John 所说，NSFetchedResultsController 仅监控关联的托管上下文，例如

lazy var fetchedResultsController: NSFetchedResultsController = { () -> NSFetchedResultsController<NSFetchRequestResult> in
        let request = NSFetchRequest<NSFetchRequestResult>.init(entityName: "Repository")
        let descriptors = [NSSortDescriptor.init(key: "name", ascending: true), NSSortDescriptor.init(key: "name", ascending: true)]
        request.sortDescriptors = descriptors
        let resultsController = NSFetchedResultsController.init(fetchRequest: request, managedObjectContext: CoreDataManager.shared.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
        
        resultsController.delegate = self
        return resultsController
    }()

从 .privateQueueConcurrencyType 继承你的 .mainQueueConcurrencyType 就像下面的代码

lazy var managedObjectContext: NSManagedObjectContext = {
        let context = NSManagedObjectContext.init(concurrencyType: .mainQueueConcurrencyType)
        context.parent = self.privateQueueManagedObjectContext
        context.automaticallyMergesChangesFromParent = true
        return context
    }()
    
    lazy var privateQueueManagedObjectContext: NSManagedObjectContext = {
        let context = NSManagedObjectContext.init(concurrencyType: .privateQueueConcurrencyType)
        context.persistentStoreCoordinator = self.persistentStoreCoordinator
        return context
    }()

不要忘记在主上下文中添加 context.automaticallyMergesChangesFromParent = true 以通知 privateQue 上下文的后台操作。

我希望这会奏效

具有 privateQueueConcurrencyType 的 NSFetchedResultsController - 更改不调用委托方法

NSFetchedResultsController with privateQueueConcurrencyType - changes do not call delegate methods

core-data

nsfetchedresultscontroller

ios