NSFetchedResultsController将重复的部分添加到UICollectionView

Question

我有NSFetchedResultsController从CoreData获取对象并更新UICollectionView以相应地显示数据。 UICollectionView中的数据根据​​CoreData关系中的属性按部分组织。这种关系如下所示

// an Item belongs to exactly one Category - a Category can host multiple Items
Item <<---> Category

我添加了一个新的Item，其中Category已经存在于数据库中，新的部分会添加到UICollectionView，但这仅适用于第一个新的Item - 稍后添加的每个新Item都会插入此新部分。新部分未显示在sqlite数据库中，只显示在由UICollectionView管理的NSFetchedResultsController中。

我使用以下代码插入新项目

let newItem = Item(context: managedObjectContext)
...
let request: NSFetchRequest<Category> = Category.fetchRequest()
request.predicate = NSPredicate(format: "name = %@", "categoryA")

do {
    let searchResults = try managedObjectContext.fetch(request)
    newItem.category = searchResults.first  
} catch {
    print("Error with request: \(error)")
}

关闭应用并重新启动它后，新版块会消失，所有Items都位于正确的部分 - NSFetchedResultsController可能有问题，所以这是重要的代码。< / p>

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) {
    if type == NSFetchedResultsChangeType.insert {
        blockOperations.append(
            BlockOperation(block: { [weak self] in
                if let this = self {
                    this.collectionView!.insertSections(NSIndexSet(index: sectionIndex) as IndexSet)

                }
                })
        )
    }
    else if type == NSFetchedResultsChangeType.update {
        blockOperations.append(
            BlockOperation(block: { [weak self] in
                if let this = self {
                    this.collectionView!.reloadSections(NSIndexSet(index: sectionIndex) as IndexSet)
                }

                })
        )
    }
    else if type == NSFetchedResultsChangeType.delete {
        blockOperations.append(
            BlockOperation(block: { [weak self] in
                if let this = self {
                    this.collectionView!.deleteSections(NSIndexSet(index: sectionIndex) as IndexSet)
                } 
                })
        )
    }
}

以下是在UICollectionView添加新Item后CoreData的图片

修改

我使用此代码实例化NSFetchedResultsController

    var _fetchedResultsController: NSFetchedResultsController<Item>? = nil

var fetchedResultController: NSFetchedResultsController<Item> {
    if _fetchedResultsController != nil {
        return _fetchedResultsController!
    }

    let fetchRequest: NSFetchRequest<Item> = Item.fetchRequest()
    let managedObjectContext = CoreDataStack.sharedInstance.getContext()

    fetchRequest.predicate = NSPredicate(format: "completed != true")

    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "category", ascending: true)]
    let resultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managedObjectContext, sectionNameKeyPath:"category", cacheName: nil)

    resultsController.delegate = self;
    _fetchedResultsController = resultsController

    do {
        try _fetchedResultsController!.performFetch()
    } catch {
        let nserror = error as NSError
        fatalError("Unresolved error \(nserror)")
    }
    return _fetchedResultsController!
}