swift - 如何为该SwiftUI核心数据模型正确插入排序描述符？

我正在尝试实现如下所述的MVVM体系结构:
https://medium.com/better-programming/swiftui-and-coredata-the-mvvm-way-ab9847cbff0f
但是我在此文件中遇到运行时错误，无法弄清楚在何处添加排序描述符:

import Foundation
import CoreData
import Combine
import UIKit

class ItemsStorage: NSObject, ObservableObject {
    var items = CurrentValueSubject<[Item], Never>([])
    private let itemFetchController: NSFetchedResultsController<Item>

    //SINGLETON INSTANCE
    static let shared: ItemsStorage = ItemsStorage()  ///Run time error: Thread 1: "An instance of NSFetchedResultsController requires a fetch request with sort descriptors"

    private override init() {

        /// This line doesn't solve the issue
        let sort = NSSortDescriptor(key: "name_", ascending: true)

        itemFetchController = NSFetchedResultsController(

        fetchRequest: Item.fetchRequest(),
        managedObjectContext: PersistenceController.shared.container.viewContext,
        sectionNameKeyPath: nil, cacheName: nil
        )

        /// This line doesn't solve the issue
        itemFetchController.fetchRequest.sortDescriptors = [sort]

        super.init()

        itemFetchController.delegate = self

        do {
            try itemFetchController.performFetch()
            items.value = itemFetchController.fetchedObjects ?? []
        } catch {
            NSLog("Error: could not fetch objects")
        }
    }

    func add(){

    }

    func update(withID id: UUID) {

    }

    func delete(id: UUID) {

    }
}

extension ItemsStorage: NSFetchedResultsControllerDelegate  {
    public func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        guard let items = controller.fetchedObjects as? [Item] else { return }
        NSLog("Context has changed, reloading items ...")
        self.items.value = items
    }
}

最佳答案

在初始化提取的结果 Controller 之前，您需要为fetchRequest设置排序描述符:

    let sort = NSSortDescriptor(key: "name_", ascending: true)
    let itemFetchRequest = Item.fetchRequest()
    itemFetchRequest.sortDescriptors = [sort]

    itemFetchController = NSFetchedResultsController(

    fetchRequest: itemFetchRequest,
    managedObjectContext: PersistenceController.shared.container.viewContext,
    sectionNameKeyPath: nil, cacheName: nil
    )

关于swift - 如何为该SwiftUI核心数据模型正确插入排序描述符？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/66081123/