如何正确插入此SwiftUI CoreData模型的排序描述符?
我正在尝试实现如下所述的MVVM体系结构: 但我在该文件中遇到运行时错误,无法确定在何处添加排序描述符:如何正确插入此SwiftUI CoreData模型的排序描述符?,swift,core-data,mvvm,swiftui,nsfetchrequest,Swift,Core Data,Mvvm,Swiftui,Nsfetchrequest,我正在尝试实现如下所述的MVVM体系结构: 但我在该文件中遇到运行时错误,无法确定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 itemFet
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
}
}
<代码>导入基础
导入CoreData
进口联合收割机
导入UIKit
类项存储:NSObject,observeObject{
var items=CurrentValueSubject([])
私有let itemFetchController:NSFetchedResultsController
//单例实例
静态let shared:ItemsStorage=ItemsStorage()///运行时错误:线程1:“NSFetchedResultsController的实例需要具有排序描述符的获取请求”
私有重写init(){
///这句话不能解决问题
让sort=NSSortDescriptor(键:“名称”,升序:true)
itemFetchController=NSFetchedResultsController(
fetchRequest:Item.fetchRequest(),
managedObjectContext:PersistenceController.shared.container.viewContext,
sectionNameKeyPath:nil,cacheName:nil
)
///这句话不能解决问题
itemFetchController.fetchRequest.sortDescriptors=[sort]
super.init()
itemFetchController.delegate=self
做{
请尝试itemFetchController.performFetch()
items.value=itemFetchController.FetchedObject???[]
}抓住{
NSLog(“错误:无法获取对象”)
}
}
func add(){
}
func更新(id:UUID){
}
func delete(id:UUID){
}
}
扩展项存储:NSFetchedResultsControllerDelegate{
公共函数控制器IDChangeContent(\uController:NSFetchedResultsController){
guard let items=controller.fetchedObjects as?[Item]else{return}
NSLog(“上下文已更改,正在重新加载项…”)
self.items.value=项目
}
}
在初始化“获取结果”控制器之前,您需要为“获取请求”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
)
谢谢但是,我在'let itemFetchRequest=Item.fetchRequest()'行中遇到了一个错误。它说“fetchRequest()的用法不明确”,但在我的Item+Helper.swift文件中,我确实有定义fetchRequest的扩展名,如下所示:
extension Item{static func fetchRequest(upredicate:NSPredicate)->NSFetchRequest{let request=NSFetchRequest(entityName:“Item”)return request}
我还有什么问题吗?好的,再看一看,发现这个问题:它似乎解决了后一个问题。现在我有了这个:let sort=NSSortDescriptor(键:“name”,升序:true)let itemFetchRequest:NSFetchRequest=Item.fetchRequest()itemFetchRequest.sortDescriptors=[sort]itemFetchController=NSFetchedResultsController(…