SwiftUI预览画布和核心数据

import SwiftUI
import CoreData

struct ContentView: View {
    @Environment(\.managedObjectContext) var context
    @FetchRequest(sortDescriptors: []) var items: FetchedResults<Item>

    var body: some View {
        List(items, id: \.id) { item in
            Text(item.name ?? "Unknown")
        }
        .onAppear(perform: loadData)
    }

    func loadData() {
        let request: NSFetchRequest<Item> = Item.fetchRequest()
        do {
            items = try context.fetch(request)
        } catch {
            print("Failed to fetch items: \(error)")
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView().environment(\.managedObjectContext, PersistenceController.preview.container)
    }
}

class PersistenceController {
    static var preview: PersistenceController = {
        let controller = PersistenceController()

        do {
            try controller.container.viewContext.save()
        } catch {
            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
        return controller
    }()

    let container = NSPersistentContainer(name: "ItemModel")

    init() {
        container.loadPersistentStores { (storeDescription, error) in
            if let error = error as NSError? {
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        }
    }
}