@environmentkey的核心数据结果

Question

我尝试从如何重新使用相同的fetchrequest，而不是在几个视图中使用相同的请求？

我在@main中构建了带有核心数据的简单应用程序，

//  Count+CoreDataProperties.swift

extension Count {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Count> {
        return NSFetchRequest<Count>(entityName: "Count")
    }

    @NSManaged public var id: UUID?
    @NSManaged public var name: String?
    @NSManaged public var number: Int16

}

    //  CoreDataManager.swift // all structs to fetch core data and set Environment
  
    public struct CountEnvironmentKey: EnvironmentKey {
        public static var defaultValue: [Count] = []
    }
    
    public extension EnvironmentValues {
        var counts: [Count] {
            get { self[CountEnvironmentKey.self] }
            set { self[CountEnvironmentKey.self] = newValue }
        }
    }
    
    public extension View {
        func setCount(_ counts: [Count]) -> some View {
            environment(\.counts,  counts)
        }
    }
    
    struct CountLoaderViewModifier: ViewModifier {
        @FetchRequest( sortDescriptors: [])
        var counts: FetchedResults<Count>
        
        func body(content: Content) -> some View {
            content
                .setCount(Array(counts))
        }
    }
    
    extension View {
        func loadCounts() -> some View {
            modifier(CountLoaderViewModifier())
        }
    }


//  ContentView.swift


struct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext
    @Environment(\.counts) var counts

    var body: some View {
        NavigationView {
            List {
                ForEach(counts) { item in
                    NavigationLink {
                        Text("\(item.number)")
                    } label: {
                        Text("Item at \(item.name!)")
                    }
                }
                .onDelete(perform: deleteItems)
            }
            .toolbar {
                ToolbarItem(placement: .navigationBarTrailing) {
                    EditButton()
                }
                ToolbarItem {
                    Button(action: addItem) {
                        Label("Add Item", systemImage: "plus")
                    }
                }
            }
            Text("Select an item")
        }

    }

    private func addItem() {
        withAnimation {
            let newItem = Count(context: viewContext)
            newItem.name = "Name"
            newItem.number = 1
            newItem.id = UUID()

            do {
                try viewContext.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                let nsError = error as NSError
                fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
            }
        }
    }

    private func deleteItems(offsets: IndexSet) {
        withAnimation {
            offsets.map { counts[$0] }.forEach(viewContext.delete)

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

//  MyEnvApp.swift


@main
struct MyEnvApp: App {
    
    let persistenceController = PersistenceController.shared


    var body: some Scene {
        WindowGroup {
            ContentView()
                .environment(\.managedObjectContext, persistenceController.container.viewContext)
               .loadCounts()
        }
    }
}


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

我会收到警告 环境中的上下文未连接到持久的商店协调器：＆lt; nsmanagedObjectContext：0x60000273dfb0＆gt; 样本中的代码 @ObseverObject var persistenceManager = persistenceManager（usage：.main） 还会产生错误，我知道我需要将核心数据存储连接到环境，

感谢提前的帮助

Answer 1

.loadCounts（）被用作外部（之后）的修饰符，该修饰符设置了环境中的托管对象上下文。这意味着环境价值不存在于您的修饰符体内。尝试移动.loadCounts（）上面的.environment（\。托管ObjectContext，...）。