CoreData 和 SwiftUI:环境中的上下文未连接到持久存储协调器 [英] CoreData and SwiftUI: Context in environment is not connected to a persistent store coordinator

问题描述

我正在尝试通过构建作业管理应用来自学 Core Data.我的代码构建良好，应用程序运行正常，直到我尝试向列表添加新分配.我在以下行中收到此错误 Thread 1: EXC_BREAKPOINT (code=1, subcode=0x1c25719e8):ForEach(courses, id: .self) { course in.控制台也有这个错误:Context in environment is not connected to an persistent store coordinator: <NSManagedObjectContext: 0x2823cb3a0>.

I am trying to teach myself Core Data by building a homework managing app. My code builds fine and the app runs okay until I try to add a new assignment to the list. I get this error Thread 1: EXC_BREAKPOINT (code=1, subcode=0x1c25719e8) on the following line: ForEach(courses, id: .self) { course in. The console also has this error: Context in environment is not connected to a persistent store coordinator: <NSManagedObjectContext: 0x2823cb3a0>.

我对 Core Data 知之甚少，不知道可能是什么问题.我在数据模型中设置了作业"和课程"实体，其中课程与作业具有一对多关系.每项作业都将归入特定课程.

I know very little about Core Data and am at a loss as to what the issue might be. I have set up "Assignment" and "Course" entities in the data model, where Course has a one-to-many relationship to Assignment. Each assignment will be categorized under a particular course.

这是向列表添加新分配的视图的代码:

This is the code for the view that adds a new assignment to the list:

    struct NewAssignmentView: View {

    @Environment(.presentationMode) var presentationMode
    @Environment(.managedObjectContext) var moc
    @FetchRequest(entity: Course.entity(), sortDescriptors: []) var courses: FetchedResults<Course>

    @State var name = ""
    @State var hasDueDate = false
    @State var dueDate = Date()
    @State var course = Course()

    var body: some View {
        NavigationView {
            Form {
                TextField("Assignment Name", text: $name)
                Section {
                    Picker("Course", selection: $course) {
                        ForEach(courses, id: .self) { course in
                            Text("(course.name ?? "")").foregroundColor(course.color)
                        }
                    }
                }
                Section {
                    Toggle(isOn: $hasDueDate.animation()) {
                        Text("Due Date")
                    }
                    if hasDueDate {
                        DatePicker(selection: $dueDate, displayedComponents: .date, label: { Text("Set Date:") })
                    }
                }
            }
            .navigationBarTitle("New Assignment", displayMode: .inline)
            .navigationBarItems(leading: Button(action: {
                self.presentationMode.wrappedValue.dismiss()
            }, label: { Text("Cancel") }),
                                trailing: Button(action: {
                                    let newAssignment = Assignment(context: self.moc)
                                    newAssignment.name = self.name
                                    newAssignment.hasDueDate = self.hasDueDate
                                    newAssignment.dueDate = self.dueDate
                                    newAssignment.statusString = Status.incomplete.rawValue
                                    newAssignment.course = self.course
                                    self.presentationMode.wrappedValue.dismiss()
                                }, label: { Text("Add").bold() }))
        }
    }
}

这是 AppDelegate 中设置持久容器的代码:

Here is the code in AppDelegate that sets up the persistent container:

lazy var persistentContainer: NSPersistentCloudKitContainer = {
    let container = NSPersistentCloudKitContainer(name: "test")
    container.loadPersistentStores(completionHandler: { (storeDescription, error) in
        if let error = error as NSError? {
            fatalError("Unresolved error (error), (error.userInfo)")
        }
    })
    return container
}()

SceneDelegate 中设置环境的代码:

And the code in SceneDelegate that sets up the environment:

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
    // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
    // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).

    // Get the managed object context from the shared persistent container.
    let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

    // Create the SwiftUI view and set the context as the value for the managedObjectContext environment keyPath.
    // Add `@Environment(.managedObjectContext)` in the views that will need the context.
    let contentView = ContentView().environment(.managedObjectContext, context)

    // Use a UIHostingController as window root view controller.
    if let windowScene = scene as? UIWindowScene {
        let window = UIWindow(windowScene: windowScene)
        window.rootViewController = UIHostingController(rootView: contentView)
        self.window = window
        window.makeKeyAndVisible()
    }
}

推荐答案

像您的 moc 这样的环境值只会自动传递给层次结构中的其他视图.因此，如果您显示工作表或任何不属于您的视图层次结构的内容，您将失去环境并且您需要将 moc 传递给新的层次结构，就像您对 ContentView 所做的那样.检查此代码片段:

Environment values like your moc are automatically passed only to other views in the hierarchy. So if you show a sheet or anything that is not part of your view hierarchy you'll lose the environment and you will need to pass the moc to the new hierarchy, like you did for ContentView. Check this code snippet:

.sheet(isPresented: self.$showSheet) {
            SheetView()
                .environment(.managedObjectContext, self.moc)
        }

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