斯威夫特。使用Coredata预览＆＃x2013;人口，单身和怪异的行为

Question

我有一个小型应用程序，可以将任意事件添加到Coredata。 而且我正在努力准备预览数据。

正确的行为

在预览窗口中，我看到一个带有内容“测试事件”的文本

struct ContentView_Previews: PreviewProvider {
static var previews: some View {
       
        //init coredata
        let container = NSPersistentContainer(name: "Model")
        container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
        container.loadPersistentStores() { description, error in
            if let error = error {
                print("Can't load core data \(error.localizedDescription)")
            }
        }

        //adding event
        let event = Event(context: container.viewContext)
        event.id = UUID()
        event.name = "Test"
        try! container.viewContext.save()
        
        //getting events
        let request = Event.fetchRequest()
        let events = try! container.viewContext.fetch(request)
        
        //view
        return VStack {
            ForEach(events, id: \.id) { event in
                Text("\(event.id?.uuidString ?? "") \(event.name ?? "") fs")
            }
        }
}

，但是如果我尝试将逻辑移至datacontroller，我会得到7个具有相同的文本块名称，但是不同的uuids

class DataController {
    
    static let preview = DataController()
    
    private(set) var container: NSPersistentContainer
    
    private init(inMemory: Bool = false) {
        
        self.container = NSPersistentContainer(name: "Model")
        container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")       
        
        
        container.loadPersistentStores() { description, error in
            if let error = error {
                fatalError("Can't load core data \(error.localizedDescription)")
            }
        }    
    }
}



struct ContentView_Previews: PreviewProvider {
    
    static let dataController = DataController.preview
    
    static var previews: some View {

        //adding event
        let event = Event(context: dataController.container.viewContext)
        event.id = UUID()
        event.name = "Test event"
        try! dataController.container.viewContext.save()
        
        //getting events
        let request = Event.fetchRequest()
        let events = try! dataController.container.viewContext.fetch(request)
        
        //view
        return VStack {
            ForEach(events, id: \.id) { event in
                Text("\(event.id?.uuidString ?? "") \(event.name ?? "")")
            }
        }
   }
}

是什么可能导致此类行为？

模型是手动生成的。我更改的唯一一件事 - 评论@Objc（event），因为使用此语句的预览根本不起作用。