SwiftUI @FetchRequest在子视图中崩溃

Question

我在MacOS应用程序（无Catalyst）的 CountView 视图中计算CoreData ManagedObject Item 的对象数。
第一次直接调用工作正常，第二次在NavigationLists目标中崩溃。

我在做什么错了？

struct ContentView: View {
  @Environment(\.managedObjectContext) var moc
  @FetchRequest(entity: Item.entity(), sortDescriptors: [], predicate: nil) var items: FetchedResults<Item>

  var body: some View {
    NavigationView {
      VStack {
        CountView() // works fine
        NavigationLink("Count", destination: CountView()) //crashes
      }
    }
  }
}

struct CountView: View {
@Environment(\.managedObjectContext) var moc
@FetchRequest(entity: Item.entity(), sortDescriptors: [], predicate: nil) var items: FetchedResults<Item>

  var body: some View
  { Text("Count: \(items.count) ").frame(maxWidth: .infinity, maxHeight: .infinity)
  }
}

在AppDelegate中这样设置上下文：

 func applicationDidFinishLaunching(_ aNotification: Notification) {
   let moc = persistentContainer.viewContext
   let contentView = ContentView().environment(\.managedObjectContext, moc)