如何使用ObservedObject和NSManagedObject制作Picker？

Question

在我看来，我定义了一些ObservedObjects。 ShoppingItems和Packages是NSManagedObject子类。

    @ObservedObject var shoppingListData: ShoppingListData
    @ObservedObject var shoppingItem: ShoppingItems
    @ObservedObject var package: Packages

    init(thisData: ShoppingListData, formShoppingItem: ShoppingItems, formPackage: Packages?) {
        shoppingListData = thisData
        shoppingItem = formShoppingItem

        if let fp = formPackage {
            package = fp
        } else if let fp = formShoppingItem.minStorePackage {
            package = fp
        } else {
            let newPackage = Packages(context: thisData.dataStack.moc)
            newPackage.myShoppingItem = formShoppingItem
            newPackage.myStore = thisData.dataStack.currentReceipt.myStore!
            package = newPackage
        }
    }

我体内有一个选择器。

 Picker(selection: $package, label: Text("Store Packages")) {
     ForEach(shoppingItem.storePackages, id: \.uuidKey) { pkg in
         Text(pkg.brandName).tag(pkg.uuidKey)         
     }
 }

选择器将显示其他软件包，但不会将软件包变量从旧软件包更改为新选择的软件包。 SwiftUI是否有一些限制，无法在视图初始化后更改@ObservedObject指向哪个实例？