SwiftUI+CoreData重排列表报错：'order'为只读属性

你遇到的Cannot assign to property: 'order' is a get-only property错误，根源在于MyBookmarkViewModel里的order属性只有只读的getter，且内部持有的CoreData实体对象是不可变的let常量，无法直接修改实体的order值。以下是具体修复步骤：

1. 修改MyBookmarkViewModel，让order属性可写 #

把内部的myBM从let改为var，并给order添加setter方法，直接映射到CoreData实体的order属性：

struct MyBookmarkViewModel: Identifiable, Hashable {
    init(myBM: MyBookmark) {
        self.myBM = myBM
    }
    // 将let改为var，允许修改内部CoreData实体
    private var myBM: MyBookmark
    
    var id: NSManagedObjectID {
        myBM.objectID
    }
    
    var name: String {
        myBM.name ?? ""
    }
       
    // 添加getter和setter，直接操作CoreData实体的order属性
    var order: Int64 {
        get { myBM.order }
        set { myBM.order = newValue }
    }
}

2. 完善reorderItems方法，持久化排序修改 #

修改完order值后，必须保存CoreData上下文才能让排序变化永久生效，否则重启App后排序会还原：

func reorderItems(from source: IndexSet, to destination: Int) {
    // 先更新ViewModel数组的内存顺序
    myBookmarks.move(fromOffsets: source, toOffset: destination )

    // 反向遍历更新每个item的order值，避免索引混乱
    for reserveIndex in stride(from: myBookmarks.count - 1, through: 0, by: -1 ) {
        myBookmarks[reserveIndex].order = Int64(reserveIndex)
    }
    
    // 保存CoreData上下文，持久化排序修改
    do {
        try context.save()
    } catch {
        let nsError = error as NSError
        fatalError("排序保存失败: \(nsError), \(nsError.userInfo)")
    }
}

3. 实现FetchedResultsController代理，同步数据变化 #

确保ViewModel能监听CoreData的变化，自动更新myBookmarks数组：

extension MyBookmarksViewModel: NSFetchedResultsControllerDelegate {
    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        guard let fetchedItems = controller.fetchedObjects as? [MyBookmark] else { return }
        myBookmarks = fetchedItems.map(MyBookmarkViewModel.init)
    }
}

同时在ViewModel初始化时执行一次数据拉取，加载初始列表：

init(context: NSManagedObjectContext){
    self.context = context
    self.fetchedResultsController = NSFetchedResultsController(fetchRequest: MyBookmark.all, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    super.init()
    fetchedResultsController.delegate = self
    // 初始加载数据
    do {
        try fetchedResultsController.performFetch()
        if let items = fetchedResultsController.fetchedObjects {
            myBookmarks = items.map(MyBookmarkViewModel.init)
        }
    } catch {
        print("初始数据加载失败: \(error)")
    }
}

内容的提问来源于stack exchange，提问作者swiftnoob