Question

我对Swift和Core Data很陌生，但我认为我掌握了基础知识。但是，我有一个简单的核心数据模型的问题，我想抓住与多对多关系中的另一个实体相关的所有实体。我想要做的是在表视图中选择一个父对象，并在另一个视图中显示其子元素。

所以我使用以下代码从ParentsVC传递父对象：

  func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
        let CHILDREN_TAB_INDEX = 1
        var navigationController = self.tabBarController?.viewControllers?[CHILDREN_TAB_INDEX] as UINavigationController
        if navigationController.topViewController is ChildrenVC {
            var childrenVC = navigationController.topViewController as ChildrenVC
            let parent = self.fetchedResultsController.objectAtIndexPath(self.menuTableView.indexPathForSelectedRow()!) as Parent
            childrenVC.currentParent = parent
            self.tabBarController?.selectedIndex = CHILDREN_TAB_INDEX
        }
    }

然后在ChildrenVC中，我执行以下提取以获取子对象：

var _fetchedResultsController: NSFetchedResultsController? = nil

var fetchedResultsController: NSFetchedResultsController {
    if _fetchedResultsController != nil {
        return _fetchedResultsController!
    }
    let moc:NSManagedObjectContext = coreDataHelper.backgroundContext!
    let fetchRequest = NSFetchRequest()
    let entity = NSEntityDescription.entityForName("Child", inManagedObjectContext: moc)
    fetchRequest.entity = entity
    fetchRequest.fetchBatchSize = 20
    let sortDescriptor = NSSortDescriptor(key: "name", ascending: false)
    let predicate = NSPredicate(format: "parent == %@", self.currentParent)
    fetchRequest.predicate = predicate
    let sortDescriptors = [sortDescriptor]
    fetchRequest.sortDescriptors = [sortDescriptor]

    let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: moc, sectionNameKeyPath: nil, cacheName: "Master")
        aFetchedResultsController.delegate = self
        _fetchedResultsController = aFetchedResultsController

    var error: NSError? = nil
    if !_fetchedResultsController!.performFetch(&error) {
        abort()
        }
    _fetchedResultsController?.delegate = self
    return _fetchedResultsController!
}

添加新子代码的代码（在ParentsVC中完成）：

func addNewParent(parentName:String) {
    let moc:NSManagedObjectContext = coreDataHelper.backgroundContext!
    var parent:Parent = NSEntityDescription.insertNewObjectForEntityForName("Parent", inManagedObjectContext: moc) as Parent
    parent.name = parentName
    for n in 1...5 {
        var child:Child = NSEntityDescription.insertNewObjectForEntityForName("Child", inManagedObjectContext: moc) as Child
        child.name = "A"
        child.parent = parent
    }
    coreDataHelper.saveContext(moc)
    menuTableView.reloadData()
}

不是根据我点击的父级列出不同的子元素，而是根据我选择的父级获得相同的子项（子项在ChildrenVC中可编辑，因此我可以区分）。但是当我重新启动/重建应用程序时，我会随机获得另一组为所有父母显示的子项。我在这里缺少什么？

Answer 1

发现它！我只是忘了在ChildrenVC中重置self._fetchedResultsController。所以传递对象的代码应该是：

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    let CHILDREN_TAB_INDEX = 1
    var navigationController = self.tabBarController?.viewControllers?[CHILDREN_TAB_INDEX] as UINavigationController
    if navigationController.topViewController is ChildrenVC {
        var childrenVC = navigationController.topViewController as ChildrenVC
        let parent = self.fetchedResultsController.objectAtIndexPath(self.menuTableView.indexPathForSelectedRow()!) as Parent
        childrenVC.currentParent = parent
        childrenVC._fetchedResultsController = nil
        self.tabBarController?.selectedIndex = CHILDREN_TAB_INDEX
    }
}

我的Swift获取请求返回具有错误关系的对象

1 个答案: