Question

我有一个名为ToDoItem的实体。其中有三个属性：

@NSManaged var toDoString: String?
@NSManaged var creationDate: NSDate?
@NSManaged var isComplete: NSNumber?

我正在尝试创建NSFetchedResultsController，根据isComplete变量显示两个部分。我能成功地做到这一点：

lazy var fetchedResultsController: NSFetchedResultsController = {

    let questionAnswerFetchRequest = NSFetchRequest(entityName: "ToDoItem")

    let questionAnswerFetchSortDescriptor = NSSortDescriptor(key: "creationDate", ascending: false)
    questionAnswerFetchRequest.sortDescriptors = [questionAnswerFetchSortDescriptor]

    let frc = NSFetchedResultsController(
        fetchRequest: questionAnswerFetchRequest,
        managedObjectContext: (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext,
        sectionNameKeyPath:"isComplete",
        cacheName: nil)

    frc.delegate = self
    return frc
}()

我也实现了这样的删除方法：

//
// MARK: Fetched Results Controller Delegate Methods
//
func controllerWillChangeContent(controller: NSFetchedResultsController) {
    tableView.beginUpdates()
}

func controllerDidChangeContent(controller: NSFetchedResultsController) {
    tableView.endUpdates()
}

func controller(controller: NSFetchedResultsController,
                didChange sectionInfo: NSFetchedResultsSectionInfo,
                          atSectionIndex sectionIndex: Int,
                                         for type: NSFetchedResultsChangeType) {

    switch (type) {
    case .Insert:
        self.tableView.insertSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
        break
    case .Delete:
        self.tableView.deleteSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
        break
    default:
        break
    }

}

func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
    switch (type) {
    case .Insert:
        if let indexPath = newIndexPath {
            tableView.insertRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
        }
        break;
    case .Delete:
        if let indexPath = indexPath {
            tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
        }
        break;
    case .Update:
        if let indexPath = indexPath {
            tableView.reloadRowsAtIndexPaths([indexPath], withRowAnimation: .Automatic)
        }
        break;
    case .Move:
        if let indexPath = indexPath {
            tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
        }

        if let newIndexPath = newIndexPath {
            tableView.insertRowsAtIndexPaths([newIndexPath], withRowAnimation: .Fade)
        }
        break;
    }
}

问题是，当我更新isComplete属性时，我收到此错误：

CoreData：错误：严重的应用程序错误。抓住了一个例外在调用期间来自NSFetchedResultsController的委托 -controllerDidChangeContent :.无效更新：无效的节数。表视图中包含的节数更新（1）必须等于包含的部分数更新前的表视图（0），加号或减号插入或删除的部分（插入0，删除0）。用户信息（空）

我理解这是什么，我只是不明白为什么它导致了这个错误。我根据文档实现了委托方法.....

我更新了我的NSFetchedResultsController创建，为@ wain的答案添加了另一个sortDescriptor，如下所示：

lazy var fetchedResultsController: NSFetchedResultsController = {

        let questionAnswerFetchRequest = NSFetchRequest(entityName: "ToDoItem")

        let isCompleteSortDescriptor   = NSSortDescriptor(key: "isComplete", ascending: false)
        let creationDateSortDescriptor = NSSortDescriptor(key: "creationDate", ascending: false)

        questionAnswerFetchRequest.sortDescriptors = [isCompleteSortDescriptor, creationDateSortDescriptor]

        let frc = NSFetchedResultsController(
            fetchRequest: questionAnswerFetchRequest,
            managedObjectContext: (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext,
            sectionNameKeyPath:"isComplete",
            cacheName: nil)

        frc.delegate = self
        return frc
    }()

我添加了一些断点，事实证明这个委托方法永远不会被调用：

func controller(controller: NSFetchedResultsController,
                didChange sectionInfo: NSFetchedResultsSectionInfo,
                          atSectionIndex sectionIndex: Int,
                                         for type: NSFetchedResultsChangeType) {

    switch (type) {
    case .Insert:
        self.tableView.insertSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
        break
    case .Delete:
        self.tableView.deleteSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
        break
    default:
        break
    }
}

导致与上面发布的错误相同的错误。关于为什么永远不会被召唤的任何想法？

Answer 1

您需要为isComplete添加排序描述符。它应该是第一个排序描述符，然后是你的日期。

基本上，排序和部分需要兼容，而你的目前不是。

使用NSFetchedResultsController更新节

1 个答案: