如何使用NSFetchedResultsController在表視圖控制器中添加節（帶有自定義標題單元格）？

Question

我正在制作一個具有可擴展表的表視圖，其中的節（束）是自定義UITableViewCell以及行（伙伴）-您可以創建任意一堆的伙伴。 我還使用NSFetchedResultsController填充了表，這已成功完成。 我遇到的困難是將一堆數據添加到核心數據時，NSFetchedResultsController拋出此異常：

CoreData：錯誤：嚴重的應用程序錯誤。 在調用-controllerDidChangeContent：期間，從NSFetchedResultsController的委托捕獲了一個異常。 嘗試將第0行插入第1節，但是在使用userInfo更新后，第1節中只有0行（空）

我希望能夠添加一堆（在模式對話框中），並使其自動顯示在表格視圖中（根據NSFetchedResultController功能），但是會引發異常（盡管不會崩潰），如上和本節所示未添加。

這是NSFetchedResultsController的代碼：

初始化 （在加載表視圖時初始化）

lazy var fetchedResultsController: NSFetchedResultsController = {
    let bunchesFetchRequest = NSFetchRequest(entityName: Constants.CoreData.bunch)
    // Sort bunches by bunch name, in alphabetical order, not caring about capitalization
    let primarySortDescriptor = NSSortDescriptor(key: Constants.CoreData.Bunch.name, ascending: true, selector: "caseInsensitiveCompare:")
    bunchesFetchRequest.sortDescriptors = [primarySortDescriptor]

    // TODO: Answer question: Do we need this, does this benefit us at all, and how does prefetching work?
    bunchesFetchRequest.relationshipKeyPathsForPrefetching = [Constants.CoreData.Bunch.buddies]

    let frc = NSFetchedResultsController(
        fetchRequest: bunchesFetchRequest,
        managedObjectContext: CoreDataStackManager.sharedInstance().managedObjectContext!,
        sectionNameKeyPath: Constants.CoreData.Bunch.name,
        cacheName: nil
    )
    frc.delegate = self
    return frc
}()

表格檢視方法

func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    // sections are the bunches
    if let sections = fetchedResultsController.sections {
        return sections.count
    }
    return 0
}

func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    // sections are the bunches (this is for when sectionNameKeyPath is set)
    if let sections = fetchedResultsController.sections {
        let currentSection = sections[section] as! NSFetchedResultsSectionInfo
        let bunch = currentSection.objects[0] as! Bunch
        // Return the number of buddies in this section (bunch)
        return bunch.buddies.count
    }
    return 0
}


func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {

    if let sections = fetchedResultsController.sections {
        let currentSection = sections[section] as! NSFetchedResultsSectionInfo
        let bunch = currentSection.objects[0] as! Bunch
            // Create BunchTableViewCell
        let headerCell: BunchTableViewCell = tableView.dequeueReusableCellWithIdentifier(bunchCellIdentifier) as! BunchTableViewCell

        headerCell.bunchNameLabel.text = bunch.name    
        return headerCell
    }
    return nil
}

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    let cell: BuddyInBunchTableViewCell = tableView.dequeueReusableCellWithIdentifier(buddyInBunchCellIdentifier, forIndexPath: indexPath) as! BuddyInBunchTableViewCell

    if let sections = fetchedResultsController.sections {
        let currentSection = sections[indexPath.section] as! NSFetchedResultsSectionInfo
        let bunch = currentSection.objects[0] as! Bunch
        let buddy: Buddy = bunch.getBuddiesInBunch()[indexPath.row]
        cell.buddyFullNameLabel.text = buddy.getFullName()
    }
    return cell
}

func tableView(tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
    return 50.0 
}

NSFetchedResultsController方法

func controllerWillChangeContent(controller: NSFetchedResultsController) {
    self.tableView.beginUpdates()
}

func controller(
    controller: NSFetchedResultsController,
    didChangeObject anObject: AnyObject,
    atIndexPath indexPath: NSIndexPath?,
    forChangeType type: NSFetchedResultsChangeType,
    newIndexPath: NSIndexPath?) {

        switch type {
        case NSFetchedResultsChangeType.Insert:
            // Note that for Insert, we insert a row at the __newIndexPath__
            if let insertIndexPath = newIndexPath {
                // AAAAAAAAAA
                self.tableView.insertRowsAtIndexPaths([insertIndexPath], withRowAnimation: UITableViewRowAnimation.Fade)
                // BBBBBBBBBB
                // self.tableView.insertSections(NSIndexSet(index: insertIndexPath.section), withRowAnimation: UITableViewRowAnimation.Fade)
            }
        case NSFetchedResultsChangeType.Delete:
            // Note that for Delete, we delete the row at __indexPath__
            if let deleteIndexPath = indexPath {
                self.tableView.deleteRowsAtIndexPaths([deleteIndexPath], withRowAnimation: UITableViewRowAnimation.Fade)
            }
        case NSFetchedResultsChangeType.Update:
            // Note that for Update, we update the row at __indexPath__
            // Not yet implemented
            break
        case NSFetchedResultsChangeType.Move:
            // Note that for Move, we delete the row at __indexPath__
            if let deleteIndexPath = indexPath {
                self.tableView.deleteRowsAtIndexPaths([deleteIndexPath], withRowAnimation: UITableViewRowAnimation.Fade)
            }

            // Note that for Move, we insert a row at the __newIndexPath__
            if let insertIndexPath = newIndexPath {
                self.tableView.insertRowsAtIndexPaths([insertIndexPath], withRowAnimation: UITableViewRowAnimation.Fade)
            }
        }
}


func controller(
    controller: NSFetchedResultsController,
    didChangeSection sectionInfo: NSFetchedResultsSectionInfo,
    atIndex sectionIndex: Int,
    forChangeType type: NSFetchedResultsChangeType) {

        switch type {
        case .Insert:
            // AAAAAAAAAA
            let sectionIndexSet = NSIndexSet(index: sectionIndex)
            self.tableView.insertSections(sectionIndexSet, withRowAnimation: UITableViewRowAnimation.Fade)
            // BBBBBBBBBBB
            // break
        case .Delete:
            let sectionIndexSet = NSIndexSet(index: sectionIndex)
            self.tableView.deleteSections(sectionIndexSet, withRowAnimation: UITableViewRowAnimation.Fade)
        default:
            break
        }
}

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

注意：如果我注釋掉AAAAAAAAAA下的行並取消注釋BBBBBBBBBB中的行，則可以看到該單元格顯示的非常簡短，但是插入的單元格下面的每個單元格都消失了，而是多次出現此錯誤：

沒有重用表單元格的索引路徑

任何幫助/建議表示贊賞！

Answer 1

好吧，我發現：

“ NSFetchedResultsController的更大問題之一是它無法顯示空白部分。”

在此博客文章中提到了解決該問題的方法（注意：我尚未實現此方法，但我現在知道以直觀的方式是不可能的）。