我在使用 NSFetchedResultsController 时遇到了一些问题。

我有子类 FRC

class InboxFetchResultsController: NSFetchedResultsController {

    override init() {
        let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

        let fetchRequest = NSFetchRequest(entityName: "Compliment")

        let firstSortDescriptor = NSSortDescriptor(key: "updatedAt", ascending: false)
        let secondSortDescriptor = NSSortDescriptor(key: "sendedDate", ascending: false)
        fetchRequest.sortDescriptors = [firstSortDescriptor, secondSortDescriptor]
        let privateManagedObjectContext = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
        privateManagedObjectContext.parentContext = appDelegate.cdh.managedObjectContext
        let user = try! privateManagedObjectContext.existingObjectWithID(CoreDataManager.sharedInstance.getLoggedUser().objectID) as! User

        let predicate = NSPredicate(format: "recievedBelong = %@", user)

        fetchRequest.predicate = predicate

        super.init(fetchRequest: fetchRequest, managedObjectContext: privateManagedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
//
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(contextDidSaveContext(_:)), name: NSManagedObjectContextDidSaveNotification, object: nil)
    }


    deinit{
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }

    func contextDidSaveContext(notification: NSNotification) {
        let sender = notification.object as! NSManagedObjectContext
        if sender != managedObjectContext {
            self.managedObjectContext.performBlock({ [weak self] in
                DDLogInfo("Core data merging")
                self!.managedObjectContext.mergeChangesFromContextDidSaveNotification(notification)
            })

        }
    }

}

还有 ComplimentsViewController

lazy var fetchedResultsController: NSFetchedResultsController = {
    let fetchedResultsController = InboxFetchResultsController()
    fetchedResultsController.delegate = self
    fetchedResultsController.fetchRequest.predicate = self.receivedPredicate
    return fetchedResultsController
}()

在我调用的 viewDidLoad 中

  func performFetch() {
    fetchedResultsController.managedObjectContext.performBlock { [weak self] in
        do {
            try self!.fetchedResultsController.performFetch()
        } catch {
            let fetchError = error as NSError
            print("\(fetchError), \(fetchError.userInfo)")
        }
        dispatch_async(dispatch_get_main_queue(), {
            self!.tableView.reloadData()
        })
    }

与

extension ComplimentsViewController: NSFetchedResultsControllerDelegate {
    func controllerWillChangeContent(controller: NSFetchedResultsController) {
        dispatch_async(dispatch_get_main_queue(), {
            self.tableView.beginUpdates()
        })
    }

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

    }
    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;
        }
    }

我正在不同的 View Controller 中编辑获取的对象，使用在后台 Context 上分配的 ViewModel。 当我保存那个背景上下文时，我得到了那个错误:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of rows in section 0.  The number of rows contained in an existing section after the update (5) must be equal to the number of rows contained in that section before the update (5), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).'
*** First throw call stack:

我花了几个小时来处理并发性， 检查 tableView 委托(delegate)方法的时间... 仍然遇到那个问题。

最佳答案

你正在使用 NSFetchedResultsController 所以你不应该调用:

    dispatch_async(dispatch_get_main_queue(), {
        self!.tableView.reloadData()
    })

因为所有 NSFetchedResultsControllerDelegate 方法都在这里更新你的 tableView，它会自动触发。

此外，您在 Swift 中不需要分号，也不需要 break; 在您的 switch 中，默认行为是 break，除非您明确提及 fallthrough

关于ios - nsfetchedResultsController - 合并数据时出错，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/36558438/