nsfetchedResultsController - error when merging data - ios

Question

I had some issue with NSFetchedResultsController.
I had subclass 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)
})
}
}
}
And with ComplimentsViewController
lazy var fetchedResultsController: NSFetchedResultsController = {
let fetchedResultsController = InboxFetchResultsController()
fetchedResultsController.delegate = self
fetchedResultsController.fetchRequest.predicate = self.receivedPredicate
return fetchedResultsController
}()
In viewDidLoad I'm calling
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()
})
}
with
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;
}
}
I'm editing fetched object in different View Controller, using ViewModel, that is allocated on background Context.
When I save that background context, I get that error:
*** 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:
I spend hours to take care about the concurrency,
hours to check the tableView delegate methods...
And still get that issue.

Answer 1

You're using NSFetchedResultsController so you shouldn't call :
dispatch_async(dispatch_get_main_queue(), {
self!.tableView.reloadData()
})
Since the all NSFetchedResultsControllerDelegate method are here to update your tableView, it will be triggered automatically.
Also you don't need semicolon in Swift, neither to break; in your switch the default behavior is to break unless you explicitly mention fallthrough