NSFetchedResultsController inserts the same cell into two sections only when controller is about to insert another section

Question

This is my Message.swift file:

@objc(Message)
class Message: NSManagedObject {

    @NSManaged var content: String
    @NSManaged var createdAt:         


        

Answer 1

I do not know why, but to make it working you need to replace:

fetchedResultsController.sections![section].objects!.count

with

fetchedResultsController.sections![section].numberOfObjects

For some reason objects!.count returns incorrect number of objects opposite to numberOfObjects property.

Answer 2

I tried your code, made only one change, this:

var normalizedCreatedAt: String {
    return getTimeStrWithDayPrecision(createdAt!)
}

func getTimeStrWithDayPrecision(date: NSDate) -> String {
    let formatter = NSDateFormatter()
    formatter.timeStyle = .NoStyle
    formatter.dateStyle = .ShortStyle
    formatter.doesRelativeDateFormatting = true
    return formatter.stringFromDate(date)
}

and it works fine, even for 2nd section also!

For demo purpose, I added ADD button, by pressing it, code will add new message with current date string as content to DB.

Here is my complete implementation: View controller-

class ChatTableViewController: UITableViewController, NSFetchedResultsControllerDelegate {


private var fetchedResultsController: NSFetchedResultsController?
private var _mainThreadMOC: NSManagedObjectContext?

override func viewDidLoad() {
    super.viewDidLoad()

    // Uncomment the following line to preserve selection between presentations
    // self.clearsSelectionOnViewWillAppear = false

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem()
    
    setupFetchedResultsController()
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

private func getMainMOC() -> NSManagedObjectContext {
    if _mainThreadMOC == nil {
        let appDel = UIApplication.sharedApplication().delegate as! AppDelegate
        _mainThreadMOC = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
        _mainThreadMOC!.persistentStoreCoordinator = appDel.persistentStoreCoordinator
        _mainThreadMOC!.undoManager = nil
    }
    return _mainThreadMOC!
}

private func setupFetchedResultsController() {
    
    let fetchRequest = NSFetchRequest(entityName: "Message")
    let createdAtDescriptor = NSSortDescriptor(key: "createdAt", ascending: true)
    fetchRequest.sortDescriptors = [createdAtDescriptor]
    
    fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: getMainMOC(), sectionNameKeyPath: "normalizedCreatedAt", cacheName: nil)
    fetchedResultsController!.delegate = self
    
    try! fetchedResultsController!.performFetch()
    tableView.reloadData()
}

@IBAction func addMessage(sender: AnyObject) {
    print("addMessage")
    
    let MOC = getMainMOC()
    let date = NSDate()
    let _ = Message(text: "\(date)", moc: MOC)
    do {
        try MOC.save()
    }catch {
        print("Error saving main MOC: \(error)")
    }
    
}

// MARK: - Table view data source

override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    return fetchedResultsController?.sections?.count ?? 0
}

override func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
    let sectionInfo = fetchedResultsController!.sections! as [NSFetchedResultsSectionInfo]
    let title = sectionInfo[section].name
    
    let headerHeight:CGFloat = tableView.sectionHeaderHeight
    let headerLbl = UILabel(frame: CGRectMake(0, 0, tableView.frame.width, headerHeight))
    headerLbl.backgroundColor = UIColor.lightGrayColor()
    headerLbl.textAlignment = .Center
    headerLbl.text = title
    return headerLbl
}

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    print("--->>>")
    print(section)
    print(fetchedResultsController?.sections![section].objects!.count)
    return (fetchedResultsController?.sections![section].objects!.count)!
}

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    
    let message = fetchedResultsController?.objectAtIndexPath(indexPath) as! Message
    let cell = tableView.dequeueReusableCellWithIdentifier("MessageCellId", forIndexPath: indexPath)
    
    cell.textLabel?.text = message.content!
    
    return cell
}
//MARK: - NSFetchedResultsControllerDelegate

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

func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {
    
    let indexSet = NSIndexSet(index: sectionIndex)
    
    switch type {
    case .Insert:
        
        tableView.insertSections(indexSet, withRowAnimation: .Fade)
        
    case .Delete:
        
        tableView.deleteSections(indexSet, withRowAnimation: .Fade)
        
    case .Update:
        
        fallthrough
        
    case .Move:
        
        tableView.reloadSections(indexSet, withRowAnimation: .Fade)
    }
}

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

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

Message-

func getTimeStrWithDayPrecision(date: NSDate) -> String {
let formatter = NSDateFormatter()
formatter.timeStyle = .NoStyle
formatter.dateStyle = .ShortStyle
formatter.doesRelativeDateFormatting = true
return formatter.stringFromDate(date)
}

extension Message {

@NSManaged var content: String?
@NSManaged var createdAt: NSDate?

var normalizedCreatedAt: String {
    return getTimeStrWithDayPrecision(createdAt!)
}    
}

class Message: NSManagedObject {

// Insert code here to add functionality to your managed object subclass

override init(entity: NSEntityDescription, insertIntoManagedObjectContext context: NSManagedObjectContext?) {
    super.init(entity: entity, insertIntoManagedObjectContext: context)
}

init(text: String, moc:NSManagedObjectContext) {
    let entity = NSEntityDescription.entityForName("Message", inManagedObjectContext: moc)
    super.init(entity: entity!, insertIntoManagedObjectContext: moc)
    content = text
    createdAt = NSDate()
}
}

Here is the iPad screenshot:

For testing multiple sections, I changed date & time setting os iPad.