iOS8 Swift: deleteRowsAtIndexPaths crashes

Question

I am having some trouble with deleting a row from my tableView in Swift, iOS 8, Xcode 6 Beta 6. Every time I try to delete a row I get an error along the lines of

Answer 1

I believe this is simply a caching problem. Your fetchedResultController is not going to automatically refetch your results as it caches its results. That means that when tableView:numberOfRowsInSection: is called again, the results count is still returning 25 even though you deleted an item.

Answer 2

It's easy to reproduce your crash with a Xcode Core Data Master-Detail template project. As a general rule, when you use NSFetchedResultsController, you should really use NSFetchedResultsControllerDelegate (you have declared it but don't use it).

Delete those lines in your tableView:commitEditingStyle:forRowAtIndexPath: method:

tableViewMain.beginUpdates()
tableViewMain!.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: UITableViewRowAnimation.Fade)
tableViewMain.endUpdates()

And add those lines to your viewController class:

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

func controller(controller: NSFetchedResultsController!, didChangeSection sectionInfo: NSFetchedResultsSectionInfo!, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {
    switch type {
    case .Insert:
        tableViewMain.insertSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
    case .Delete:
        tableViewMain.deleteSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
    default:
        return
    }
}

func controller(controller: NSFetchedResultsController!, didChangeObject anObject: AnyObject!, atIndexPath indexPath: NSIndexPath!, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath!) {
    switch type {
    case .Insert:
        tableViewMain.insertRowsAtIndexPaths([newIndexPath], withRowAnimation: .Fade)
    case .Delete:
        tableViewMain.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
    case .Update:
        return
        //Should also manage this case!!!
        //self.configureCell(tableView.cellForRowAtIndexPath(indexPath), atIndexPath: indexPath)
    case .Move:
        tableViewMain.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
        tableViewMain.insertRowsAtIndexPaths([newIndexPath], withRowAnimation: .Fade)
    default:
        return
    }
}

func controllerDidChangeContent(controller: NSFetchedResultsController!) {
    tableViewMain.endUpdates()
}

This should fix your problem.