Objective-C method ‘controller:didChangeObject:atIndexPath:forChangeType:newIndexPath:’ provided by method ‘controller(:didChangeObject:atIndexPath:forChangeType:newIndexPath:)’ conflicts with optional requirement method ‘controller(:didChangeObject:atIndexPath:forChangeType:newIndexPath:)’ in protocol ‘NSFetchedResultsControllerDelegate’

func controller(controller: NSFetchedResultsController,didChangeObject anObject: NSManagedObject,atIndexPath indexPath: NSIndexPath?,forChangeType type: NSFetchedResultsChangeType,newIndexPath: NSIndexPath?) {
    if self.collectionView?.window == nil {
        return
    }

    let change = NSMutableDictionary()

    switch(type)
    {
    case .Insert:
        change[NSNumber(unsignedLong:type.rawValue)] = newIndexPath
    case .Delete:
        change[NSNumber(unsignedLong:type.rawValue)] = indexPath
    case .Update:
        change[NSNumber(unsignedLong:type.rawValue)] = indexPath
    case .Move:
        change[NSNumber(unsignedLong:type.rawValue)] = NSArray(objects: indexPath!,newIndexPath!)
    default:
        break
    }
    self.objectChanges?.addObject(change)
}