A generic reusable NSFetchedResultsControllerDelegate.

GenericCollectionFetchResultsController.swift

import UIKit
import CoreData

class GenericCollectionFetchResultsController: NSObject {
    
    fileprivate var blockOperation = BlockOperation()
    //This flag is a workaround to a bug in iOS: http://openradar.appspot.com/12954582
    fileprivate var shouldReloadCollectionView = false
    fileprivate var collectionView: UICollectionView!
    
    init(collectionView: UICollectionView) {
        self.collectionView = collectionView
    }
    
    deinit {
        blockOperation.cancel()
    }
}

extension GenericCollectionFetchResultsController: NSFetchedResultsControllerDelegate {
    
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
        switch type {
            
        case .insert:
            if collectionView.numberOfSections > 0 {
                if collectionView.numberOfItems(inSection: newIndexPath!.section) == 0 {
                    shouldReloadCollectionView = true
                } else {
                    blockOperation.addExecutionBlock {
                        self.collectionView.insertItems(at: [newIndexPath!])
                    }
                }
            } else {
                shouldReloadCollectionView = true
            }
            
        case .update:
            blockOperation.addExecutionBlock {
                self.collectionView.reloadItems(at: [indexPath!])
            }
            
        case .move:
            blockOperation.addExecutionBlock {
                self.collectionView.moveItem(at: indexPath!, to: newIndexPath!)
            }
            
        case .delete:
            if collectionView.numberOfItems(inSection: indexPath!.section) == 1 {
                shouldReloadCollectionView = true
            } else {
                blockOperation.addExecutionBlock {
                    self.collectionView.deleteItems(at: [indexPath!])
                }
            }
        }
    }
    

    
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) {
        
        switch type {
        case .insert:
            blockOperation.addExecutionBlock {
                self.collectionView.insertSections(IndexSet(integer: sectionIndex))
            }
            
        case .update:
            blockOperation.addExecutionBlock {
                self.collectionView.reloadSections(IndexSet(integer: sectionIndex))
            }
            
        case .delete:
            blockOperation.addExecutionBlock {
                self.collectionView.deleteSections(IndexSet(integer: sectionIndex))
            }
            
        default: break
        
        }
    }
    
    func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        shouldReloadCollectionView = false
        blockOperation = BlockOperation()
    }
    
    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        DispatchQueue.main.async {
            if self.shouldReloadCollectionView {
                self.collectionView.reloadData()
            } else {
                self.collectionView.performBatchUpdates({
                    self.blockOperation.start()
                }, completion: nil)
            }
        }
    }
}