UICollectionView + NSFetchedResultsController Swift 3 / iOS 10

UICollectionView + NSFetchedResultsController.swift

    var _fetchedResultsController: NSFetchedResultsController<Entity>? = nil
    var blockOperations: [BlockOperation] = []

    var fetchedResultController: NSFetchedResultsController<Entity> {
        if _fetchedResultsController != nil {
            return _fetchedResultsController!
        }
        
        let fetchRequest: NSFetchRequest<Entity> = Entity.fetchRequest()
        let managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).managedObjectContext!
        
        fetchRequest.predicate = NSPredicate(format: "...")
        
        // sort by item text
        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "...", ascending: true)]
        let resultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
        
        resultsController.delegate = self;
        _fetchedResultsController = resultsController
        
        do {
            try _fetchedResultsController!.performFetch()
        } catch {
            let nserror = error as NSError
            fatalError("Unresolved error \(nserror)")
        }        
        return _fetchedResultsController!
    } 
    
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
        
        if type == NSFetchedResultsChangeType.insert {
            print("Insert Object: \(newIndexPath)")
            
            if (collectionView?.numberOfSections)! > 0 {
                
                if collectionView?.numberOfItems( inSection: newIndexPath!.section ) == 0 {
                    self.shouldReloadCollectionView = true
                } else {
                    blockOperations.append(
                        BlockOperation(block: { [weak self] in
                            if let this = self {
                                DispatchQueue.main.async {
                                    this.collectionView!.insertItems(at: [newIndexPath!])
                                }
                            }
                            })
                    )
                }
                
            } else {
                self.shouldReloadCollectionView = true
            }
        }
        else if type == NSFetchedResultsChangeType.update {
            print("Update Object: \(indexPath)")
            blockOperations.append(
                BlockOperation(block: { [weak self] in
                    if let this = self {
                        DispatchQueue.main.async {
                            
                            this.collectionView!.reloadItems(at: [indexPath!])
                        }
                    }
                    })
            )
        }
        else if type == NSFetchedResultsChangeType.move {
            print("Move Object: \(indexPath)")
            
            blockOperations.append(
                BlockOperation(block: { [weak self] in
                    if let this = self {
                        DispatchQueue.main.async {                          
                            this.collectionView!.moveItem(at: indexPath!, to: newIndexPath!)
                        }
                    }
                    })
            )
        }
        else if type == NSFetchedResultsChangeType.delete {
            print("Delete Object: \(indexPath)")
            if collectionView?.numberOfItems( inSection: indexPath!.section ) == 1 {
                self.shouldReloadCollectionView = true
            } else {
                blockOperations.append(
                    BlockOperation(block: { [weak self] in
                        if let this = self {
                            DispatchQueue.main.async {                     
                                this.collectionView!.deleteItems(at: [indexPath!])
                            }
                        }
                        })
                )
            }        
        }
    }
    
    public func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) {       
        if type == NSFetchedResultsChangeType.insert {
            print("Insert Section: \(sectionIndex)")     
            blockOperations.append(
                BlockOperation(block: { [weak self] in
                    if let this = self {
                        DispatchQueue.main.async {               
                            this.collectionView!.insertSections(NSIndexSet(index: sectionIndex) as IndexSet)
                        }
                    }
                    })
            )
        }
        else if type == NSFetchedResultsChangeType.update {
            print("Update Section: \(sectionIndex)")
            blockOperations.append(
                BlockOperation(block: { [weak self] in
                    if let this = self {
                        DispatchQueue.main.async {           
                            this.collectionView!.reloadSections(NSIndexSet(index: sectionIndex) as IndexSet)
                        }
                    }
                    })
            )
        }
        else if type == NSFetchedResultsChangeType.delete {
            print("Delete Section: \(sectionIndex)")  
            blockOperations.append(
                BlockOperation(block: { [weak self] in
                    if let this = self {
                        DispatchQueue.main.async {          
                            this.collectionView!.deleteSections(NSIndexSet(index: sectionIndex) as IndexSet)
                        }
                    }
                    })
            )
        }
    }
    
    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        
        // Checks if we should reload the collection view to fix a bug @ http://openradar.appspot.com/12954582
        if (self.shouldReloadCollectionView) {
            DispatchQueue.main.async {
                self.collectionView.reloadData();
            }
        } else {
            DispatchQueue.main.async {
                self.collectionView!.performBatchUpdates({ () -> Void in
                    for operation: BlockOperation in self.blockOperations {
                        operation.start()
                    }
                    }, completion: { (finished) -> Void in
                        self.blockOperations.removeAll(keepingCapacity: false)
                })
            }
        }
    }
    
    deinit {
        for operation: BlockOperation in blockOperations {
            operation.cancel()
        }
        blockOperations.removeAll(keepingCapacity: false)
    }