NSFetchedResultsControllerDelegate for UICollectionView

FRCCollectionViewDataSource.swift

protocol FRCCollectionViewDelegate: class {
	func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
}

class FRCCollectionViewDataSource<FetchRequestResult: NSFetchRequestResult>: NSObject, UICollectionViewDataSource, NSFetchedResultsControllerDelegate {
	
	let frc: NSFetchedResultsController<FetchRequestResult>
	weak var collectionView: UICollectionView?
	weak var delegate: FRCCollectionViewDelegate?
	
	private var blockOperation = BlockOperation()
	
	init(fetchRequest: NSFetchRequest<FetchRequestResult>, context: NSManagedObjectContext, sectionNameKeyPath: String?) {
		frc = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: sectionNameKeyPath, cacheName: nil)
		
		super.init()
		
		frc.delegate = self
	}
	
	func performFetch() throws {
		try frc.performFetch()
	}
	
	func object(at indexPath: IndexPath) -> FetchRequestResult {
		return frc.object(at: indexPath)
	}
	
	// MARK: - UICollectionViewDataSource
	
	func numberOfSections(in collectionView: UICollectionView) -> Int {
		return frc.sections?.count ?? 0
	}
	
	func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
		guard let sections = frc.sections else { return 0 }
		
		return sections[section].numberOfObjects
	}
	
	func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
		if let delegate = delegate {
			return delegate.collectionView(collectionView, cellForItemAt: indexPath)
		} else {
			return UICollectionViewCell()
		}
	}
	
	// MARK: - NSFetchedResultsControllerDelegate
	
	func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
		blockOperation = BlockOperation()
	}

	func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) {
		let sectionIndexSet = IndexSet(integer: sectionIndex)

		switch type {
		case .insert:
			blockOperation.addExecutionBlock {
				self.collectionView?.insertSections(sectionIndexSet)
			}
		case .delete:
			blockOperation.addExecutionBlock {
				self.collectionView?.deleteSections(sectionIndexSet)
			}
		case .update:
			blockOperation.addExecutionBlock {
				self.collectionView?.reloadSections(sectionIndexSet)
			}
		case .move:
			assertionFailure()
			break
		}
	}
	
	func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
		switch type {
		case .insert:
			guard let newIndexPath = newIndexPath else { break }
			
			blockOperation.addExecutionBlock {
				self.collectionView?.insertItems(at: [newIndexPath])
			}
		case .delete:
			guard let indexPath = indexPath else { break }
			
			blockOperation.addExecutionBlock {
				self.collectionView?.deleteItems(at: [indexPath])
			}
		case .update:
			guard let indexPath = indexPath else { break }
			
			blockOperation.addExecutionBlock {
				self.collectionView?.reloadItems(at: [indexPath])
			}
		case .move:
			guard let indexPath = indexPath, let newIndexPath = newIndexPath else { return }
			
			blockOperation.addExecutionBlock {
				self.collectionView?.moveItem(at: indexPath, to: newIndexPath)
			}
		}
	}
	
	func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
		collectionView?.performBatchUpdates({
			self.blockOperation.start()
			}, completion: nil)
	}
	
}

The current version does not work on iOS 12 as the NSBlockOperation blocks are executed parallel on background threads but need to be performed on the main thread.

@tengelmeier any solution for this ?

My UI freezes during significant, multi-object sync operations via iCloud; is it possible the cause is what @tengelmeier commented?
Update: It seems that the approach used in this 2020 Stack Overflow answer is not causing the UI to be frozen.