Use old-style collection view datasource so we can use fetchBatchSize to
avoid loading every single item into memory
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@ -15,9 +15,10 @@ class ItemsViewController: UIViewController {
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let fetchRequest: NSFetchRequest<Item>
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private var collectionView: UICollectionView!
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private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
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private var resultsController: NSFetchedResultsController<Item>!
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private var batchUpdates: [() -> Void] = []
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init(fetchRequest: NSFetchRequest<Item>, fervorController: FervorController) {
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self.fervorController = fervorController
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self.fetchRequest = fetchRequest
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@ -37,56 +38,74 @@ class ItemsViewController: UIViewController {
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let layout = UICollectionViewCompositionalLayout.list(using: configuration)
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collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
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collectionView.delegate = self
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collectionView.dataSource = self
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collectionView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
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collectionView.register(ItemCollectionViewCell.self, forCellWithReuseIdentifier: "itemCell")
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view.addSubview(collectionView)
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dataSource = createDataSource()
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var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
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snapshot.appendSections([.items])
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dataSource.apply(snapshot, animatingDifferences: false)
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fetchRequest.sortDescriptors = [NSSortDescriptor(key: "published", ascending: false)]
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fetchRequest.fetchBatchSize = 20
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resultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: fervorController.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
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resultsController.delegate = self
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try! resultsController.performFetch()
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}
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private func createDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
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let itemCell = UICollectionView.CellRegistration<ItemCollectionViewCell, Item> { [unowned self] cell, indexPath, item in
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cell.updateUI(item: item)
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cell.delegate = self
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}
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let dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView) { collectionView, indexPath, item in
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return collectionView.dequeueConfiguredReusableCell(using: itemCell, for: indexPath, item: item)
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}
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return dataSource
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}
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}
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extension ItemsViewController {
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enum Section: Hashable {
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case items
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extension ItemsViewController: UICollectionViewDataSource {
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func numberOfSections(in collectionView: UICollectionView) -> Int {
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return 1
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}
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func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
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return resultsController.fetchedObjects?.count ?? 0
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}
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func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
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let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "itemCell", for: indexPath) as! ItemCollectionViewCell
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cell.delegate = self
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cell.updateUI(item: resultsController.fetchedObjects![indexPath.row])
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return cell
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}
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}
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extension ItemsViewController: NSFetchedResultsControllerDelegate {
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func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith snapshot: NSDiffableDataSourceSnapshotReference) {
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var snapshot = self.dataSource.snapshot()
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snapshot.deleteItems(snapshot.itemIdentifiers(inSection: .items))
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// use resultsController here instead of controller so we don't have to cast
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snapshot.appendItems(resultsController.fetchedObjects!, toSection: .items)
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self.dataSource.apply(snapshot, animatingDifferences: false)
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func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
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batchUpdates = []
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}
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func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
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collectionView.performBatchUpdates {
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for update in self.batchUpdates {
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update()
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}
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}
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// clear to prevent retain cycles
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batchUpdates = []
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}
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func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
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guard let indexPath = indexPath else {
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return
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}
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batchUpdates.append {
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switch type {
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case .insert:
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self.collectionView.insertItems(at: [indexPath])
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case .delete:
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self.collectionView.deleteItems(at: [indexPath])
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case .move:
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if let newIndexPath = newIndexPath {
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self.collectionView.moveItem(at: indexPath, to: newIndexPath)
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}
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case .update:
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self.collectionView.reloadItems(at: [indexPath])
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@unknown default:
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break
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}
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}
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}
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}
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extension ItemsViewController: UICollectionViewDelegate {
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func collectionView(_ collectionView: UICollectionView, contextMenuConfigurationForItemAt indexPath: IndexPath, point: CGPoint) -> UIContextMenuConfiguration? {
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guard let item = dataSource.itemIdentifier(for: indexPath) else {
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return nil
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}
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let item = resultsController.fetchedObjects![indexPath.row]
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return UIContextMenuConfiguration(identifier: nil, previewProvider: {
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ReadViewController(item: item, fervorController: self.fervorController)
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}, actionProvider: { _ in
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