Simple example of how to use in a UIViewController with a CoreData Entity called Game.
Create variable.
var fetchedResultsController: NSFetchedResultsController<Game>!Load via CoreData. Here you can specify how you would like your results to be fetched, give a sort description, and limit the number of results coming back while also setting yourself up as the delegate to receive callbacks. This is also where we load the tableView data.
func loadSavedData() {
if fetchedResultsController == nil {
let request = NSFetchRequest<Game>(entityName: "Game")
let sort = NSSortDescriptor(key: "name", ascending: false)
request.sortDescriptors = [sort]
request.fetchBatchSize = 20
fetchedResultsController = NSFetchedResultsController(fetchRequest: request, managedObjectContext: viewContext, sectionNameKeyPath: nil, cacheName: nil)
fetchedResultsController.delegate = self
}
do {
try fetchedResultsController.performFetch()
tableView.reloadData()
} catch {
print("Fetch failed")
}
}When add button is pressed, we can create a new Game Entitiy via CoreData.
@objc
func addButtonPressed() {
guard let name = textField.text else { return }
// 4 CoreData viewContext > NSFetchRequest > Delegate (us)
GameManager.shared.createGame(name: name)
}In the UIDataSource we get the data for our tableCell from the fetchResultsController.
extension DemoFetchedResultsViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath)
// 5
// cell.textLabel?.text = games[indexPath.row]
let game = fetchedResultsController.object(at: indexPath)
cell.textLabel?.text = game.name
cell.accessoryType = UITableViewCell.AccessoryType.none
return cell
}
Then we can add our trailingSwipeActions only with their respective handlers in the event of a delete. Note here how we fetch the object to delete first from the fetchResultsController and then pass it to our CoreData viewContext to delete.
func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
let action = UIContextualAction(style: .destructive, title: "Delete", handler: { (action, view, completionHandler) in
// 6a. Delete CoreData here
let game = self.fetchedResultsController.object(at: indexPath)
GameManager.shared.persistentContainer.viewContext.delete(game)
GameManager.shared.saveContext()
})
action.image = makeSymbolImage(systemName: "trash")
let configuration = UISwipeActionsConfiguration(actions: [action])
return configuration
}Then update the table only after the fetchResultsController calls us back. This is a three step process: willChangeContent, didChange, didChangeContent.
extension DemoFetchedResultsViewController: NSFetchedResultsControllerDelegate {
func numberOfSections(in tableView: UITableView) -> Int {
return fetchedResultsController.sections?.count ?? 0
}
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.beginUpdates() // a
}
// 6b Update table via delegate callback here.
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
switch type {
case .insert:
tableView.insertRows(at: [newIndexPath!], with: .fade) // b
case .delete:
tableView.deleteRows(at: [indexPath!], with: .fade)
case .update:
tableView.reloadRows(at: [indexPath!], with: .fade)
case .move:
tableView.moveRow(at: indexPath!, to: newIndexPath!)
default:
break
}
}
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.endUpdates() // c
}
}Full source.
//
// DemoFetchedResultsViewController.swift
// DemoArcade
//
// Created by Jonathan Rasmusson Work Pro on 2020-03-16.
// Copyright © 2020 Rasmusson Software Consulting. All rights reserved.
//
import UIKit
import CoreData
class DemoFetchedResultsViewController: UIViewController {
// Replacing array with CoreData
// var games = ["Space Invaders",
// "Dragon Slayer",
// "Disks of Tron",
// "Moon Patrol",
// "Galaga"]
// 1
var fetchedResultsController: NSFetchedResultsController<Game>!
let viewContext = GameManager.shared.persistentContainer.viewContext
let textField: UITextField = {
let textField = UITextField()
textField.translatesAutoresizingMaskIntoConstraints = false
textField.font = UIFont.preferredFont(forTextStyle: .body)
textField.textAlignment = .center
textField.backgroundColor = .systemFill
return textField
}()
lazy var addButton: UIButton = {
let button = makeButton(withText: "Add")
button.setContentHuggingPriority(UILayoutPriority.defaultHigh, for: .horizontal)
button.addTarget(self, action: #selector(addButtonPressed), for: .primaryActionTriggered)
return button
}()
var tableView: UITableView = {
let tableView = UITableView()
tableView.translatesAutoresizingMaskIntoConstraints = false
return tableView
}()
let cellId = "insertCellId"
override func viewDidLoad() {
super.viewDidLoad()
layout()
loadSavedData()
setupTableView()
}
func setupTableView() {
tableView.dataSource = self
tableView.register(UITableViewCell.self, forCellReuseIdentifier: cellId)
}
func layout() {
navigationItem.title = "Fetched Results Demo"
let addStackView = makeHorizontalStackView()
addStackView.addArrangedSubview(textField)
addStackView.addArrangedSubview(addButton)
view.addSubview(addStackView)
view.addSubview(tableView)
addStackView.topAnchor.constraint(equalToSystemSpacingBelow: view.safeAreaLayoutGuide.topAnchor, multiplier: 3).isActive = true
addStackView.leadingAnchor.constraint(equalToSystemSpacingAfter: view.leadingAnchor, multiplier: 3).isActive = true
view.trailingAnchor.constraint(equalToSystemSpacingAfter: addStackView.trailingAnchor, multiplier: 3).isActive = true
tableView.topAnchor.constraint(equalToSystemSpacingBelow: addStackView.bottomAnchor, multiplier: 1).isActive = true
tableView.leadingAnchor.constraint(equalToSystemSpacingAfter: view.leadingAnchor, multiplier: 1).isActive = true
view.trailingAnchor.constraint(equalToSystemSpacingAfter: tableView.trailingAnchor, multiplier: 1).isActive = true
view.safeAreaLayoutGuide.bottomAnchor.constraint(equalToSystemSpacingBelow: tableView.bottomAnchor, multiplier: 1).isActive = true
}
// 3
func loadSavedData() {
if fetchedResultsController == nil {
let request = NSFetchRequest<Game>(entityName: "Game")
let sort = NSSortDescriptor(key: "name", ascending: false)
request.sortDescriptors = [sort]
request.fetchBatchSize = 20
fetchedResultsController = NSFetchedResultsController(fetchRequest: request, managedObjectContext: viewContext, sectionNameKeyPath: nil, cacheName: nil)
fetchedResultsController.delegate = self
}
do {
try fetchedResultsController.performFetch()
tableView.reloadData()
} catch {
print("Fetch failed")
}
}
// MARK: - Actions
@objc
func addButtonPressed() {
guard let name = textField.text else { return }
// 4 CoreData viewContext > NSFetchRequest > Delegate (us)
GameManager.shared.createGame(name: name)
// games.append(text)
//
// let indexPath = IndexPath(row: games.count - 1, section: 0)
//
// tableView.beginUpdates()
// tableView.insertRows(at: [indexPath], with: .fade)
// tableView.endUpdates()
}
}
// MARK: - UITableView DataSource
extension DemoFetchedResultsViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath)
// 5
// cell.textLabel?.text = games[indexPath.row]
let game = fetchedResultsController.object(at: indexPath)
cell.textLabel?.text = game.name
cell.accessoryType = UITableViewCell.AccessoryType.none
return cell
}
func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
let action = UIContextualAction(style: .destructive, title: "Delete", handler: { (action, view, completionHandler) in
// 6 Deletion is now a two step process.
// self.games.remove(at: indexPath.row)
// tableView.deleteRows(at: [indexPath], with: .fade)
// 6a. Delete CoreData here
let game = self.fetchedResultsController.object(at: indexPath)
GameManager.shared.persistentContainer.viewContext.delete(game)
GameManager.shared.saveContext()
})
action.image = makeSymbolImage(systemName: "trash")
let configuration = UISwipeActionsConfiguration(actions: [action])
return configuration
}
// 7
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
let sectionInfo = fetchedResultsController.sections![section]
return sectionInfo.numberOfObjects
}
}
// 8
extension DemoFetchedResultsViewController: NSFetchedResultsControllerDelegate {
func numberOfSections(in tableView: UITableView) -> Int {
return fetchedResultsController.sections?.count ?? 0
}
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.beginUpdates() // a
}
// 6b Update table via delegate callback here.
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
switch type {
case .insert:
tableView.insertRows(at: [newIndexPath!], with: .fade) // b
case .delete:
tableView.deleteRows(at: [indexPath!], with: .fade)
case .update:
tableView.reloadRows(at: [indexPath!], with: .fade)
case .move:
tableView.moveRow(at: indexPath!, to: newIndexPath!)
default:
break
}
}
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.endUpdates() // c
}
}