I get this error : ItinerariesCodeChallenge[2594:1022206] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'An instance of NSFetchedResultsController requires a fetch request with sort descriptorsHere's my code. Really appreciate your help, I've tried everything for days now...
import UIKit
import CoreData
class MainVC: UIViewController, UITableViewDelegate, UITableViewDataSource, NSFetchedResultsControllerDelegate {
// outlets & properties:
@IBOutlet weak var tableView: UITableView!
var controller: NSFetchedResultsController<Itineraries>!
override func viewDidLoad() {
super.viewDidLoad()
tableView.delegate = self
tableView.dataSource = self
}
override func viewWillAppear(_ animated: Bool) {
attemptFetch()
tableView.reloadData()
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! CellContent
configureCell(cell: cell, indexPath: indexPath as NSIndexPath)
return cell
}
func configureCell(cell: CellContent, indexPath: NSIndexPath) {
let itinerary = controller.object(at: indexPath as IndexPath)
cell.configureCell(itineraries: itinerary)
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
if let objs = controller.fetchedObjects, objs.count > 0 {
let itinerary = objs[indexPath.row]
performSegue(withIdentifier: "toDetailsVC", sender: itinerary)
}
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "toDetailsVC" {
if let destination = segue.destination as? DetailVC {
if let itinerary = sender as? Itineraries {
destination.itineraryToEdit = itinerary
}
}
}
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
if let sections = controller.sections {
let sectionInfo = sections[section]
return sectionInfo.numberOfObjects
}
return 0
}
func numberOfSections(in tableView: UITableView) -> Int {
if let sections = controller.sections {
return sections.count
}
return 0
}
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
return 140
}
func attemptFetch() {
let fetchRequest: NSFetchRequest<Itineraries> = Itineraries.fetchRequest()
let controller = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
controller.delegate = self
self.controller = controller
do {
try controller.performFetch()
} catch {
let error = error as NSError
print("\(error)")
}
}
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.beginUpdates()
}
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.endUpdates()
}
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
switch(type) {
case.insert:
if let indexPath = newIndexPath {
tableView.insertRows(at: [indexPath], with: .fade)
}
break
case.delete:
if let indexPath = indexPath {
tableView.deleteRows(at: [indexPath], with: .fade)
}
break
case.update:
if let indexPath = indexPath {
let cell = tableView.cellForRow(at: indexPath) as! CellContent
configureCell(cell: cell, indexPath: indexPath as NSIndexPath)
}
break
case.move:
if let indexPath = indexPath {
tableView.deleteRows(at: [indexPath], with: .fade)
}
if let indexPath = newIndexPath {
tableView.insertRows(at: [indexPath], with: .fade)
}
break
}
Please read the error message carefully, it tells exactly what's wrong
An instance of NSFetchedResultsController requires a fetch request with sort descriptors.
Add at least one sort descriptor:
let fetchRequest: NSFetchRequest<Itineraries> = Itineraries.fetchRequest()
fetchRequest.sortDescriptors = [NSSortDescriptor(key: "...")]
let controller = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
Side note, not related to the issue: Remove all type casts as NSIndexPath, they are redundant.
来源：https://stackoverflow.com/questions/44748929/swift3-coredata-fetchresultscontroller