CoreData, displaying saved journeys in a tableview - ios

Question

I am trying to display a list of all journeys recorded in a fitness-style app in a table view to show the distance (boolean) and date (timestamp) of each journey.
At the moment I have just created a variable to contain the Journeys from the core data file. When I print out the journeysArray, it shows 0 in the console even though there are some recorded journeys.
import UIKit
import CoreData
class SavedJourneysViewController: UITableViewController {
var journeyArray: [Journey] = []
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
print(journeyArray.count)
return journeyArray.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "JourneyItem", for: indexPath)
return cell
}

Answer 1

If Journey is your NSManagedObject subclass, you should use a NSFetchedResultsController to fetch the persisted objects.
Your SavedJourneysViewController must have a reference to the NSManagedObjectContext instance that you'll use to fetch your Journey objects. Let's assume that you have a viewContext property of type NSManagedObjectContext in your SavedJourneysViewController that's being set from the outside, wherever you initialize your SavedJourneysViewController.
You'll want to declare a fetchedResultsController in SavedJourneysViewController.
private lazy var fetchedResultsController: NSFetchedResultsController<Journey> = {
let fetchRequest: NSFetchRequest< Journey > = Journey.fetchRequest()
let sortDescriptor = NSSortDescriptor(keyPath: \Journey.date, ascending: true)
fetchRequest.sortDescriptors = [sortDescriptor]
let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: viewContext, sectionNameKeyPath: nil, cacheName: nil)
return fetchedResultsController
}()
Then perform fetch in viewDidLoad (for example) by calling try? fetchedResultsController.performFetch():
Then in numberOfRowsInSection return fetchedResultsController.sections?[section].objects?.count ?? 0:
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return fetchedResultsController.sections?[section].objects?.count ?? 0
}
Don't forget about implementing func numberOfSections(in tableView: UITableView) -> Int and returning fetchedResultsController.sections?.count ?? 0:
func numberOfSections(in tableView: UITableView) -> Int {
return fetchedResultsController.sections?.count ?? 0
}
In cellForRowAt, configure your cell with a Journey object:
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = let cell = tableView.dequeueReusableCell(withIdentifier: "JourneyItem", for: indexPath)
guard let journey = fetchedResultsController.sections?[indexPath.section].objects?[indexPath.row] as? Journey else {
return cell
}
// handle cell configuration
cell.textLabel?.text = String(journey.distance)
return cell
}
More about using NSFetchedResultsController with UITableViewController -
https://cocoacasts.com/populate-a-table-view-with-nsfetchedresultscontroller-and-swift-3
https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/CoreData/nsfetchedresultscontroller.html