fetchedResultsController returns nil - ios

Question

Trying to create simple application to display data from Core Data to Table View. The code builds successfully - every time it loads it adds new entry, currently more than 20 - but then it crashes when trying to build the table.
Here I have ViewController:
import UIKit
import CoreData
class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
#IBOutlet weak var habitTable: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
let habitClassName:String = String(describing: Habits.self)
let habit:Habits = NSEntityDescription.insertNewObject(forEntityName: habitClassName, into: DatabaseController.getContext()) as! Habits
habit.habitsPic = ":("
habit.positive = false
habit.theHabit = "do bad"
DatabaseController.saveContext()
let fetchRequest:NSFetchRequest<Habits> = Habits.fetchRequest()
do{
let searchResults = try DatabaseController.getContext().fetch(fetchRequest)
print("number of results: \(searchResults.count)")
}
catch{
print("Error \(error)")
}
}
//CONSTRUCT TABLE VIEW
func numberOfSectionsInTableView(tableView: UITableView)-> Int {
return fetchedResultsController.sections!.count
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
guard let sections = fetchedResultsController.sections else {
fatalError("No sections in fetchedResultsController")
}
let sectionInfo = sections[section]
return sectionInfo.numberOfObjects
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath)-> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "positiveCell", for: indexPath as IndexPath)
let habit = fetchedResultsController.object(at: indexPath as IndexPath) as! Habits
cell.textLabel?.text = habit.theHabit
cell.detailTextLabel?.text = habit.habitsPic
return cell
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
//FOR DISPLAYING DATA IN TABLE
var fetchedResultsController: NSFetchedResultsController<NSFetchRequestResult>!
func initializeFetchedResultsController() {
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Habits")
let departmentSort = NSSortDescriptor(key: "theHabit", ascending: true)
let lastNameSort = NSSortDescriptor(key: "positive", ascending: true)
request.sortDescriptors = [departmentSort, lastNameSort]
let moc = DatabaseController.getContext()
fetchedResultsController = NSFetchedResultsController(fetchRequest: request, managedObjectContext: moc, sectionNameKeyPath: nil, cacheName: nil)
fetchedResultsController.delegate = (self as! NSFetchedResultsControllerDelegate)
do {
try fetchedResultsController.performFetch()
} catch {
fatalError("Failed to initialize FetchedResultsController: \(error)")
}
}
}
And DatabaseController:
import Foundation
import CoreData
class DatabaseController {
private init(){
}
class func getContext() -> NSManagedObjectContext{
return DatabaseController.persistentContainer.viewContext
}
let container = NSPersistentContainer(name: "ada")
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
return container
}()
// MARK: - Core Data Saving support
class func saveContext () {
let context = persistentContainer.viewContext
if context.hasChanges {
do {
try context.save()
} catch {
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
}
}
}
It will not build the table view, because the fetchedResultsController returns nil. I assume it is problem with "moc" variable, but what?
EDIT
error:
fatal error: unexpectedly found nil while unwrapping an Optional value
line:
guard let sections = fetchedResultsController.sections else {

Answer 1

You declare your fetched results controller as an implicitly unwrapped optional:
var fetchedResultsController: NSFetchedResultsController<NSFetchRequestResult>!
Its initial value is nil.
You also have a method called initializeFetchedResultsController that assigns a value to this property, but you never call that method. In a comment you said that you're calling it in this code:
guard let sections = fetchedResultsController.sections else {
fatalError("No sections in fetchedResultsController")
}
But that code never mentions the initializeFetchedResultsController method, and so it never calls that method.
You have an optional variable but you never assign it a value. So it never gets a value. So it's nil. This isn't a Core Data question, it's basic Swift. Properties don't get values unless you give them values, and you are not doing that.