Difficulty configuring NSFetchedResultsController in Swift 3 - ios

Question

I'm refactoring an existing project from Swift 2 to Swift 3. Everything has been straightforward until I got to refactoring Core Data. I'm able to create managed objects and persist them in the managedObjectContext, but I'm having difficulty getting NSFetchedResultsController to work. I took a look at this post, but it's not getting me across the finish line.
After importing records from a JSON, I verify there are objects in my managedObjectContext with the following code:
func recordCount() -> Int {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let fetchRequest: NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: "MyEntity")
let count = try! context.count(for: fetchRequest)
return count
}
When I create a fetchedResultsController, I'm running into trouble. My code doesn't crash, but it doesn't return NSManagedObjects despite there being objects that match my search.
Here's how I'm creating my NSFetchedResultsController in a UIViewController.
class MyViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, NSFetchedResultsControllerDelegate {
// This is set on a prior viewController before segue.
// I've verified it's not nil
var selectedEquipmentString: String?
let managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
lazy var fetchedResultsController: NSFetchedResultsController<MyEntity> = {
// I've tried altering the syntax of the fetchRequest
// let fetchRequest: NSFetchRequest<MyEntity> = MyEntity.fetchRequest()
let fetchRequest: NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: "MyEntity")
let sortDescriptor = NSSortDescriptor(key: "generalArea", ascending: true)
fetchRequest.sortDescriptors = [sortDescriptor]
fetchRequest.predicate = NSPredicate(format: "equipmentDescription == %#", self.selectedEquipmentString!)
let frc: NSFetchedResultsController<MyEntity> = NSFetchedResultsController(fetchRequest: fetchRequest as! NSFetchRequest<MyEntity>, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: "generalArea", cacheName: nil)
frc.delegate = self
return frc
}()
// MARK: - View Lifecycle Methods (abbreviated)
override func viewDidLoad() {
super.viewDidLoad()
// I've tried moving this call to viewWillAppear and viewDidAppear without success
fetchObjectsFromManagedObjectContext()
}
// MARK: - Core Data Methods (abbreviated)
func fetchObjectsFromManagedObjectContext() {
do {
try fetchedResultsController.performFetch()
} catch {
print("error: \(error)")
return
}
print ("There are \(fetchedResultsController.fetchedObjects!.count) returned from fetchObjectsFromManagedObjectContext")
}
}
This code doesn't crash, but it doesn't return any records from a fetchRequest. I was able to force a crash with a typo in the predicate, but without a typo there are no objects returned despite objects that match the predicate.
I welcome any suggestions re: where my mistake is. I rest assured knowing it will be a startlingly silly oversight on my part. Thank you for reading.

Answer 1

Your NSFetchRequest should have a type NSFetchRequest<MyEntity>, but you specify NSFetchRequest<NSFetchRequestResult>. Try changing this and let me know if it helps or not

Answer 2

please check below code for NSFetchedResultsController swift 3..
override func viewDidLoad() {
super.viewDidLoad()
do {
try self.fetchedResultsController.performFetch()
} catch {
let fetchError = error as NSError
print("Unable to Perform Fetch Request")
print("\(fetchError), \(fetchError.localizedDescription)")
}
}
// MARK: - NSFetchedResultsController
fileprivate lazy var fetchedResultsController: NSFetchedResultsController<UserExistenceOnXMPPCD> = {
let fetchRequest = NSFetchRequest<UserExistenceOnXMPPCD>(entityName: "UserExistenceOnXMPPCD")
fetchRequest.sortDescriptors = [
NSSortDescriptor(key: "name", ascending: true)]
let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext:CoreDataController.sharedInstance.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
try! fetchedResultsController.performFetch()
fetchedResultsController.delegate = self
if let quotes = fetchedResultsController.fetchedObjects {
if quotes.count > 0 {
print(quotes.count)
}
}
return fetchedResultsController
}()
// MARK: - NSFetchedResultsController delegate methods
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.beginUpdates()
}
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.reloadData()
}