Actualmente estoy usando Xcode 6 beta 7 y decidí que necesitaba CoreData después de crear mi proyecto. He examinado algunas de las preguntas que ya le piden el objetivo C junto con ver videos sobre el tema, pero parece que recibo el mismo error. En cuanto a mi uso del marco CoreData en sí, estoy bastante seguro de que es correcto, ya que creé otro proyecto vacío (con el cuadro CoreData marcado) y seguí la misma implementación y funcionó de maravilla, pero puede haber algo mal. haciendo allí también. Aquí están los pasos que seguí para implementar CoreData en mi proyecto en Swift.

Paso 1: agregué el marco CoreData a través de la pestaña "Enlace binario con bibliotecas" en "Fases de compilación"

Paso 2: luego fui a cualquiera de mis archivos .swift que necesitaría implementar CoreData (appDelegate.swift y otro archivo a partir de ahora) y agregué la línea:

import CoreData

a la cima.

Paso 3: Creé una lista de datos con una entidad llamada "cData", luego hice una clase llamada "data.swift". Aquí está data.swift:

import UIKit
import CoreData

@objc( data )
class data: NSManagedObject {
    @NSManaged var something : String
}

Paso 4: escribí el código para guardar los datos en otro archivo:

@IBAction func useCoreData(sender: AnyObject)
    {
        let AD : AppDelegate = UIApplication.sharedApplication().delegate as AppDelegate
        let ct : NSManagedObjectContext = AD.managedObjectContext!
        let ent = NSEntityDescription.entityForName( "CData", inManagedObjectContext: ct )
        var dat = data( entity: ent!, insertIntoManagedObjectContext: ct )
        dat.something = someTextField.text
        ct.save( nil )

        println(dat)
    }

Paso 5: Aquí es donde creo que me equivoqué, aunque podría estar equivocado. Creé un nuevo proyecto en una Mac separada (para poder nombrarlo igual) y marqué la casilla CoreData. Luego copié todo el appDelegate.swift de este proyecto al actual. Aquí está mi appDelegate.swift:

import UIKit
import CoreData

@UIApplicationMain

class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }

    func applicationWillResignActive(application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
    }

    func applicationDidEnterBackground(application: UIApplication) {
        // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
        // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
    }

    func applicationWillEnterForeground(application: UIApplication) {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
    }

    func applicationDidBecomeActive(application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    }

    func applicationWillTerminate(application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
        // Saves changes in the application's managed object context before the application terminates.
        self.saveContext()
    }

    // MARK: - Core Data stack

    lazy var applicationDocumentsDirectory: NSURL = {
        // The directory the application uses to store the Core Data store file. This code uses a directory named "y.Simple_Grade" in the application's documents Application Support directory.
        let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
        return urls[urls.count-1] as NSURL
        }()

    lazy var managedObjectModel: NSManagedObjectModel = {
        // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
        let modelURL = NSBundle.mainBundle().URLForResource("my_app", withExtension: "momd")!
        return NSManagedObjectModel(contentsOfURL: modelURL)
        }()

    lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator? = {
        // The persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it. This property is optional since there are legitimate error conditions that could cause the creation of the store to fail.
        // Create the coordinator and store
        var coordinator: NSPersistentStoreCoordinator? = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
        let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("my_app.sqlite")
        var error: NSError? = nil
        var failureReason = "There was an error creating or loading the application's saved data."
        if coordinator!.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil, error: &error) == nil {
            coordinator = nil
            // Report any error we got.
            let dict = NSMutableDictionary()
            dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
            dict[NSLocalizedFailureReasonErrorKey] = failureReason
            dict[NSUnderlyingErrorKey] = error
            error = NSError.errorWithDomain("YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict)
            // Replace this with code to handle the error appropriately.
            // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            NSLog("Unresolved error \(error), \(error!.userInfo)")
            abort()
        }

        return coordinator
        }()

    lazy var managedObjectContext: NSManagedObjectContext? = {
        // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to fail.
        let coordinator = self.persistentStoreCoordinator
        if coordinator == nil {
            return nil
        }
        var managedObjectContext = NSManagedObjectContext()
        managedObjectContext.persistentStoreCoordinator = coordinator
 ,       return managedObjectContext
        }()

    // MARK: - Core Data Saving support

    func saveContext () {
        if let moc = self.managedObjectContext {
            var error: NSError? = nil
            if moc.hasChanges && !moc.save(&error) {
                // Replace this implementation with code to handle the error appropriately.
                // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                NSLog("Unresolved error \(error), \(error!.userInfo)")
                abort()
            }
        }
    }
}

Una vez que se llama al método IBAction "useCoreData", aparece un bloqueo y la excepción indica "error fatal: se encontró inesperadamente nulo al desenvolver un valor Opcional (lldb)" y dice que la línea ofensiva está en appDelegate.swift:

let modelURL = NSBundle.mainBundle().URLForResource("my_app", withExtension: "momd")!

Nuevamente, cuando intento esta misma implementación de CoreData en otro proyecto que tenía la casilla CoreData marcada desde el principio, funciona de maravilla. Vi una pregunta similar como esta (el usuario estaba recibiendo el mismo error), pero tampoco parece que su problema se haya resuelto.