Atualmente, estou usando o Xcode 6 beta 7 e decidi que precisava do CoreData depois de criar meu projeto. Analisei algumas das perguntas que já pedem esse objetivo C, além de assistir a vídeos sobre o assunto, mas parece que estou recebendo o mesmo erro. Quanto ao meu uso da estrutura CoreData, tenho certeza de que está correta, pois criei outro projeto vazio (com a caixa CoreData marcada) e segui a mesma implementação e funcionou como um encanto, mas pode haver algo errado. fazendo lá também. Então, aqui estão as etapas que segui para implementar o CoreData no meu projeto no Swift.

Etapa 1: adicionei a estrutura CoreData na guia "Vincular binário com bibliotecas" em "Fases de construção"

Etapa 2: fui a qualquer um dos meus arquivos .swift que precisariam implementar o CoreData (appDelegate.swift e um outro arquivo a partir de agora) e adicionei a linha:

import CoreData

para o topo.

Etapa 3: criei uma lista de dados com uma entidade chamada "cData" e criei uma classe para ela chamada "data.swift". Aqui está data.swift:

import UIKit
import CoreData

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

Etapa 4: escrevi o código para salvar os dados em outro arquivo:

@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)
    }

Passo 5: Aqui é onde eu acredito que errei, embora eu possa estar errado. Criei um novo projeto em um Mac separado (para poder nomear a mesma coisa) e marquei a caixa CoreData. Em seguida, copiei todo o appDelegate.swift deste projeto para o meu atual. Aqui está o meu 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()
            }
        }
    }
}

Depois que o método IBAction "useCoreData" é chamado, recebo uma falha e a exceção declara "erro fatal: inesperadamente encontrado nulo ao desembrulhar um valor opcional (lldb)" e informa que a linha incorreta está em appDelegate.swift:

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

Novamente, quando tento a mesma implementação CoreData em outro projeto que teve a caixa CoreData marcada desde o início, ela funciona como um encanto. Vi uma pergunta semelhante como esta (o usuário estava recebendo o mesmo erro), mas também não parece que seu problema foi resolvido.