我目前正在使用Xcode 6 beta 7，并决定在创建项目后我需要CoreData。我已经看过一些已经问过这个目标C的问题以及关于这个主题的观看视频，但我似乎得到了同样的错误。至于我对CoreData框架本身的使用，我很确定它是正确的，因为我创建了另一个空项目（检查了CoreData框）并遵循相同的实现，它就像一个魅力，但可能有些不对劲我是在那里做。以下是我在Swift项目中实现CoreData的步骤。
第1步：我通过“Build Phase”下的“Link Binary with Libraries”选项卡添加了CoreData框架
步骤2：然后我去了我需要实现CoreData的任何.swift文件（appDelegate.swift和现在的另一个文件）并添加了一行：
import CoreData
到顶部。
步骤3：我创建了一个名为“cData”的实体的数据列表，然后为它创建了一个名为“data.swift”的类。这是data.swift：
import UIKit
import CoreData
@objc( data )
class data: NSManagedObject {
@NSManaged var something : String
}
步骤4：我编写了代码以将数据实际保存在另一个文件中：
@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)
}
第5步：这是我相信我搞砸了的地方，虽然我错了。我在一台单独的Mac上创建了一个新项目（所以我可以将它命名为同一个东西）并检查CoreData框。然后我将整个appDelegate.swift从这个项目复制到我当前的项目中。这是我的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()
}
}
}
}
一旦调用了IBAction方法“useCoreData”，我就会崩溃并且异常表示“致命错误：在展开Optional值时意外发现nil （lldb）“并说明违规行在appDelegate.swift中：
let modelURL = NSBundle.mainBundle().URLForResource("my_app", withExtension: "momd")!
同样，当我在另一个从一开始就检查了CoreData框的项目中尝试这个相同的CoreData实现时，它就像一个魅力。我看到了类似的问题（用户得到了同样的错误），但似乎他的问题也没有解决。
答案 0 :(得分：15)
您在那里获得了nil值，因为它的主要包中不存在它所寻找的文件。
您需要将数据模型文件从您创建的其他项目复制到主项目。该文件将被称为My_App.xcdatamodeld，并且应该位于Xcode项目文件所在的文件夹中。
注意： URLForResource行正在寻找My_App.momd;该文件由Xcode在编译项目时由My_App.xcdatamodeld创建。