NSManagedObject错误

Question

我现在已经开始学习iOS的核心数据了。我目前正在获得致命错误:在下面的代码行中展开可选值时意外地发现为零。我一直在关注youtube和其他几个地方的讲座，也看过他们的代码，但不知道错误背后的原因。如果有人能为我提供一个概述，这将是非常有帮助的。目前，在我的代码中，我只是从实体分配值，没有抓取。

应用程序代表：

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

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("ActivityMonitor", withExtension: "momd")!
    return NSManagedObjectModel(contentsOfURL: modelURL)!
}()

lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator = {
    // The persistent store coordinator for the application. This implementation creates and returns 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
    let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
    let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("SingleViewCoreData.sqlite")
    var failureReason = "There was an error creating or loading the application's saved data."
    do {
        try coordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil)
    } catch {
        // Report any error we got.
        var dict = [String: AnyObject]()
        dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
        dict[NSLocalizedFailureReasonErrorKey] = failureReason

        dict[NSUnderlyingErrorKey] = error as NSError
        let wrappedError = NSError(domain: "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 \(wrappedError), \(wrappedError.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
    var managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
    managedObjectContext.persistentStoreCoordinator = coordinator
    return managedObjectContext
}()

// MARK: - Core Data Saving support

func saveContext () {
    if managedObjectContext.hasChanges {
        do {
            try managedObjectContext.save()
        } catch {
            // 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.
            let nserror = error as NSError
            NSLog("Unresolved error \(nserror), \(nserror.userInfo)")
            abort()
        }
    }
}

}

ViewController:

    @IBAction func cofirmLogin(sender: UIButton) {
    let oct = ((UIApplication.sharedApplication().delegate as? AppDelegate)?.managedObjectContext)
    var userNameValue = NSEntityDescription.insertNewObjectForEntityForName("LoginInformation", inManagedObjectContext: oct!) as! LoginInformation
    userNameValue.loginUserName = loginUserName.text!
    userNameValue.loginPin =  Int(loginPin.text!)!

    userNameValue = loginInfo
    saveContext(oct!)
}

func saveContext (context : NSManagedObjectContext) {
    if context.hasChanges {
        do {
            try context.save()
        } catch {
            let nserror = error as NSError
            NSLog("Unresolved error \(nserror), \(nserror.userInfo)")
        }
    }
}
}

Answer 1

也许有些东西没有像预期的那样与惰性变量一起工作。您可以像这样重构托管对象上下文。

var managedObjectContext: NSManagedObjectContext {
    get {

        if _managedObjectContext == nil {
            let coordinator = self.persistentStoreCoordinator
            let moc = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
            moc.persistentStoreCoordinator = coordinator
            _managedObjectContext = moc
        }
        return _managedObjectContext!
    }
}
var _rootContext: NSManagedObjectContext?

另外，确保按预期返回应用程序委托(可能将其分解为几行并签入调试器)。