将iOS Core Data添加到现有项目 – 解包可选值时发生错误

我试图将CoreData添加到现有的项目。 所以,我复制了一个新项目的数据模型(SWS.xcdatamodel)和AppDelegate文件。 然后我改变了AppDelegate方法中的项目名称和数据模型名称

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 inactive 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:. } // 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 "at.meinhard-kissich.SWSCore" 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("SWS", 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("SWS.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() } } } } 

之后,我试图写一个新的数据集到数据库

  let appDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate) let managedContext = appDelegate.managedObjectContext let entity = (NSEntityDescription.insertNewObjectForEntityForName("WeatherData", inManagedObjectContext: managedContext)) as NSManagedObject entity.setValue(32, forKey: "id") do { try managedContext.save() } catch let error as NSError { print("Could not save \(error), \(error.userInfo)") } print("obj saved") 

不幸的是,我总是得到以下错误:

 fatal error: unexpectedly found nil while unwrapping an Optional value 

在这一行:

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

问题在哪里?

  • 谢谢!

问题在哪里?

这很简单:你强制解包NSBundle.mainBundle().URLForResource("SWS", withExtension: "momd")返回的可选值NSBundle.mainBundle().URLForResource("SWS", withExtension: "momd") ! ,这意味着如果该值不存在,应用程序将会崩溃。 事实上,这里的问题是,NSBundle无法find您的资源。

您试图强制展开可选值,这是不正确的方式,因为它是可选的,它可能包含或不包含任何内容。 当你将强制尝试使用它,如果它包含nil那么这就是你将得到的回应。

所以正确的方法是通过首先检查是否包含某些东西来安全地打开可选值。 你可以通过使用if语句轻松做到这一点。