使用 Swift 将 CoreData 实现到现有项目中

Question

我目前正在使用 Xcode 6 beta 7，并在创建项目后决定需要 CoreData。我已经查看了一些已经针对目标 C 提出的问题以及观看有关该主题的视频，但我似乎遇到了同样的错误。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（选中了 CoreData 框）并遵循相同的实现，它就像一个魅力但可能有问题我也在那里做。下面是我在 Swift 项目中实现 CoreData 所遵循的步骤。

第 1 步：我通过“Build Phases”下的“Link Binary with Libraries”选项卡添加了 CoreData 框架

第 2 步：然后我转到需要实现 CoreData 的任何 .swift 文件（appDelegate.swift 和现在的另一个文件）并添加以下行：

import CoreData

到顶部。

第 3 步：我创建了一个包含名为“cData”的实体的数据列表，然后为其创建了一个名为“data.swift”的类。这是data.swift：

import UIKit
import CoreData

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

第 4 步：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：这是我认为我搞砸的地方，尽管我可能是错的。我在一个单独的 Mac 上创建了一个新项目（所以我可以将它命名为相同的东西）并检查了 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状态为“致命错误：在展开可选值时意外发现 nil (lldb)" 并指出违规行在 appDelegate.swift 中：

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

再次，当我在另一个项目中尝试相同的 CoreData 实现时，从一开始就选中了 CoreData 框，它就像一个魅力。我看到了一个类似的问题（用户遇到了同样的错误），但他的问题似乎也没有解决。

Answer 1

你在那里得到一个nil 值，因为它正在寻找的文件在你的主包中不存在。

您需要将数据模型文件从您创建的其他项目复制到您的主项目。该文件将被称为 My_App.xcdatamodeld 之类的名称，并且应该位于 Xcode 项目文件所在的同一文件夹中。

注意：URLForResource 行正在寻找 My_App.momd；该文件是 Xcode 在编译您的项目时从 My_App.xcdatamodeld 创建的。