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，在创建项目后决定需要CoreData。我已经看了一些关于目标C的问题，同时也看了关于这个主题的视频，但我似乎也犯了同样的错误。至于我对CoreData框架本身的使用，我非常确信它是正确的，因为我创建了另一个空项目（选中了CoreData框），并遵循了相同的实现，它看起来很有魅力，但我可能也做错了什么。以下是我在Swift项目中实现CoreData所遵循的步骤。

步骤1:我通过"构建阶段"下的"链接二进制与库"选项卡添加了CoreData框架

步骤2：然后我转到任何需要实现CoreData的.swift文件（appDelegate.swift和目前的另一个文件），并添加行：

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，然后为它创建了一种名为"data.swift"的类

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

第4步：我编写了代码，实际将数据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)
    }

第五步：这是我认为我搞砸的地方，尽管我可能错了。我在一台单独的Mac上创建了一个新项目（这样我就可以用同样的名字命名它），并选中了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。这是我的应用Delegate.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()
            }
        }
    }
}

调用IBAction方法"useCoreData"后，我会出现崩溃，异常状态为"致命错误：在展开可选值时意外发现nil"（lldb）"，并声明违规行在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选中了CoreData框的项目中尝试同样的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），但他的问题似乎也没有得到解决。

Answer 1

您在那里得到一个nil值，因为它要查找的文件在您的主捆绑包中不存在。

您需要将数据模型文件从创建的其他项目复制到主项目中。该文件将被称为类似My_App.xcdatamodeld的文件，并且应该位于Xcode项目文件所在的同一文件夹中。

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