使用Swift将CoreData实施到现有项目中

Question

我当前正在使用Xcode 6 beta
7，并在创建项目后决定需要CoreData。我已经看过一些已经问到目标C的问题，同时还观看了有关该主题的视频，但我似乎遇到了同样的错误。至于我对CoreData框架本身的用法，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），并且遵循相同的实现，它像一个魅力一样起作用，但是我可能有问题也在那里做。因此，这是我在Swift的项目中实现CoreData的步骤。

步骤1：我通过“ Build Phases”下的“ Link Binary with Libraries”选项卡添加了CoreDatahtml" target="_blank">框架。

步骤2：然后，我转到需要实现CoreData的任何.swift文件（appDelegate.swift和到目前为止的另一个文件），并添加以下行：

import CoreData

到顶部。

步骤3：我创建了一个带有名为“ 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
}

步骤4：我编写了将数据实际保存到另一个文件中的代码：

@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：尽管我可能错了，但我还是在这里搞砸了。我在单独的Mac上创建了一个新项目（因此我可以使用相同的名称）并选中了CoreData框。然后，我将整个appDelegate.swift从该项目复制到当前项目。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()
            }
        }
    }
}

调用IBAction方法“
useCoreData”后，出现崩溃，异常状态为“致命错误：在展开可选值（lldb）时意外发现nil”，并指出有问题的行位于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框的项目中尝试使用相同的CoreData实现时，它就像一个超级按钮。我看到了类似的问题（用户遇到相同的错误），但似乎他的问题也未得到解决。

Answer 1

您在那里获得了nil价值，因为要查找的文件在主捆绑包中不存在。

您需要将数据模型文件从创建的另一个项目复制到主项目。该文件的名称类似于My_App.xcdatamodeld，应位于Xcode项目文件所在的文件夹中。

注意：
该URLForResource行正在寻找My_App.momd；该文件是Xcode从My_App.xcdatamodeld编译项目时创建的。