Question

我收到一个名为“+ entityForName的错误：nil不是一个合法的NSManagedObjectContext参数，用于搜索实体名称'Person”。实体的名称是Person，实体名称是设置为字符串的名称。这样做的全部意义在于可以为用户添加用户名，并将其保存为核心数据。有什么方法可以解决这个问题？ appdelegate类也在代码中

class TableViewUsernameViewController: UIViewController {

@IBOutlet weak var tableView: UITableView!

var people: [NSManagedObject] = []

override func viewDidLoad() {
    super.viewDidLoad()
    title = "The List"
    tableView.register(UITableViewCell.self, forCellReuseIdentifier: "Cell")

    // Do any additional setup after loading the view.
}


@IBAction func addName(_ sender: Any) {
    let alert = UIAlertController(title: "New Name",
                                  message: "Add a new name",
                                  preferredStyle: .alert)

    let saveAction = UIAlertAction(title: "Save", style: .default) {
        [unowned self] action in


        guard let textField = alert.textFields?.first,
            let nameToSave = textField.text else {
                return
        }

        self.save(name: nameToSave)
        self.tableView.reloadData()
    }


    let cancelAction = UIAlertAction(title: "Cancel",
                                     style: .default)

    alert.addTextField()

    alert.addAction(saveAction)
    alert.addAction(cancelAction)

    present(alert, animated: true)
}

func save(name: String) {

    guard let appDelegate =
        UIApplication.shared.delegate as? AppDelegate else {
            return
    }

    // 1
    let managedContext =
        appDelegate.persistentContainer.viewContext

    // 2
    let entity =
        NSEntityDescription.entity(forEntityName: "Person",
                                   in: managedContext)!

    let person = NSManagedObject(entity: entity,
                                 insertInto: managedContext)

    // 3
    person.setValue(name, forKeyPath: "name")

    // 4
    do {
        try managedContext.save()
        people.append(person)
    } catch let error as NSError {
        print("Could not save. \(error), \(error.userInfo)")
    }
}

}

// MARK: - UITableViewDataSource
extension TableViewUsernameViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView,
               numberOfRowsInSection section: Int) -> Int {
    return people.count
}

func tableView(_ tableView: UITableView,
               cellForRowAt indexPath: IndexPath)
    -> UITableViewCell {

        let person = people[indexPath.row]
        let cell =
            tableView.dequeueReusableCell(withIdentifier: "Cell",
                                          for: indexPath)
        cell.textLabel?.text =
            person.value(forKeyPath: "name") as? String
        return cell
}

}

  @UIApplicationMain
  class AppDelegate: UIResponder, UIApplicationDelegate {

var window: UIWindow?


func application(_ application: UIApplication, 
didFinishLaunchingWithOptions launchOptions: 
[UIApplicationLaunchOptionsKey: Any]?) -> 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 
   invalidate graphics rendering callbacks. 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 persistentContainer: NSPersistentContainer = {
    /*
     The persistent container for the application. This implementation
     creates and returns a container, having loaded 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.
     */
    let container = NSPersistentContainer(name: "QuizFinal")
    container.loadPersistentStores(completionHandler: { 
(storeDescription, error) in
        if let error = error as NSError? {
            // Replace this implementation with code to handle the 
error appropriately.
            // fatalError() 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.

            /*
             Typical reasons for an error here include:
             * The parent directory does not exist, cannot be created, 
 or disallows writing.
             * The persistent store is not accessible, due to 
 permissions or data protection when the device is locked.
             * The device is out of space.
             * The store could not be migrated to the current model 
 version.
             Check the error message to determine what the actual 
 problem was.
             */
            fatalError("Unresolved error \(error), \(error.userInfo)")
        }
    })
    return container
}()

// MARK: - Core Data Saving support

func saveContext () {
    let context = persistentContainer.viewContext
    if context.hasChanges {
        do {
            try context.save()
        } catch {
            // Replace this implementation with code to handle the 
error appropriately.
            // fatalError() 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
            fatalError("Unresolved error \(nserror), \
(nserror.userInfo)")
        }
    }
}

}
//short-cut to access App Delegate
let ad = UIApplication.shared.delegate as! AppDelegate
let context = ad.persistentContainer.viewContext

Answer 1

我最近遇到此错误，并发现该模块是否已设置为“当前产品模块”。而不是默认的＆＃39; Global＆＃39;问题解决了。

更改实体的模块：

选择它。
选择其属性。
转到课程部分。
点击＆＃39;模块＆＃39;下拉菜单。
选择＆＃39;当前产品模块＆＃39;

Answer 2

我认为你正在使用Ray的网站（https://www.raywenderlich.com/）。代码几乎是一个副本。我有同样的问题，令人困惑。

我检查了核心数据模型：选择（FILE.xcdatamodelid），其中FILE是项目的名称。在某个地方，我破坏了模型。只需添加一个实体，将其重命名为Person，添加名为name的属性，使用String类型。重建并运行。

实体名称为nil的核心数据实体

2 个答案: