ios - 无法在 swift 2 中更新实体

Question

我在使用 swift 2 更新实体记录时遇到问题，在我的代码中，我希望能够从选择器 View 中选择一个值，例如语言，然后将该值存储到核心数据中，但如果它在更新该值之前已存储。

我的所有代码都有效，但我的更新代码给我应用程序委托(delegate)错误:

这是我的完整代码:

import UIKit
import CoreData

class secondViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource {

    //Mark : initializing variables
    @IBOutlet var labelPassedData: UILabel!
    @IBOutlet var pickerView: UIPickerView!
    var toPass:String!

    //data source
    var languageDB = [NSManagedObject]()
    @IBOutlet weak var dbshow: UILabel!

    let managedContext = AppDelegate().managedObjectContext

    var languagePicker = ["فارسی","English","العربية"]



    override func viewDidLoad() {
        super.viewDidLoad()    
        pickerView = UIPickerView()

        pickerView.dataSource = self
        pickerView.delegate = self

        labelPassedData.text = languagePicker[0] //

        fetch("Language")
        let counter : Int = languageDB.count
        print (counter)
        let Language = languageDB[counter - 1]
        dbshow!.text = Language.valueForKey("lang") as? String

    }


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


    func numberOfComponentsInPickerView (pickerView : UIPickerView) -> Int{
        return 1
    }

    func pickerView(pickerView : UIPickerView , numberOfRowsInComponent component : Int) ->Int{
        return languagePicker.count
    }

    func pickerView(pickerView : UIPickerView, titleForRow row:Int, forComponent component : Int) -> String?
    {
        return languagePicker[row]
    }

    func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int){

        labelPassedData.text = languagePicker[row]

        self.Insert(labelPassedData!.text!) // calling save lang function


        let Language = languageDB[row]
        dbshow!.text = Language.valueForKey("lang") as? String

        self.view.endEditing(true)
    }



    func Insert(lang : String) {
        let check_empty = entityIsEmpty("Language")
        if(check_empty != true){

            let saveLanguage = NSEntityDescription.insertNewObjectForEntityForName("Language", inManagedObjectContext: managedContext)

            // add our data
            saveLanguage.setValue(lang, forKey: "lang")

            //2
            do {
                try managedContext.save()
                //3
                languageDB.append(saveLanguage)
            } catch let error as NSError  {
                print("Could not save \(error), \(error.userInfo)")
            }

        //check_empty
        }else{

            print ("update")
            let predicate = NSPredicate(format: "objectID == %@", "31")

            let fetchRequest = NSFetchRequest(entityName: "Language")
            fetchRequest.predicate = predicate

            do {
                let fetchedEntities = try self.managedContext.executeFetchRequest(fetchRequest) as! [Language]
                fetchedEntities.first?.lang = lang

                // ... Update additional properties with new values
            } catch {
                // Do something in response to error condition
            }

            do {
                try self.managedContext.save()
            } catch {
                // Do something in response to error condition
            }

        }
    }


    func fetch(entity: String){
        let langfetch = NSFetchRequest(entityName: entity)

        do{
            let results = try managedContext.executeFetchRequest(langfetch)
            languageDB = results as! [NSManagedObject]

        }catch{
            fatalError("bad things happend \(error)")
        }

    }


    func entityIsEmpty(entity: String) -> Bool
    {

        let request = NSFetchRequest(entityName: entity)

        do{
            let results = try managedContext.executeFetchRequest(request)
            languageDB = results as! [NSManagedObject]

        }catch{
            fatalError("Cant handel entity \(error)")
        }

        if languageDB.count != 0
        {
            return true
        }
        else
        {
            return false
        }


    }



}

Answer 1

大概是这一行:

let fetchRequest = NSFetchRequest(entityName: "MyEntity")

应该使用“语言”作为实体名称。我怀疑这是错误的根源。但我也认为你的谓词会导致问题——看起来你只想保存一个项目，所以不需要过滤结果——所以不需要谓词。