ios - 为什么我得到 "Swift Dynamic Cast Failed"？ :/

Question

我想知道是否有人可以向我解释有关编程的“cast”或“casting”的概念，并帮助我解决在尝试执行此代码时出现“Swift dynamic cast failed”的问题:

import UIKit
import CoreData

class vcMain: UIViewController {
    
    @IBOutlet var txtUsername: UITextField!
    @IBOutlet var txtPassword: UITextField!
    
    @IBAction func btnSave(){
        //println("Save button pressed \(txtUsername.text)")//Adds the text written, in the console
        var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)
        var context:NSManagedObjectContext = appDel.managedObjectContext
        
        var newUser = NSEntityDescription.insertNewObjectForEntityForName("Users", inManagedObjectContext: context) as NSManagedObjectContext
        newUser.setValue("Test Username", forKey: "username")
        newUser.setValue("Test Password", forKey: "password")
        
        context.save(nil)
        
        println(newUser)
        println("Object Saved.")
        
        
    }
    
    @IBAction func btnLoad(){
        //println("Load button pressed \(txtPassword.text)")
    }

    override func viewDidLoad() {
        super.viewDidLoad()

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

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

我正在关注 YouTube 上的教程，但无法弄清楚为什么它对我不起作用!

Answer 1

这一行看起来不对:

var newUser = NSEntityDescription.insertNewObjectForEntityForName("Users", inManagedObjectContext: context) as NSManagedObjectContext

当您可能打算转换为 NSManagedObject 时，您正在转换为 NSManagedObjectContext，因此该行应为:

var newUser = NSEntityDescription.insertNewObjectForEntityForName("Users", inManagedObjectContext: context) as NSManagedObject