CODEWITHSUNDEEP
swiftcore-data
vaart12345
vaart12345

Reputation: 61

Could not cast value of type 'NSAsynchronousFetchResult' (0x103e13388) to 'NSArray' (0x10435cf28) Swift

I am working through a Core Data tutorial and my code throws the following error.

Could not cast value of type 'NSAsynchronousFetchResult' (0x103e13388) to 'NSArray' (0x10435cf28). 2018-12-29 22:54:17.619639+0700 demoCoreData[2670:247527] Could not cast value of type 'NSAsynchronousFetchResult' (0x103e13388) to 'NSArray' (0x10435cf28). (lldb)

My Question is:

Based on the error provided what is the reason my application is failing ?

Here's my code that won't compile:

import UIKit
import CoreData

class ViewController: UIViewController {
@IBOutlet weak var txtID: UITextField!
@IBOutlet weak var txtTen: UITextField!
@IBOutlet weak var txtTuoi: UITextField!
@IBOutlet weak var lblKetQua: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}


@IBAction func btnInsert(_ sender: Any) {
    let appDel: AppDelegate = UIApplication.shared.delegate as! AppDelegate // tạo biến để connect giữa iphone với Manage Object Context
    let context: NSManagedObjectContext = appDel.persistentContainer.viewContext //tạo biến connect với db
    //insert new Khach Hang
    let newKH = NSEntityDescription.insertNewObject(forEntityName: "KhachHang", into: context) //insert new object

    newKH.setValue(Int(txtID.text!), forKey: "id") //forKey = tên column
    newKH.setValue(txtTen.text, forKey: "tenKH")
    newKH.setValue(Int(txtTuoi.text!), forKey: "tuoiKH")

    do {
        try context.save()
        print("Insert Success")
    }catch {
        let err = error as NSError
        print("Error is: \(err)")
    }

}

@IBAction func btnShow(_ sender: Any) {
    let appDel: AppDelegate = UIApplication.shared.delegate as! AppDelegate // tạo biến để connect giữa iphone với Manage Object Context

    let context: NSManagedObjectContext = appDel.persistentContainer.viewContext // tạo biến connect với db

    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "KhachHang")// tạo biến truy vấn đến table "KhachHang"

    request.returnsObjectsAsFaults = false // có trả về những kết quả sai hay ko

    do {
        let results = try context.execute(request)
        print("Truy Van Success")

        for re in results as! [NSManagedObject] {
            print(re.value(forKey: "tenKH"))
        }

    }catch {
        let err = error as NSError
        print("Excute err: \(err)")
    }
} 
}

Here is my *.xcdatamodeld file

https://drive.google.com/open?id=18b1iJYz3jWAFkxYK2V4RrkxCTeWuR5yr

What I would really like to know, is how to investigate this on my own. Thanks in advance for any help!

Upvotes: 4

Views: 915

Answers (1)

Tom Harrington
Tom Harrington

Reputation: 70976

From your code:

    let results = try context.execute(request)

    for re in results as! [NSManagedObject] {
        print(re.value(forKey: "tenKH"))
    }

The execute method you're using returns an instance of NSPersistentStoreResult. This is an abstract class. The NSAsynchronousFetchResult mentioned in your error message is a concrete subclass of NSPersistentStoreResult.

Next, you attempt to cast this to [NSManagedObject], which is a different, unrelated class. The error you see happens because it's not possible to typecast an NSAsynchronousFetchResult to an array, because they are not related or even similar to each other.

It looks like you meant to use fetch(request) instead of execute(request), because fetch returns an array of managed objects.

What I would really like to know, is how to investigate this on my own.

I wouldn't mention it but since you asked specifically: This is something you'd resolve by looking at Apple's documentation for the classes and methods you're using. The execute method is documented to return something different from what your code expects, and the error message gives a big clue to the nature of the problem.

Upvotes: 4

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