IOS Dynamic Login

import UIKit
import CoreData

class ViewController: UIViewController {
    @IBOutlet weak var username: UITextField!
    @IBOutlet weak var password: UITextField!
    var user : UserTbl?
    var users :[UserTbl]=[]
    override func viewDidLoad() {

        super.viewDidLoad()
        let dirpath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true )
        print(dirpath[0]
    }

    @IBAction func btnLogin(_ sender: UIButton) {
        let appDel = UIApplication.shared.delegate as! AppDelegate
        let moc = appDel.persistentContainer.viewContext
        let fr = NSFetchRequest<UserTbl>(entityName: "UserTbl")

        //fetch all user
        do{
            users = try moc.fetch(fr)
        }
        catch{
            print(NSError.self)
        }

        //validate all user using for loop
        for user in users {
            if username.text == user.username && password.text == user.password{
                navigate()
            }
            else{
                print("Error")
            }
        }

    }

    func navigate(){
        let next = storyboard?.instantiateViewController(withIdentifier: "cat") as! CategoryViewController
        navigationController?.pushViewController(next, animated: true)
    }

}