Log in user through json and display the application

I am currently learning swift 4 and would like to ask you to correct my code. (I would like to have a pattern for learning the "beautiful code").

My code gets data from the server in JSON format and creates a loggedUser object. Then I open the tabbed view controller with the correct application.

I'm trying to write an MVC compliant code.

My user login code:

login.swift

import UIKit

class LoginViewController: UIViewController {

    // outlets
    @IBOutlet weak var textFieldLogin: UITextField!
    @IBOutlet weak var textFieldPassword: UITextField!
    let cms = Connect()


    @IBAction func btnLoginPressed(_ sender: Any) {
        if self.textFieldLogin.text?.isEmpty ?? true || self.textFieldPassword.text?.isEmpty ?? true  {
            self.errorLoginMessage(txt: "Uzupełnij wszystkie pola!!", title: "Błąd")
        } else {
            cms.checkUsersLogin(login: self.textFieldLogin.text, password: self.textFieldPassword.text, callback: { (data, error) in
                if error == nil{
                    if let dane = data {
                        do {
                            let decoder = JSONDecoder()
                            loggedUser = try decoder.decode(LoginUser.self, from: data!)

                            if ((loggedUser?.id ) == nil) {
                                let json = try? JSONSerialization.jsonObject(with: data!, options: [])

                                if let dictionary = json as? [String: Any] {
                                    if let komunikat = dictionary["komunikat"] as? String, let title = dictionary["error"] as? String {
                                        DispatchQueue.main.async {
                                            self.errorLoginMessage(txt: komunikat, title: title)
                                        }
                                    }
                                } else {
                                    DispatchQueue.main.async {
                                        self.errorLoginMessage(txt: "Podany login lub hasło jest błędny!!", title: "Błąd")
                                    }
                                }
                            } else {
                                DispatchQueue.main.async {
                                    dump(loggedUser)
                                    self.performSegue(withIdentifier: "toLoginUser", sender: self)
                                }
                            }
                        }
                        catch {
                            print("Error in decoder")
                        }
                    } else {
                        print("Error 103: \(data)")
                    }
                } else {
                    print("Error 104: \(error)")
                }


            })
        }
    }




    override func viewDidLoad() {
        super.viewDidLoad()

    }

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

    override func prepare(for segue: UIStoryboardSegue, sender: Any?){
        if segue.identifier == "toLoginUser" {


        }
    }

    func errorLoginMessage(txt: String, title: String){
        let ac = UIAlertController(title: title, message: nil, preferredStyle: .alert)
        let alertController = UIAlertController(title: title, message: txt, preferredStyle: .alert)
        alertController.addAction(UIAlertAction(title: "Ok", style: .cancel, handler: { (action: UIAlertAction!) in

        }))
        self.present(alertController, animated: true, completion: nil)
    }

    override var prefersStatusBarHidden: Bool {
        return true
    }
}

My class for connecting to the server and handling requests:

connect.swift

import Foundation

public struct Connect {
    let serverAdress = "http://myserwer.pl/"
    typealias Answer = (Data?, Error?) -> Void


    func getJsonFromServer(parameters: String, responseRequest: @escaping Answer) {
        guard let Url = URL(string: self.serverAdress + "kartyEndpoint.qbpage" + parameters) else { return }
        URLSession.shared.dataTask(with: Url) { (data, response, error) in
            if error == nil {
                guard let data = data else {
                    print("Error 100:  \(error)")
                    responseRequest(nil, error)
                    return
                }
                print("R>" + self.serverAdress + "kartyEndpoint.qbpage" + parameters)
                do {
                    responseRequest(data, nil)

                } catch let err {
                    print("Error 101: ", err)
                    responseRequest(nil, err)
                }
            } else{
                print("Error 102: Problem with download data")
            }
        }.resume()
    }

    func checkUsersLogin(login: String?, password: String?, callback: @escaping Answer) {
        getJsonFromServer(parameters: "?action=LOGOWANIE&login=\(login!)&password=\(password!)", responseRequest: callback)
    }

}