How to call a protocol from an extension before changing screens - swift

Question

I need to get a value from an extension before i click on a button that goes to another screen, how can i do that?
This is the IBAction inside viewController. When i click it makes a request to an API then send a value to global variable on the second screen:
#IBAction func enter(_ sender: UIButton) {
if let login = loginTextfield.text, let password = passwordTextfield.text {
loginManager.performLoginRequest(login, password)
resultsViewController.receivedToken = token
navigationController?.pushViewController(resultsViewController, animated: true)
}
}
extension LoginViewController: LoginManagerDelegate {
func didUpdateLogin(with login: LoginModel) -> (Bool, String) {
success = login.success
token = login.token
return (success, token)
}
}
Manager:
import Foundation
protocol LoginManagerDelegate {
func didUpdateLogin(with login: LoginModel) -> (Bool, String)
}
struct LoginManager {
var delegate: LoginManagerDelegate?
func performLoginRequest(_ login: String, _ password: String) {
let url = URL(string: "https://private-anon-1a0df64d9c-ibmfc.apiary-mock.com/login")!
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpBody = """
{\n "username": "\(login)",\n "password": "\(password)"\n}
""".data(using: .utf8)
let task = URLSession.shared.dataTask(with: request) { data, response, error in
if let response = response {
print(response)
if let data = data, let body = String(data: data, encoding: .utf8) {
print(body)
if let login = self.parseJSON(loginData: data) {
self.delegate?.didUpdateLogin(with: login)
}
}
} else {
print(error ?? "Unknown error")
}
}
task.resume()
}
func parseJSON(loginData: Data) -> LoginModel? {
let decoder = JSONDecoder()
do {
let decodedData = try decoder.decode(LoginData.self, from: loginData)
let success = decodedData.success
let token = decodedData.data.token
let login = LoginModel(success: success, token: token)
return login
} catch {
print(error.localizedDescription)
return nil
}
}
}
My problem is, this extension is just being called after i click the button. This way resultsViewController.receivedToken is not getting the value from token.
So, how can i call didUpdateLogin (to pass it values to success and token) before clicking on the IBAction?

Answer 1

THe reason for this behaviour is the background thread you are using:
(1) You call loginManager.performLoginRequest(login, password) which then starts a background thread to actually work on that request.
(2) In the meantime your code continues to run, executing resultsViewController.receivedToken = token.
(3) Since (1) is not done yet, your token is still nil (or an old token).
One of many possible solutions:
Add a block to the parameters of performLoginRequest in which you call
resultsViewController.receivedToken = token
navigationController?.pushViewController(resultsViewController, animated: true)
This way you make sure that code is only called after(!) the login was successful because you wait for it. In the meantime you could show a loading spinner or something similar. Login is a task where a user simply has to wait, there is usually (depending on the app) no way around it.
The code could look something like this in the end:
loginManager.performLoginRequest(login, password) {
resultsViewController.receivedToken = token
navigationController?.pushViewController(resultsViewController, animated: true)
}
whereas your LoginManager would have a method like
func performLoginRequest(_ login: String,
_ password: String,
completion: #escaping () -> Void)
which is then used later in your Dispatch:
DispatchQueue.main.async {
let loginVC = LoginViewController()
loginVC.didUpdateLogin(login: login)
completion()
}