Proper use of DispatchQueue in swift login - swift

Question

Im not using properly DispatchQueue function since I have to click 2-3 times in order to change screen, since the data dont load on time. I tried couple of positions in the code but Im always getting the same result.
What is a proper use?
Here is my code:
func startLogin() {
userNameData = userName.text!.trimmingCharacters(in: .whitespacesAndNewlines)
passwordData = password.text!.trimmingCharacters(in: .whitespacesAndNewlines)
if userNameData == "" || passwordData == "" { return } else {
let parameters = "{\n\t\"user\": \"\(userNameData)\",\n\t\"password\": \"\(passwordData)\"\n}"
let postData = parameters.data(using: .utf8)
var request = URLRequest(url: URL(string: "https://someurl.io:18999/salesAPI/login")!,timeoutInterval: Double.infinity)
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpMethod = "POST"
request.httpBody = postData
let task = URLSession.shared.dataTask(with: request) { data, response, error in
guard let data = data else {
print(String(describing: error))
print("User no encontrado!")
return
}
print(String(data: data, encoding: .utf8)!)
// semaphore.signal()
let decoder = JSONDecoder()
do {
let jsonPetitions = try decoder.decode(Token.self, from: data)
token = jsonPetitions.access_token
let defaults = UserDefaults.standard
defaults.set(true, forKey: "didLogin")
defaults.set(userNameData, forKey: "userNameData")
defaults.set(passwordData, forKey: "passwordData")
defaults.set(token, forKey: "enterKey")
}
catch {
print("No Json output!!")
return
}
}
func changeScreen() {
// performSegue(withIdentifier: "switchScreens", sender: nil)
let homeViewController = self.storyboard?.instantiateViewController(identifier: Constance.Storyboard.homeViewController) as? HomeViewController
self.view.window?.rootViewController = homeViewController
self.view.window?.makeKeyAndVisible()
}
dispatchGroup.enter()
task.resume()
self.dispatchGroup.leave()
dispatchGroup.notify(queue: DispatchQueue.main) {
if token == "" {
self.errorLabel.alpha = 0.5
self.errorLabel.text = "Algun dato esta mal"
self.errorLabel.textColor = UIColor.red
print ("No Token! User or the pass is wrong")
} else {
changeScreen()
}
}
} // end User Login
}
The code is just part of it but all the important part are there

Answer 1

The dispatch group isn’t used correctly. But rather than trying to fix that, we should just remove it, as it’s unnecessary. Just move the code inside the notify block into the dataTask closure, after you parse the data.
For example:
func startLogin() {
userNameData = userName.text!.trimmingCharacters(in: .whitespacesAndNewlines)
passwordData = password.text!.trimmingCharacters(in: .whitespacesAndNewlines)
if userNameData == "" || passwordData == "" { return }
let parameters = ["user": userNameData, "password": passwordData]
var request = URLRequest(url: URL(string: "https://someurl.io:18999/salesAPI/login")!,timeoutInterval: Double.infinity)
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpMethod = "POST"
request.httpBody = try! JSONEncoder().encode(parameters)
let task = URLSession.shared.dataTask(with: request) { data, response, error in
guard let data = data else {
print(String(describing: error))
print("User no encontrado!")
return
}
let decoder = JSONDecoder()
do {
let jsonPetitions = try decoder.decode(Token.self, from: data)
token = jsonPetitions.access_token
let defaults = UserDefaults.standard
defaults.set(true, forKey: "didLogin")
defaults.set(userNameData, forKey: "userNameData")
defaults.set(passwordData, forKey: "passwordData")
defaults.set(token, forKey: "enterKey")
DispatchQueue.main.async {
if token == "" {
self.errorLabel.alpha = 0.5
self.errorLabel.text = "Algun dato esta mal"
self.errorLabel.textColor = UIColor.red
print ("No Token! User or the pass is wrong")
} else {
self.changeScreen()
}
}
} catch {
print("No Json output!!")
return
}
}
task.resume()
}
func changeScreen() {
// performSegue(withIdentifier: "switchScreens", sender: nil)
let homeViewController = self.storyboard?.instantiateViewController(identifier: Constance.Storyboard.homeViewController) as? HomeViewController
self.view.window?.rootViewController = homeViewController
self.view.window?.makeKeyAndVisible()
}