Authentication error/ purple warning when trying to segue after validating data from API - swift

Question

I have created a POST request which validates if the username and password are correct through a StatusCode: 0 that comes from the response of the POST request if the data are correct, At the signInViewController class I have created the button signInSegueToDashboard which when pressed must validate the data and if the data are valid then the user will be logged in without any problem.
The button sender at signInViewController:
#IBAction func signInSegueToDashboard(_ sender: Any) {
APICallerPOST.shared.signInToAccount(username: emailTextField.text!, password: passwordTextField.text!) { (result, error) in
if let result = result {
if result.StatusCode == 0 {
guard let mainTabBarController = self.storyboard?.instantiateViewController(withIdentifier: "mainTabBarController") else {
return
}
Timer.scheduledTimer(withTimeInterval: 1, repeats: false) {_ in
mainTabBarController.modalPresentationStyle = .custom
self.present(mainTabBarController, animated: true, completion: nil)
}
}else if result.StatusCode == 5 {
print("error: \(error!.localizedDescription)")
}
}
}
}
When i press the button after typing the correct data it just does nothing and just shows a purple warning that is saying to put it on Main thread, When i did put on main thread the segue part then it doesn't validate the data at all instead it just logs you in without any validation.
the POST request from APICallerPOST class:
func signInToAccount(username: String, password: String, completion: #escaping (SignInResponse?, Error?) -> Void) {
//declare parameter as a dictionary which contains string as key and value combination.
let parameters = ["User": username, "Password": password]
//create the url with NSURL
let url = URL(string: "https://censoredurl/Signin")!
//create the session object
let session = URLSession.shared
//now create the Request object using the url object
var request = URLRequest(url: url)
request.httpMethod = "POST" //set http method as POST
do {
request.httpBody = try JSONSerialization.data(withJSONObject: parameters, options: .prettyPrinted) // pass dictionary to data object and set it as request body
} catch let error {
print(error.localizedDescription)
completion(nil, error)
}
//HTTP Headers
request.addValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")
request.addValue("application/json; charset=utf-8", forHTTPHeaderField: "Accept")
//create dataTask using the session object to send data to the server
let task = session.dataTask(with: request, completionHandler: { data, response, error in
guard error == nil else {
completion(nil, error)
return
}
guard let data = data else {
completion(nil, NSError(domain: "dataNilError", code: -100001, userInfo: nil))
return
}
do {
//create json object from data
let decoder = JSONDecoder()
guard let json = try? decoder.decode(SignInResponse.self, from: data) else {
completion(nil, NSError(domain: "invalidJSONTypeError", code: -100009, userInfo: nil))
return
}
print(json)
completion(json, nil)
} catch let error {
print(error.localizedDescription)
completion(nil, error)
}
})
task.resume()
}
Confused a lot.

Answer 1

The dataTask is asynchronous, and so is the code it runs in the completion handler. However all updates to UI need to be performed on the main thread, and so the parts of the completion handler that update the UI need to be pushed back onto the main thread.
In your case you could do it like this:
if result.StatusCode == 0 {
DispatchQueue.main.async {
guard let mainTabBarController = self.storyboard?.instantiateViewController(withIdentifier: "mainTabBarController")
else {
return
}
Timer.scheduledTimer(withTimeInterval: 1, repeats: false) {_ in
mainTabBarController.modalPresentationStyle = .custom
self.present(mainTabBarController, animated: true, completion: nil)
}
}
// ...
However it seems you are trying to use the Timer to delay presentation of the viewController, and there is a better way of doing this than using the Timer. You can use a delayed execution with DispatchQueue's asyncAfter(deadline:qos:flags:execute:) method:
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
// do your UI work
}