Assign network response sooner - ios

Question

I'm developing an app that relies on a web service backend. I have a separate class API to handle all network activities and send the data to the relevant view controllers.
I have a NSURLSession.dataTaskWithRequest() which sends my data via POST to my API and returns a response. I figured it would be best to have a single variable networkResponse in my API class with a getter and setter as I'll only ever need one response at a time.
In my ViewController, I have a login form which makes a request to the API and will log the user in depending on the response. If the credentials are incorrect, it returns the response in a UIAlertController.
On testing incorrect credentials, I've found that the response is not getting called in time for the AlertController, so it just shows a blank message. If I dismiss it and click login again straight away, It shows the response. How would I go about getting it to display sooner?
login function:
class func login (username: String, password: String) {
config.HTTPAdditionalHeaders = ["Authorization" : authorization]
let url : NSURL = NSURL(string: "\(root)PHP/login.php")!
let request = NSMutableURLRequest(URL: url)
var returnString : NSString = ""
request.HTTPMethod = "POST"
let postString = "username=\(username)&password=\(password)"
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
var networkTask = mySession.dataTaskWithRequest(request) {
data, response, error in
var err : NSError?
dispatch_async(dispatch_get_main_queue()) {
/* Setting response variable here */
self.setNetworkResponse(NSString(data: data, encoding: NSUTF8StringEncoding)!)
}
}
networkTask.resume()
}
calling API:
#IBAction func login(sender: AnyObject) {
if !txtUsername.text.isEmpty || !txtPassword.text.isEmpty {
API.login(txtUsername.text, password: txtPassword.text)
Alert:
override func shouldPerformSegueWithIdentifier(identifier: String?, sender: AnyObject?) -> Bool {
if identifier == "segueLogin" {
if API.getNetworkResponse() !== "true" {
var alert = UIAlertController(title: "Message", message: API.getNetworkResponse() as String, preferredStyle: .Alert)

Answer 1

While its probably not the most ideal solution, I've managed to fix the problem by setting a delay, using dispatch_after in the shouldPerformSegueWithIdentifier to delay the alert by about 5 seconds. The message appears first time now which is what I'm looking for.