Can't refresh UI after async call - ios

Question

What I want to do: I have a login screen, the user fill the username and password, and then it press the login button. An async call to the server is done to check if user is registered and password is okay, and if yes (async function set a bool to yes) then do a segue to the next view controller. Simple as that, I've tried many ways but with always the same problem, the main thread runs the shouldPerformSegueWithIdentifier method, do the async call and check the global bool var (false by default) before the background thread has updated it, so the segue is not performed because the global variable is set to true AFTER. Only if I use sleep(1) the UI is refreshed but I don't want to use this. Is there a way to do this without sleep?? Every method I run has a completion handler.
I don't know how to sync the main with the background thread. I've read it's posible to update UI from async call so this should be posible. I've been looking questions for a while and tried lot of snippets, and still haven't found a solution for my problem.
This is the code I have so far:
override func shouldPerformSegueWithIdentifier(identifier: String, sender: AnyObject?) -> Bool {
let apiCall = webApi()
dispatch_async(dispatch_get_main_queue()) {
apiCall.callCheckIsUserLogged(nil, password : self.passwordField.text, email: self.mailField.text){ (ok) in
}
}
//sleep(1) if I uncomment this, my method works because it will return true
return userIsLogged
}
apiCall.callCheckIsUserLogged() :
typealias successClosure = (success : Bool) -> Void
//Make a call to check if the user exist, server returns json with success or failure
func callCheckIsUserLogged(username: String?, password : String?, email: String?,completed : successClosure){
userApiCallUrl = "http://apiurl.com/users/login"
let call = asyncCallClass()
call.doAsyncCallWithParams(userApiCallUrl, calltype: "POST", username: username, pass: password, mail: email){ (success) in
completed(success: true)
}
}
call.doAsyncCallWithParams() code:
internal typealias completion = (success : Bool) -> Void
private var flagCompletion : Bool = false
//Handle async class with this method
//var callType is aditioned everytime an arg is not passed nil.
//callType == 3 it is a call to check if user is logged
//callType == 2 is a call to register a new user
func doAsyncCallWithParams(url : String, calltype : String, username : String?, pass : String?, mail : String?, completed : completion){
var callType : Int = 0
//Set Async Url
setUrl(url)
//Set Post Params
if let user : String = username{
self.username = "username=\(user)"
callType += 1
}
if let password : String = pass{
self.password = "password=\(password)"
callType += 1
}
if let mail : String = mail{
self.email = "email=\(mail)"
callType += 1
}
//register a new user
if(callType == 3){
paramString = "\(self.username)&\(self.password)&\(self.email)"
}
//check if user is logged, send email and password
if(callType == 2){
paramString = "\(self.email)&\(self.password)"
}
//Do call
callWithCompletionHandler { (success) in
self.flagCompletion = true
completed(success: self.flagCompletion)
}
}
callWithCompletionHandler() code:
private typealias completionAsyncCall = (success : Bool) -> Void
private func callWithCompletionHandler(completed : completionAsyncCall){
asyncJson.removeAllObjects()
//Set async call params
let request = NSMutableURLRequest(URL: NSURL(string: self.url!)!)
request.HTTPMethod = "POST"
let trimmedPostParam : String = self.paramString!.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())
request.HTTPBody = trimmedPostParam.dataUsingEncoding(NSUTF8StringEncoding)
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { data, response, error in
guard error == nil && data != nil else {
// check for fundamental networking error
print("error=\(error)")
return
}
if let httpStatus = response as? NSHTTPURLResponse where httpStatus.statusCode != 200 {
// check for http errors
print("statusCode should be 200, but is \(httpStatus.statusCode)")
print("response = \(response)")
}
let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
let result : AnyObject = responseString!.parseJSONString!
if let nsMutableResult = result as? NSMutableArray{
print("NSMutableArray")
}
if let nsDictResult = result as? NSMutableDictionary{
self.parseMutableDictionary(nsDictResult)
}
self.flag = true // true if download succeed,false otherwise
completed(success: flagAsyncCall!)
}
task.resume()
}

Answer 1

On login button press call :
apiCall.callCheckIsUserLogged(nil, password : self.passwordField.text, email: self.mailField.text){ (ok) in
if ok {
self.performSegueWithIdentifier("Identifier", sender: self)
} else {
print("User not logged in")
}
}
Because your callCheckIsUserLogged method already returns if user logged in or not.
internal typealias completion = (success : Bool) -> Void