Swift: Return JSON string from NSURLSession task - json

Question

I'd like to get token as String type, however the following code returns error as " "String" is not convertible to "Void" ".
Could you tell me what is the problem?
In order to parse JSON, I used SwiftyJSON
func authentication() -> String {
let request = NSMutableURLRequest(URL: NSURL(string: "https://~~~/v2/authenticate/api")!)
request.HTTPMethod = "POST"
var loginID = "my_ID"
var apiKey = "my_APIKEY"
var postString:NSString = "login_id=\(loginID)&api_key=\(apiKey)"
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
data, response, error in
if error != nil {
println("error=\(error)")
return
}
println("response = \(response)")
let responseString = NSString(data: data, encoding: NSUTF8StringEncoding)
println("responseString = \(responseString)")
let json = JSON(data:data)
if let token = json["auth_token"].stringValue{
println("\(token)")
return token ///Error Here
}
}
task.resume()
}
※Edited Jan6th 7:50(GMP+9hr)
I edited as following, however I got error as ""Use of unresolved identifier "tokenString".
Please tell me how to solve the problem.
func authentication() -> String {
let request = NSMutableURLRequest(URL: NSURL(string: "https://~~~/v2/authenticate/api")!)
request.HTTPMethod = "POST"
var loginID = "my_ID"
var apiKey = "my_APIKEY"
var postString:NSString = "login_id=\(loginID)&api_key=\(apiKey)"
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
data, response, error in
if error != nil {
println("error=\(error)")
return
}
println("response = \(response)")
let responseString = NSString(data: data, encoding: NSUTF8StringEncoding)
println("responseString = \(responseString)")
let json = JSON(data:data)
if let token = json["auth_token"].stringValue{
println("\(token)")
tokenString = self.didReceiveAuthToken(token)///Edited
}
}
task.resume()
return tokenString
}
func didReceiveAuthToken(token : String) ->String{
return token
}

Answer 1

The dataTaskWithRequest closure takes a return type of void. Your method that returns a string ends immediately after task.resume() is executed and does not return anything.
Your basic problem is that you're applying synchronous thinking to an asynchronous task. One easy suggestion is to have authentication() return void (ie, nothing), and then make a separate method like didReceiveAuthToken(token : String) that is called by your completion handler when the token is received.