Swift - Function doesn't wait for results - ios

Question

I've been trying to get information out of a server call. Which already works fine, but when I want to use the information to make a dialogue box appear it doesn't really work. It goes too fast to the next line. The only way I could make it work is by delaying the next bit in the code but considering it's a server call I can't determine how long it'll always take. I tried using dispatch_sync but it didn't work at all.
func logIn(username: String, password: String) -> Void {
var error: NSError?
var call = "api/usersession/"
var login = "username=" + username + "&password=" + password
API().getLogin(login, api:call, { (data) -> Void in
let json = JSON(data: data, error: &error)
println(json.self)
let status = json["status"].stringValue!
if (status == "1") {
alertController = UIAlertController(title: "Something went wrong", message: json["result"].stringValue, preferredStyle: UIAlertControllerStyle.Alert)
alertController.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil))
} else {
alertController = UIAlertController(title: "Welcome!", message: "You're signed in", preferredStyle: UIAlertControllerStyle.Alert)
}
})
}
I believe that whenever the code gets to the "getLogin" part it just immediately goes on to return whatever it has (which is always nothing). When I say that self.presentViewController needs to delay by an amount then it does work, but this would make the app feel a bit clunky.
Edit:
func getLogin(login: String, api: String, success: ((apiData: NSData!) -> Void)) {
var request = NSMutableURLRequest(URL: NSURL(string: website + api)!)
var learn = API()
var postString = login
request.HTTPMethod = "POST"
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
learn.httpRequest(request, callback:{(data, error) -> Void in
if let urlData = data {
success(apiData: urlData)
}
})
}
And httpRequest:
func httpRequest(request: NSURLRequest!, callback: (NSData?,
String?) -> Void) {
var configuration =
NSURLSessionConfiguration.defaultSessionConfiguration()
var userPassWordString = apiusername + ":" + apipassword
let userPasswordData = userPassWordString.dataUsingEncoding(NSUTF8StringEncoding)
let base64EncodedCrendtial = userPasswordData!.base64EncodedStringWithOptions(nil)
let authString = "Basic \(base64EncodedCrendtial)"
configuration.HTTPAdditionalHeaders = ["Authorization": authString]
var session = NSURLSession(configuration: configuration,
delegate: self,
delegateQueue:NSOperationQueue.mainQueue())
var task = session.dataTaskWithRequest(request){
(data: NSData!, response: NSURLResponse!, error: NSError!) -> Void in
if error != nil {
callback(nil, error.localizedDescription)
} else {
var result = NSData(data: data)
callback(result, nil)
}
}
task.resume()
}

Answer 1

It goes too fast to the next line.
You need to think about asynchronous operations. When you do something that's going to take time, whether it's making a network request to a server or asking the user to provide some information, you don't just make a function call and expect the results to show up immediately. Instead, you call a function or method that starts the process, and then you go off and do other things until the process completes. For a network request, that usually means that you provide a delegate object or a completion block that gets called when the connection has new information. When dealing with the user, you might put up a dialog box and leave it at that -- the process continues when the user triggers an action by tapping some button or filling in some field.

Answer 2

I managed to fix it by making the UIAlertController present itself from the function itself like so:
if (status == "1") {
alertController = UIAlertController(title: "Er ging iets fout", message: json["result"].stringValue, preferredStyle: UIAlertControllerStyle.Alert)
alertController.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil))
UIApplication.sharedApplication().keyWindow?.rootViewController?.presentViewController(alertController,animated: true, completion:nil)
} else {
alertController = UIAlertController(title: "Welcome!", message: "You're signed in!", preferredStyle: UIAlertControllerStyle.Alert)
alertController.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil))
UIApplication.sharedApplication().keyWindow?.rootViewController?.presentViewController(alertController,animated: true, completion:nil)
}