Can dataTaskWithRequest be completed before new view controller load? - swift

Question

I am new to swift and I am trying to do post request using dataTaskWithRequest. I have two view controllers, LoginViewController and SecondViewController. In the LoginViewController I have submit button to submit form login and then go to the second view. However in the button action function I called dataTaskWithRequest to get authentication.
How can dataTaskWithRequest complete his task before SecondViewController load?

Answer 1

The key here is that the login view controller's button should not be a segue to the second view controller. Instead, it should simply be an #IBAction which performs the authentication with the dataTaskWithRequest, and only if you determined it was successful in the completionHandler closure, would it programmatically transition to the next view controller.
So, let's pick that apart:
Hook up button in login scene to an #IBAction, which creates a request, initiates it, and in the completion block determines if it was successful and if so, tells the :
#IBAction func didTapLoginButton(sender: UIButton) {
let request = NSMutableURLRequest(URL: NSURL(string: "loginurl")!)
request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
request.HTTPBody = ...
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { (data, response, error) -> Void in
if data == nil {
// handle error here
println("\(error)")
} else {
// parse response here and determine if successful
var loginSuccessful: Bool = ...
if loginSuccessful {
dispatch_async(dispatch_get_main_queue()) { () -> Void in
self.performSegueWithIdentifier("SegueToSecond", sender: sender)
}
}
}
}
task.resume()
}
Clearly, there's a lot more you might want to do there (e.g. tell the user if the authorization failed, etc.), but this illustrates the moving parts:
create request;
in completionHandler, see if authorization succeeded; and
anything you do with the UI must be dispatched back to the main queue.
Note, the above assumes you have a segue from the login scene to the second scene. You can do this by control drag from the view controller icon above the login scene to the second scene:
When that's done, select the segue and give it a unique storyboard id (the same one you will use in the #IBAction code, above):