UIKeyboardTaskQueue may only be called from the main thread

You should call your UIAlertController on the main thread because you're dealing with the ui.

Swift 2.X

dispatch_async(dispatch_get_main_queue(),{                var alert = UIAlertController(title: "Chargement", message: "Envoi des informations...", preferredStyle: UIAlertControllerStyle.Alert)                viewController.presentViewController(alert, animated: true, completion: nil)                answer = NSString(data: data!, encoding: NSUTF8StringEncoding)!                print(answer)             var complete = false    alert.dismissViewControllerAnimated(true, completion: { () -> Void in        complete = true    })    while(!complete)    {    }}

Swift 4.2

DispatchQueue.main.async {    var alert = UIAlertController(title: "Chargement", message: "Envoi des informations...", preferredStyle: UIAlertControllerStyle.Alert)    viewController.presentViewController(alert, animated: true, completion: nil)    let answer = String(data: data!, encoding: .utf8)!    print(answer)    var complete = false    alert.dismissViewControllerAnimated(true, completion: { () -> Void in        complete = true    })    while(!complete)    {    }}

For swift 3.x and 4.x

DispatchQueue.main.async(execute: {// work Needs to be done })