animateWithDuration call after a long time when it is written in URLSession

In Swift 2.0, I am using a web API to upload and download some data. Before calling the API, I have started an activity indicator animation and want to stop it when the response of the API has come.

However, when I want to stop the animation after the API response, the indicator stops after a long time of wait.

Here is my code:

    let activityIndi = UIActivityIndicatorView(activityIndicatorStyle: .White) 
    activityIndi.startAnimating()
    flagBtn.addSubview(activityIndi)
    let urlString = NSURL(string: "URL")
    NSURLSession.sharedSession().dataTaskWithURL(urlString!, completionHandler: { (data: NSData?, _, _) -> Void in
        if data != nil {
            do {
                let jsonInfoDic = try NSJSONSerialization.JSONObjectWithData(data!, options: .AllowFragments) as! [String:AnyObject]
                if(jsonInfoDic["status"] as! Bool)
                {
                    UIView.animateWithDuration(1.0, animations: {
                        activityIndi.stopAnimating()
                        }, completion:{ (finished: Bool) -> Void in
                    })
                }
            }
            catch {  print("Exception in parsing JSON.\n\nReason: \(error)")  }
        }
    }).resume()

You need to perform UI-modifying operations on the main thread. Since the callback of dataTaskWithURL:completionHandler: is performed on a background thread (NSURLSession thread), you must dispatch the UI code as follows:

dispatch_async(dispatch_get_main_queue()) {
    activityIndi.stopAnimating()
}

Furthermore, I suspect you won't need UIView.animateWithDuration:completion: because stopAnimating performs an animation by itself.