问加载指示灯不能正常工作

EN

@IBAction func addWishList(sender: AnyObject) {
     self.loading.startAnimating()
        addMovie(showMovie!) // Database add method.
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), { () -> Void in
        let controller : WishListViewController = segue.destinationViewController as! WishListViewController

        if segue.identifier == "segue" {
            controller.user = self.tmpUser //  data from Facebook to pass another controller
            dispatch_async(dispatch_get_main_queue(), { () -> Void in
                self.loading.stopAnimating()
            })
        }
    })
}