iOS 7 PreferredStatusBarStyle not working.

Hello!

In my iPhone application I set UIViewControllerBasedStatusBarAppearance=YES, and in ViewController have this code:

public override UIStatusBarStyle PreferredStatusBarStyle ()
        {
            return UIStatusBarStyle.LightContent;
        }

But, this code not called and status bar still black color on black background. I have found a lot of questions on SOF, but nothing work;