Custom Renderer for Content Page for Windows Phone

Hello,
I want to build a custom renderer for the Content Page for windows phone.

I used this:-

`
[assembly: ExportRenderer(typeof(ContentPage), typeof(CustomPageRenderer))]
namespace Project.Phone.Helpers
{
public class CustomPageRenderer : PageRenderer
{

    protected override void OnElementChanged(ElementChangedEventArgs<Page> e)
    {
        base.OnElementChanged(e);

        var control = this.Control;
        var style = this.Style;
    }


}

}
`
but The control and the style are always null

Regards,
Mostafa