访问ASP.NET MVC操作参数

这一定很简单,但我好像想不出来。我正在操作筛选器中设置操作参数,如下所示:

public class MyFilter : ActionFilterAttribute
{
    public override void OnActionExecuting (ActionExecutingContext filterContext)
    {
        filterContext.ActionParameters["MyParam"] = "MyValue";
    }
}

我将过滤器应用于整个控制器,如下所示:

 [MyFilter]
 public class HomeController : Controller
 {
      public ActionResult Index()
      {
           // How do I access MyParam here?
           return View();
      }
 }

}

如何在action方法中访问myparam?