MVC action filters using parameters passed to ActionResult?

I created a custom Action Filter with no problem.

But I would like to modify the Action Filter to use some of the parameters actually passed to my method.

So if I have the following method:

[HttpPost]
[MyAttribute]
public ActionResult ViewUserDetails(Guid userId)
{
     // Do something
}

How can I get access to userId from within MyAttribute ? Is there a way I can directly pass it in?

You can try OnActionExecuting override, where you do have access to action parameters.

public class MyAttribute: ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if (filterContext.ActionParameters.ContainsKey("userId"))
        {
            var userId = filterContext.ActionParameters["userId"] as Guid;
            if (userId != null)
            {
                // Really?! Great!
            }
        }
    }
}