How to modify metadata

BaseController.cs

    public class BaseController : Controller
    {
        protected override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            var keywords = filterContext.ActionDescriptor.GetCustomAttributes(typeof(MetaKeywordsAttribute), false);
            if (keywords.Length == 1)
                ViewData["MetaKeywords"] = ReplaceRouteData(((MetaDescriptionAttribute)keywords[0]).Value);

            base.OnActionExecuting(filterContext);
        }



        private string ReplaceRouteData(string value)
        {
            foreach (var kvp in ControllerContext.RouteData.Values)
            {
                value = value.Replace("{" + kvp.Key + "}", kvp.Value.ToString());
            }
            return value;
        }

    }