title: ActionExecutingContext - ActionParameters vs RouteData
body: <p>Given the following code:</p>
  
  <pre><code>public class MyActionFilter : ActionFilterAttribute
  {
      public override void OnActionExecuting(ActionExecutingContext filterContext)
      {
          var a = filterContext.ActionParameters["someKey"];
          var b = filterContext.RouteData.Values["someKey"];          
          base.OnActionExecuting(filterContext);
      }
  }
  </code></pre>
  
  <p>What is the difference between <code>a</code> and <code>b</code> ?</p>
  
  <p>When should we be using action parameters over route data? What is the difference?</p>