ASP.net MVC returning JSONP

Question

I am looking to return some JSON across domains and I understand that the way to do this is through JSONP rather than pure JSON.
I am using ASP.net MVC so I was thinking about just extending the JsonResult type and then extending the Controller so that it also implemented a Jsonp method.
Is this the best way to go about it or is there a built-in ActionResult that might be better?

---

Solution: I went ahead and did that. Just for reference sake I added a new result:

public class JsonpResult : System.Web.Mvc.JsonResult
{
    public override void ExecuteResult(ControllerContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException("context");
        }

        HttpResponseBase response = context.HttpContext.Response;

        if (!String.IsNullOrEmpty(ContentType))
        {
            response.ContentType = ContentType;
        }
        else
        {
            response.ContentType = "application/javascript";
        }
        if (ContentEncoding != null)
        {
            response.ContentEncoding = ContentEncoding;
        }
        if (Data != null)
        {
            // The JavaScriptSerializer type was marked as obsolete prior to .NET Framework 3.5 SP1
        #pragma warning disable 0618
            HttpRequestBase request = context.HttpContext.Request;

            JavaScriptSerializer serializer = new JavaScriptSerializer();
            response.Write(request.Params["jsoncallback"] + "(" + serializer.Serialize(Data) + ")");
        #pragma warning restore 0618
        }
    }
}

and also a couple of methods to a superclass of all my controllers:

protected internal JsonpResult Jsonp(object data)
{
    return Jsonp(data, null /* contentType */);
}

protected internal JsonpResult Jsonp(object data, string contentType)
{
    return Jsonp(data, contentType, null);
}

protected internal virtual JsonpResult Jsonp(object data, string contentType, Encoding contentEncoding)
{
    return new JsonpResult
    {
        Data = data,
        ContentType = contentType,
        ContentEncoding = contentEncoding
    };
}

Works like a charm.

Answer 1

Here is a simple solution, if you don't want to define an action filter

Client side code using jQuery:

  $.ajax("http://www.myserver.com/Home/JsonpCall", { dataType: "jsonp" }).done(function (result) {});

MVC controller action. Returns content result with JavaScript code executing callback function provided with query string. Also sets JavaScript MIME type for response.

 public ContentResult JsonpCall(string callback)
 {
      return Content(String.Format("{0}({1});",
          callback, 
          new JavaScriptSerializer().Serialize(new { a = 1 })),    
          "application/javascript");
 }