Asp.Net MVC2 RenderAction changes page mime type?

Question

It appears that calling Html.RenderAction in Asp.Net MVC2 apps can alter the mime type of the page if the child action's type is different than the parent action's.

The code below (testing in MVC2 RTM), which seems sensible to me, will return a result of type application/json when calling Home/Index. Instead of dispylaying the page, the browser will barf and ask you if you want to download it.

My question: Am I missing something? Is this a bug? If so, what's the best workaround?

controller:

public class HomeController : Controller
{
    public ActionResult Index()
    {
        ViewData[ "Message" ] = "Welcome to ASP.NET MVC!";

        return View();
    }

    [ChildActionOnly]
    public JsonResult States()
    {
        string[] states = new[] { "AK", "AL", "AR", "AZ", };

        return Json(states, JsonRequestBehavior.AllowGet);
    }
}

view:

<h2><%= Html.Encode(ViewData["Message"]) %></h2>
<p>
    To learn more about ASP.NET MVC visit <a href="http://asp.net/mvc" title="ASP.NET MVC Website">http://asp.net/mvc&lt;/a&gt;.
</p>
<script>
  var states = <% Html.RenderAction("States"); %>;
</script>

Answer 1

It's not a bug. The JsonResult type is supposed to set the result to JSON, because that's usually what you want.

You don't really want a JSON result here, you want a JSON string. So why not just write that?

[NonAction]
public string States()
{
    string[] states = new[] { "AK", "AL", "AR", "AZ", };

    return new JavaScriptSerializer().Serialize(states);
}

Answer 2

This can be solved by explicitly forcing the mime type "back" to text/html:

return Json(states, "text/html", JsonRequestBehavior.AllowGet);

It doesn't seem like this should be necessary, though.

Answer 3

Like Craig Stuntz said the content type is supposed to change.

A better approach would be calling that action with AJAX and then assigning the returned object to the states variable in the JavaScript code.