How to know if the request is ajax in asp.net in Application_Error()

Question

How to know if the request is ajax in asp.net in Application_Error()

I want to handle app error in Application_Error().If the request is ajax and some exception is thrown,then write the error in log file and return a json data that contains error tips for client . Else if the request is synchronism and some exception is thrown ,write the error in log file and then redirect to a error page.

but now i cant judge which kind the request is . I want to get "X-Requested-With" from header ,unfortunately keys of headers don't contain "X-Requested-With" key ,why?

Answer 1

Testing for the request header should work. For example:

public class HomeController : Controller
{
    public ActionResult Index()
    {
        return View();
    }

    public ActionResult AjaxTest()
    {
        throw new Exception();
    }
}

and in Application_Error:

protected void Application_Error()
{
    bool isAjaxCall = string.Equals("XMLHttpRequest", Context.Request.Headers["x-requested-with"], StringComparison.OrdinalIgnoreCase);
    Context.ClearError();
    if (isAjaxCall)
    {
        Context.Response.ContentType = "application/json";
        Context.Response.StatusCode = 200;
        Context.Response.Write(
            new JavaScriptSerializer().Serialize(
                new { error = "some nasty error occured" }
            )
        );
    }

}

and then send some Ajax request:

<script type="text/javascript">
    $.get('@Url.Action("AjaxTest", "Home")', function (result) {
        if (result.error) {
            alert(result.error);
        }
    });
</script>