How to check if request is ajax or not in codebehind - ASP.NET Webforms

You could create your own extension method much like the one in the MVC code

E.g.

public static bool IsAjaxRequest(this HttpRequest request)
{
    if (request == null)
    {
        throw new ArgumentNullException("request");
    }

    return (request["X-Requested-With"] == "XMLHttpRequest") || ((request.Headers != null) && (request.Headers["X-Requested-With"] == "XMLHttpRequest"));
}

HTHs,
Charles

Edit: Actually Callback requests are also ajax requests,

    public static bool IsAjaxRequest(this HttpRequest request)
    {
        if (request == null)
        {
            throw new ArgumentNullException("request");
        }
        var context = HttpContext.Current;
        var isCallbackRequest = false;// callback requests are ajax requests
        if (context != null && context.CurrentHandler != null && context.CurrentHandler is System.Web.UI.Page)
        {
            isCallbackRequest = ((System.Web.UI.Page)context.CurrentHandler).IsCallback;
        }
        return isCallbackRequest || (request["X-Requested-With"] == "XMLHttpRequest") || (request.Headers["X-Requested-With"] == "XMLHttpRequest");
    }

Try to check if the ScriptManager IsInAsyncPostBack :

ScriptManager.GetCurrent(Page).IsInAsyncPostBack

Generally, you will need to test for the X-Requested-With header, ensuring that its value is 'XMLHttpRequest'. I'm not a C# developer (yet), but a quick google search says that in C# it goes something like this:

Request.Headers["X-Requested-With"] == "XMLHttpRequest";