您可以创建自己的扩展方法，就像MVC代码中的方法一样

例如

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"));
}

查尔斯· HTH

编辑： 实际上，回调请求也是ajax请求，

    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");
    }