XMLHttp Panel post fails with 404...app_offline trick

[Doug Swanson]

I have a telerik radgrid inside of an xmlhttp panel that I refresh at a given interval with the following javascript...
function startWorklistRefresh() {
                if (wlIntervalId == 0) {
                    wlIntervalId = setInterval("reloadWorklist();", wlCtrlAutoRefreshRate);
                }
            }
            function reloadWorklist() {
                $find("<%= XmlGridPanel.ClientID %>").set_value("Reload");
            }
function OnClientResponseError(panel,args){
    alert('wtf');
}

We update our site using the app_offline.htm trick for IIS. The problem is that I can see (via FF/Firebug) the reloadworklist happening but there are 404 errors happening (as expected) when I take the site offline...but the user is does not see our app_offline page..I tried adding a clientside event for OnClientResponseError but that event was never hit...what I would like to have is a hook so I can redirect the user to some default.aspx page...I also tried the custom errors web.config but apparently that doesn't take effect for an xmlhttppanel request...any help would be greatly appreciated.

thanks
ds

[Pero]

Hello Doug,

The XmlHttpPanel uses ASP.NET Callback mechanism to update its content. How the XmlHttpPanel will behave in such scenario (when app_offline.html is present in the root directory) will entirely depend on the ASP.NET Callback mechanism. The callback is initiated using the WebForm_DoCallback method, which takes as an argument the javascript method that will be invoked if an error occurs. Basically, if an error occurs you will be able to handle the OnClientResponseError client-side event of the XmlHttpPanel, but an error is not thrown and the event is not fired.
I tried several approaches to track whether the application is offline, in the code behind, but to no avail.
Here is what I tried:

protected void XmlPanel1_ServiceRequest(object sender, Telerik.Web.UI.RadXmlHttpPanelEventArgs e)
{
    Response.StatusCode = 404;

    if (Response.StatusCode != 200)
    {
        throw new Exception("Application Offline!");
    }
}

I will continue investigating the issue, and if anything comes up I will follow-up in this thread. If you find a solution, could you please share it with us? I am sure it will be of help to other members of the community.

Best wishes,
Pero
the Telerik team