I fiddled around with the ScriptManager suggestions - which I reckon I would have eventually got working but it seems to me that the Timer idea is easier to implement and not really(!) that much of a hack?!
Here's how I got my panel updated after the initial page render was complete...
default.aspx (BTW markdown replaces the underscore character with _)
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="AJAXPostLoadCall._Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<h2>And now for a magic trick...</h2>
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="True">
</asp:ScriptManager>
<div>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Timer ID="Timer1" runat="server" Interval="2000" ontick="Timer1_Tick" />
<asp:Label ID="Label1" runat="server">Something magic is about to happen...</asp:Label>
</ContentTemplate>
</asp:UpdatePanel>
</div>
</form>
</body>
</html>
and the code behind default.aspx.cs reads (again note the underscore _ is replaced with _ in markdown for some reason (how do I turn that off??))
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
namespace AJAXPostLoadCall
{
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
public void DoMagic()
{
Label1.Text = "Abracadabra";
}
protected void Timer1_Tick(object sender, EventArgs e)
{
// Do the magic, then disable the timer
DoMagic();
Timer1.Enabled = false;
}
}
}
So, the page loads up and the Timer (contained within the UpdatePanel) fires 2 secs after the page has loaded up (I think - I'm not sure when the Timer actually starts?). The label text is rewritten and then the Timer is disabled to stop any more updates.
Simple enough - but can you purists out there tell me if this is a Horrible Hack?