ASP.Net Webforms w/ AJAX Slow Rendering

Question

I have a Webforms, AJAX-enabled web page which, when rendering large amounts of data, is extremely slow to load in IE (we're married to IE - no other browser options). In an attempt to determine the source of the slowness, I viewed the HTML source (about 2.5 MB) and copied all of it (except for the Ajax JavaScript calls) to a blank .html file. IE renders this file MUCH faster than when the rendering happens through .Net. This seems to indicate that the AJAX JavaScript is slowing down the display of the page. Does this sound plausible? Any recommendations on improving performance here?

I've already eliminated as many UpdatePanel controls as I can from the page, but it doesn't seem to help with render time.

Thanks for the help!

Update... In the HTML source, I noticed that at the bottom of the screen, a call to WebForm_InitCallback() appears. When I executed this call directly through javascript:alert(WebForm_InitCallback());, the CPU spikes for 12 seconds before it completes! This call is here because I implemented ICallbackEventHandler to try to accomplish some traditional-style AJAX handling. Looking at WebResource.axd, that WebForm_InitCallback() method iterates through the entire form and attaches some kind of events to EVERY SINGLE textbox, checkbox, radiobutton, etc. So I guess I really need to abandon ScriptManager and UpdatePanel altogether here. Poop.

Andy

Answer 1

I hate to say this, but can you take the Microsoft AJAX out of the equation? Try it with doing an XMLHTTP request and populate the data yourself. That way at least you could step through the js and figure out if it is time on the server, time turning the resulting XML or JSON into an object, or time spent populating your data on screen.