Hey all,
My development machine is Windows XP. I'm using Intelligencia's URLRewriter.NET httpmodule to handle URL rewriting. I'm also using ScottGu's Form Control Adapter trick to catch postbacks.
Here's the problem - Sometimes, AJAX will fail. The controls inside the UpdatePanels will work. However, they will cause the whole page to refresh instead of just the area inside the UpdatePanels. This bug happens randomly. After days of working on this problem, I have not found a way to reproduce the bug. This has been very, very frustrating.
When I attach the Visual Studio debugger to IE, the page will break on this line :
Sys.WebForms.PageRequestManager._initialize('ScriptManager1', document.getElementById('form1'));
This is the error that I get :
Microsoft JScript runtime error: 'Sys' is undefined
When I try to debug the page in Firefox using the FireBug plugin, I get the five following errors :
I'll get three errors for the following line :
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
One of those errors comes from WebResource.axd, and two of them come from ScriptResource.axd
I'll get a "Sys is not defined" error from my index.aspx, although FireBug apparently doesn't know which line is throwing the error.
Finally, I'll get a "Sys is not defined" error from this line in my index.aspx:
Sys.WebForms.PageRequestManager._initialize('ScriptManager1', document.getElementById('form1'));
I can solve the problem temporarily by disabling the UrlRewriter. There's a line in web.config that specifies when the URLRewriter should rewrite a URL. After I take this line out of the web.config, I'll reload a page on the site, and AJAX will be working fine again. I'll then put the line back in web.config, thus enabling the URLRewriter. AJAX will continue to work fine. In other words, by taking out the URLRewriter and putting it back in again, the problem will be solved until the next time it randomly happens again. Weird, huh?
If you have any insight at all into the nature of this problem, please let me know. Likewise, if you can tell me how to debug this monster, please let me know, as I am at an utter loss at this point.
I believe UrlRewriter allows you to add exclusions based on header data. If so, exclude any requests with the request header "X-MicrosoftAjax: Delta=true". That will prevent it from interfering with any partial postbacks.Thanks for the advice! This bug has driven me *insane!* I swear, I must have spent at least 2 1/2 days on this thing.
Fortunately, I think I made a breakthrough today.
URLRewriter.NET requires that you specify which URLs to intercept. Naively, I had given it the following configuration :
<rewrite url="(.*)" to="${UrlTransformer($1)}" /
Basically, I had told it to intercept all incoming URLs. I think this was a mistake.
Somebody on a forum suggested that, if you get the "Sys is undefined" error, you should try to take the URL for the ScriptResource.axd file and paste it into your address bar and see what happens. When I did that, instead of being offered the opportunity to download ScriptResource.axd, I noticed that URLRewriter had picked up on the URL and was trying to do a rewrite! This could mean that IIS never properly received the request for ScriptResource.axd, and thus the client never recieved it. This would explain the JScript error and subsequent AJAX failure.
I went ahead and entered the following new configuration for URLRewriter :
<rewrite url="^(.*\.aspx)$" to="${UrlTransformer($1)}" />
So now, it's only picking up URLs that end in .aspx. So far, everything is working exactly as it should. However, I am hesitant to close the case on this for two reasons :
1) This bug has been incredibly hairy, and there have been a few other occasions where I was *sure* I had solved the problem. Thus I am hesitant to call it prematurely.
2) The incredibly random nature of the bug. This is really what made this bug so difficult; the fact that there was no reliable way to reproduce it. Even if I am correct about the cause of the bug, why in the world would it occur so randomly? I know that the browser will cache the ScriptResource.axd code. Could the bug's occurance coincide with the browsers' cache being flushed? Was this problem really more likely to occur when the network was slow, or was I just imagining things? Why would removing the line from the web.config and then replacing it again make a difference?
I may never know the answers to these questions.
In any case, thank you for your help. Your suggestion will be the first thing that I try if my current solution doesn't work.
