Debugging Browser Objects (Toolbars) in Internet Explorer 8 (IE8)

Wednesday, 3 June 2009 20:41 by RanjanBanerji

I have built several toolbars for IE and every now and then I end up modifying them and then end up having to debug them.  Up until now this was an easy process.  I would open the source code for the the toolbar DLL in Visual Studio (2005 or 2008) and on the debug property page I would set it to launch IE.  Any breakpoint in my code would get triggered.

Recently I upgraded to IE8.  At the same time I found a bug in one of my toolbars.  SO I set out to debug it and the moment I hit F5 I got the following error: “Error while trying to run project: Unable to start debugging.”.  So I started looking into what went wrong.  If I switched the debug setting from running IE to opening a URL in a browser then IE would launch but my toolbar DLL breakpoints were still not be called.  Was this a new IE8 security feature?  I didn’t think so as I could still debug websites by asking it to open a URL in the browser.

So then I attempted the next best way to debug.  Simply attach to the iexplore process via Visual Studio.  Uh oh! there were several iexplore processes running even though I had just one IE open.  Now I remembered reading about IE8 and how it launches each tab in its own process.  So which one do I attach to?  I went ahead and attached to all.  Still unable to debug.  This was no good.  So I started reading up on IE8 and stumbled upon this blog post: 

In the blog post under item #4 it talks about the fact that the IE8 process model is configurable.  You can what the maximum number of processes is for IE.  This is done by the following registry entry TabProcGrowth (DWORD) that is at:  HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main

If it does not exist then IE does whatever it wants to.  If set to 0 then IE will use just one process.  Now the debugger works.  I do not know if there is a better option, because with this option, post debugging its a good idea to go to the registry and remove TabProcGrowth so that IE8 can function as it was designed to.


Categories:   IE
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