I have an ASP.net C# 4.0 website project. I am calling an ASHX handler using a jQuery AJAX postback. Normally when I debug C#, I use this method Debug > Attach to Process > select w3wp.exe and start debugging.
When I do this with my ASHX handler Visual Studio says "The breakpoint will not be hit. No symbols have been loaded for this document." Sure enough, when I run the AJAX call to the handler, the breakpoint is not hit.
What confuses me is that I can debug C# files otherwise, i.e. the code-behind of an ASPX file.
It turns out that Visual Studio will not actually load symbols for debugging until it actually tries to run the ASHX handler. My problem turned out to be elsewhere - a bug in the jQuery code that called the handler.
I didn't see this bug at first so assumed the handler was being hit. Once the handler is called, VS will then allow you to debug it. I didn't realise that ASHX handlers behaved this way, I thought they would work just like a regular C# file.