Writing a Managed Internet Explorer Extension: Part 4–Debugging

Picking up where we left of with Writing a Managed Internet Explorer Extension, debugging is where I wanted to go next. I promise I’ll get to more “feature” level stuff, but when stuff goes wrong, and it will, you need to know how to use your toolset. .NET Developers typically write some code and press F5 to see it work. When an exception, the debugger, already attached, steps up to the plate and tells you everything that is wrong. When you write an Internet Explorer Extension it isn’t as simple as that. You need to attach the debugger to an existing process, and even then it won’t treat you like you’re use to. Notably, breakpoints aren’t going to launch the debugger until the debugger is already attached. So we have a few options, and some tricks up our sleeves, to get the debugger to aide us.

Explicit “Breakpoints”
The simplest way to emulate a breakpoint is to put the following code in there:

System.Diagnostics.Debugger.Break()

Think of that as a breakpoint that is baked into your code. One thing to note if you’ve never used it before is that the Break method has a [Conditional(“DEBUG”)] attribute on it – so it’ll only work if you are compiling in Debug. When this code gets hit, a fault will occur. It will ask you if you want to close, or attach a debugger. Now is your opportunity to say “I want a debugger!” and attach.
It’ll look like just a normal Internet Explorer crash, but if you probe at the details, “Problem Signature 09” will tell you if it’s a break. When working on a BHO, check this every time IE “crashes” – it’s very easy to forget that these are in there. It’s also important that you compile in Release mode when releasing to ensure none of these sneak out into the wild. The user isn’t going to look at the details and say, “Oh it’s just a breakpoint. I’ll attach and hit ‘continue’ and everything will be OK”. Once that’s done, choose Visual Studio as your debugger of choice (more on that later) and you should feel close to home.

Read more: vcsjones

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