Open C:\windows\assembly\gac_msil from C#

Question

How can I open C:\windows\assembly\gac_msil in a Windows Explorer window using C#?

Explanation: When I deploy an assembly to the GAC in my development environment, I like deploying the .pdb symbol file to the same directory as the assembly located at C:\Windows\assembly\GAC_MSIL\AssemblyName\Version__PublicKeyToken\. That way if I want to attach the Visual Studio debugger, it automatically finds the symbol file.

I've built a little utility that detects when I add one of my assemblies to the GAC and I want it to show a button that pops open the directory for me. I have the button and the path, but starting a process that launches explorer.exe with the path doesn't work. The only way I know of to open this directory in Windows is through the Run dialog.

You can't get to it within explorer or using the command line command: explorer.exe "C:\Windows\assembly\GAC_MSIL...". Only if you type the path into the Run dialog. So how do I do what the Run dialog is doing?

Answer 1

As Hans Passant at one time had answered, the old GAC is displayed by a shell extension which masks the directory structure. This is to make sure the assemblies in the GAC are managed properly. Opening the directory structure is intentionally not supported. In .NET 4, that is no longer the case so if you can upgrade, that's the way to go.

To programmatically open the old GAC there are a few options but again, it is normally masked for a reason. Options:

1. Remove the shell extension. You can unregister Shfusion.dll, open the directory, then re-register it. This, of course, could go wrong and leave you with Shfusion.dll permanently unregistered. This would allow other users to freely mess with the GAC directory structure and files which would cause it to become invalid and fall out of sync with the registry = bad.

2. Disable the shell extension. The HKLM Fusion registry key can have a DisableCacheViewer DWORD value. When set to 1, it will disable the view. The key can be set to 1, the window opened, then the key can be set back to 0. This approach has the same risks as option 1. Additionally, as a user (Damien) whose comment seems to have been deleted pointed out, other processes may also use this global key causing a race condition = bad.

3. Use a 3rd party application like Total Commander (thanks to Csaba Toth) or Far Manager to view the directory structure instead of Explorer. The downside here is, assuming they can even accept arguments to allow them to open to the GAC directory, it would require installing that software everywhere I want to run my app.

If you are considering using options 1 or 2, be aware that in most scenarios they are a bad idea and should be avoided unless you are messing around with your own machine. This directory structure is synchronized with the registry and should not be directly edited. Use Gacutil.exe to manage the assemblies in the GAC.