I'm trying to write a Windows Explorer thumbnail handler for our custom file type. I've got this working fine for the preview pane, but am having trouble getting it to work for the thumbnails.

Windows doesn't even seem to be trying to call the DllGetClassObject entry point.

Before I continue, note that I'm using Windows 7 and unmanaged C++.

I've registered the following values in the registry:

HKCR\CLSID\<my guid>
HKCR\CLSID\<my guid>\InprocServer32 (default value being path to my DLL)
HKCR\CLSID\<my guid>\InprocServer32\ThreadingModel (value = "Apartment")
HKCR\.<my ext>\shellex\{E357FCCD-A995-4576-B01F-234630154E96} (value = my guid)

I've also tried using the Win SDK sample, and that doesn't work. And also the sample project in this article (http://www.codemonkeycodes.com/2010/01/11/ithumbnailprovider-re-visited/), and that doesn't work.

I'm new to shell programming, so not really sure the best way of debugging this. I've tried attaching the debugger to explorer.exe, but that doesn't seem to work (breakpoints get disabled, and none of my OutputDebugStrings get displayed in the output window). Note that I tried setting the "DesktopProcess" in the registry as described in the WinSDK docs for debugging the shell, but I'm still only seeing one explorer.exe in the task manager - so that "may" be why I can't debug it??

Any help with this would be greatly appreciated!

Regards, Dan.