Question

What I want to do is force Windows to use my program as a base for creating thumbnail from some kind of files that are not images.

In Windows you can see thumbnails from images, word documents, pdf´s etc – this is what I want with other file types. I can create bitmaps from these files (which later I want to use as a thumbnails) and store them somewhere.

My question is how to connect extension with request of creating/checking if they exists thumbnail with my program and returning image/path to image. Any help and example will be very helpful.

Answer 1

You need to create a COM DLL library, with a class that implements IExtractImage.

You then register your shell extension with the file extension you support under:

HKEY_CLASSES_ROOT\[.ext]\shellex\[SID_IExtractImage]
@default = [MyExtractImageShellExtensionCLSID]

Where

• .ext is the extension of file you are creating a viewer for (e.g. .psd)
• SID_IExtractImage is the constant {BB2E617C-0920-11d1-9A0B-00C04FC2D6C1}
• MyExtractImageShellExtensionCLSID is the class id (clsid) of your shell extension that implements IExtractImage

So, if i were registering a Photoshop psd extension handler, and my COM object’s clsid is {CCB7DB3B-D073-4606-B246-2A5174D274C8}:

HKEY_CLASSES_ROOT\.psd\shellex\{BB2E617C-0920-11d1-9A0B-00C04FC2D6C1}
@default = {CCB7DB3B-D073-4606-B246-2A5174D274C8}

Then it’s just a matter of creating a COM object that implements:

• IPersist
• IPersistFile
• IPersistStream (optional)
• IExtractImage

And Explorer will use your extension to create a thumbnail of a photoshop image.

Note: If you’re running 64-bit Windows you will need a 64-bit compiler, to create a 64-bit COM object DLL, that 64-bit Windows Explorer can load.