Easy shell extensions

Posted on 12 Sep 2002 at 16:37

Shell extensions are one of the more esoteric aspects of Windows programming. You're probably aware that Windows Explorer is very versatile and can support a number of types of shell extension or plug-in. Thanks to Microsoft's excessive (and, in my opinion, unwarranted) fondness for the COM object model, shell extensions have to be written as small COM servers - DLLs that need to be registered with the system before they can be used. Once that's done, Explorer will transparently call your extensions as required.

While you're developing a shell extension, you'll frequently need to unregister the extension, which is done using this command-line:
REGSVR32 /u IconHandlerDemo.dll
Once you've unregistered an extension, you can usually delete its DLL, but you'll sometimes find Delphi will complain that it's unable to create a new DLL because Windows Explorer still has it in use. On such occasions, it's necessary to 'pull the plug' on Windows Explorer, as previously described, before you can delete the existing DLL. However, these minor irritations aside, I think you'll agree that creating a shell extension in this way is infinitely easier than using Microsoft tools.
As a side benefit, high-quality shell controls such as the Shell Control Pack from Plasmatech (www.plasmatech.com) are fully compatible with Explorer's shell-extension technology, and you'll find that a registered shell extension works perfectly with these components. You can purchase version 1.1 of Shell+ for a remarkably cheap $80 (£54), all the more remarkable because full source code is included. Version 1.2 of the component set will be out soon and this will apparently include new components for implementing shell links, drag-and-drop operations and more. Highly recommended.

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