Windows Shell Extensions in .NET

• By Shawn Wildermuth
• Jan 23, 2004

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Windows Shell Programming

Like most of the developers out in the world, I have a bag of tools that I have developed over the years. In the old days, these tools usually took the form of command-line utilities to do a myriad of different tasks. As time wears on, I spend less and less of my time at a command line. I still need these tools, but it would be really useful if I could integrate them into the Windows environment.

Understanding Shell Extension Handlers

The Windows Explorer is a wonderful little tool. It may look like just a typical file/folder viewer, but it is actually a bit more simplistic than that: The Windows Explorer is just an application that exposes the Windows Shell. The view of the file system is called the Windows Shell. You will see the same behavior all around Windows; file dialogs, Internet Explorer's FTP view, and more.

Luckily for us, Microsoft has created a way to hook into the Shell to add our own functionality. There are different types of Shell Extensions that we can create. Some of the handlers are based on the type of file the user is looking at (see Table 1).

Table 1. File-based Shell Extension Types

Other extensions are based on the operation that the user is attempting to do in the Shell, as shown in Table 2.

Table 2. Operation-based Handlers

For this article, we will create a simple Shortcut Menu Handler. The handler will show up only when the user opens a folder's popup menu, as shown in Figure 1.

Figure 1 Our shell extension.

Our extension will look at a folder (and all its subfolders) and clean any temporary files. But how will it work?