No shell extensions with .NET 4?
Avishkar Autar · Sep 12 2012 · .NET Platform
Shell extensions (at least in Windows, I can’t speak to other platforms) are not easy to write and require some pretty ugly native code, requiring Win32 and COM code. For most applications, the .NET Framework can usually provide a nice wrapper for such code, but not for shell extensions. Prior to .NET 4, using the .NET Framework was dangerous because, as explained in this forum post, an extension would attempt to inject a version of the .NET Framework (the version the shell extension was written in) into every application affected by the extension (i.e. every application making use of the shell component extended), but only one version of the .NET Framework can be loaded in a process, potentially creating conflicts with other applications using different versions of .NET.
.NET 4 can be loaded side-by-side with other versions of the framework, so shell extensions are technically possible, and I was happy to find an article + code sample detailing how to write an extension as part of Microsoft’s All-In-One Code Framework. Unfortunately, the code sample has since disappeared and, regarding .NET 4 shell extensions, Jialiang Ge of the All-In-One Code Framework team explains:
In .NET 4, with the ability to have multiple runtimes in process with any other runtime. However, writing managed shell extensions is still not supported. Microsoft recommends against writing them.
No much of an explanation, to say the least.