IThumbnailProvider and IInitializeWithItem

Question

I am trying to develop an IThumbnailProvider for use in Windows 7. Since this particular thumbnail would also be dependant on some other files in the same directory, I need to use something other than IInitializeWithStream to a path to work with, this being IInitializeWithItem. (Alternatively, I could use IInitializeWithFile, but that is even more frowned upon apparently.)

No matter what I do, I cannot get it to work. I have Microsoft's FileTypeVerifier.exe tool which gives the green light on using IInitializeWithItem, but when explorer calls it, it only seems to try IInitializeWithStream, ever. (This was tested by temporarily implementing said interface, and Beep()ing away in its Initialize()) Did I forget to configure something?

In short: how do I get this to work?

Answer 1

Okay, I finally found out what is the matter. To quote the Building Thumbnail Providers link on the MSDN website:

There are cases where initialization with streams is not possible. In scenarios where your thumbnail provider does not implement IInitializeWithStream, it must opt out of running in the isolated process where the system indexer places it by default when there is a change to the stream. To opt out of the process isolation feature, set the following registry value.

• HKEY_CLASSES_ROOT

  • CLSID

  • {66742402-F9B9-11D1-A202-0000F81FEDEE}

    DisableProcessIsolation = 1

I knew I was running out of process since I read elsewhere that thumbnailproviders ALWAYS ran out of process. But since that particular snippet is on almost -all- shell extension handlers, I interpreted it to be a overly happy copy-paste job, since it was -required- to run in-process the way I understood it.

And I was wrong. I hope this will help someone else in the near future. :)