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VB Shell Programming by J.P. Hamilton

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Chapter 9. Copy Hook Handlers

Copy hook handlers are invoked every time a shell folder or printer object is moved, deleted, copied, or renamed. Their sole purpose is either to approve or to disapprove the operation in question. They take no part in the operations themselves, and they don’t care about the results. When one of the aforementioned processes is initiated, the shell provides the name of the source object, the name of the destination object, and the action being performed to the copy hook handler. The handler merely says, “Yeah, go ahead,” or “Stop right there!” That’s it. In fact, the copy hook handler is not even notified of whether the action was successful. It is merely a sentry that stands guard over a particular folder or printer.

Copy hook handlers are a little different from the other shell extensions we have discussed. First and foremost, they are not associated with file types, but rather with shell folders and printer objects. Second, they implement only one interface, ICopyHook. If you remember, the previous shell extensions were first initialized either through IShellExtInit or IPersistFile. In contrast, copy hook handlers depend on neither interface. ICopyHook contains one method, CopyCallback, that provides everything the handler will need, initialization and all. There is another major difference, but we’ll need to look at the definition for ICopyHook::CopyCallback to see it:

UINT CopyCallback(
    HWNDhwnd,
    UINT wFunc,
    UINT wFlags,
    LPCSTR pszSrcFile, DWORD ...

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