Re: COM object: Store DWORD value right before interface vtable

From:

"Scot T Brennecke" <ScotB@MVPs.spamhater.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Tue, 28 Apr 2009 02:21:40 -0500

Message-ID:

<#gN26H9xJHA.5728@TK2MSFTNGP03.phx.gbl>

Would it seem a little less "hackish" to you if you considered it the 4-char (but not terminated)
ANSI string "HIML" ?

"Timo Kunze" <TKunze71216@gmx.de> wrote in message news:Of$F9r5xJHA.1380@TK2MSFTNGP05.phx.gbl...

Hi,

I've created a custom implementation of the IImageList interface. It's a
COM object and derives from CComObjectRootEx, CComCoClass, IImageList
and an internal interface called IImageListPrivate. The COM map:
BEGIN_COM_MAP(CAggregateImageList)
COM_INTERFACE_ENTRY(IImageList)
COM_INTERFACE_ENTRY_IID(IID_IImageListPrivate, IImageListPrivate)
END_COM_MAP()

However, this custom IImageList object can not yet be used like a
regular image list, because comctl32.dll looks for a magic value
(0x4C4D4948). This magic value must be stored right before the
IImageList vtable. How can I achieve this?

This code "works", but is hackish as hell:

HIMAGELIST hImageList = IImageListToHIMAGELIST(pMyImageList);
DWORD* p = reinterpret_cast<DWORD*>(hImageList) - 1;
*p = 0x4C4D4948;
SetImageList(hImageList, LVSIL_NORMAL);

How can this be done properly?
Timo
--
www.TimoSoft-Software.de - Unicode controls for VB6
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