Re: MFC Icon Handler's IExtractIcon::GetIconLocation() never gets

From:

"Michael Phillips, Jr." <mphillips53@nospam.jun0.c0m>

Newsgroups:

microsoft.public.platformsdk.shell,microsoft.public.vc.mfc

Date:

Mon, 6 Aug 2007 11:14:10 -0400

Message-ID:

<e2roHzD2HHA.484@TK2MSFTNGP06.phx.gbl>

There appears to be a problem with your icon handler's interface
implementation.

You should see the following in your debugger:
1) The shell should load your icon handler and call your IClassFactory and
get an IExtractIcon interface.
2) It then calls QueryInteface on your IExtractIcon interface pointer to get
the IPersistFile interface.
3) If QueryInterface returns an IPersistFile interface, it then calls Load
and looks for S_OK on return.
4) If S_OK, then the shell should call your icon handler's GetIconLocation
and Extract methods.

"nomad" <nomad@discussions.microsoft.com> wrote in message
news:75A9DC70-F368-4700-9EFB-7D83E8278B4A@microsoft.com...

"Jim Barry" wrote:

nomad wrote:

Yes, the MFC declarations for everything are much cleaner

Cleaner than what?

Well, ATL, for one thing.

Anyway, debugger aside, I've got a test app now and I can verify that I
can
load the DLL and call into the IExtractIcon interface if I call
::CoInitialize(), CoCreateInstance(), do a QueryInterface(), and then call
the method off the pointer I get back:

   ::CoInitialize(NULL);

IUnknown* pUnk(NULL);

result = ::CoCreateInstance(kIHCLSID, NULL, CLSCTX_INPROC_SERVER,
IID_IUnknown,
reinterpret_cast<LPVOID*>(&pUnk));

IPersistFile* pIPF(NULL);

if (S_OK == pUnk->QueryInterface(IID_IPersistFile,
reinterpret_cast<LPVOID*>(&pIPF)))
{
ASSERT(S_OK == pIPF->Load(_T("<path to my data file>"), 0));
}

IExtractIcon* pIEI(NULL);
TCHAR path[MAX_PATH];

if (S_OK == pUnk->QueryInterface(IID_IExtractIcon,
       reinterpret_cast<LPVOID*>(&pIEI)))
{
int iIndex(0);
UINT wFlags(0);

if (S_OK == pIEI->GetIconLocation(0, path, MAX_PATH, &iIndex, &wFlags))
{
if (S_OK == pIEI->Extract(path, iIndex, &fHBigIcon, &fHSmallIcon,
  MAKELONG(32, 16)))
{
(void) fBigIcon.SetIcon(fHBigIcon);
(void) fSmallIcon.SetIcon(fHSmallIcon);
}
}
}

That all works fine. I can also do it using SHGetDesktopFolder() and the
various related calls:

   ::CoInitialize(NULL);

   if (FAILED(SHGetDesktopFolder(&deskFolder)))
       return TRUE;

   if (FAILED(deskFolder->ParseDisplayName(NULL, NULL,
   _T("g:\\development\\projects\\sample files\\files with
embedded previews\\biotite.cmdf"),
   NULL, &pidlLocal, NULL)))
   {
       deskFolder->Release();
       return TRUE;
   }

   pidlRelative = ILClone(ILFindLastID(pidlLocal));
ILRemoveLastID(pidlLocal);

   if (FAILED(deskFolder->BindToObject(pidlLocal, NULL, IID_IShellFolder,
(void**)&appObject)))
   {
       deskFolder->Release();
       ILFree(pidlLocal);
       return TRUE;
   }

ILFree(pidlLocal);

   hr = appObject->GetUIObjectOf(NULL, 1, (LPCITEMIDLIST*)&pidlRelative,
IID_IExtractIcon, NULL,
       (void**)&extractIcon);

But if I attach to an explorer window with the debugger, what happens is
that my IPersistFile::Load() method gets called, then I load the interface
for IExtractIcon, and, right after that, my IExtractIcon::Release() method
gets called (apparently from CoWaitForMultipleHandles()). So the shell
gets
the IExtractIcon interface, and releases it without (apparently) calling
anything.