Re: COM Interface intialization

From:

"Steven Edison" <EdisonCPP@newsgroups.nospam>

Newsgroups:

microsoft.public.vc.atl

Date:

Mon, 15 Jan 2007 14:58:36 -0500

Message-ID:

<#vALX#NOHHA.5064@TK2MSFTNGP04.phx.gbl>

Thanks Brian,

but I need SetSomeData() hidden from caller.
Would have to make a whole other interface with the set functions?
I just need to return them an intialized interface that they can't set the
values within it.

Here's a better example to illustrate the need:

CComPtr<IDVDPlayer> pPlayer = NULL;
if(SUCCEEDED(pSrc->GetDVDPlayer(&pPlayer)) && pPlayer)
{
     pPlayer->GetLoadedDVD(&bstrDVDName);
     pPlayer->GetMaxVolume(&maxVol);
     pPlayer->PlayDVD();
     pPlayer->Eject();
     pPlayer->Release();
}

Where pSrc can make pPlayer have everything it needs to function properly,
but
I don't want to give that ability to the caller, in the above, the caller
can't set the
MaxVolume, only pSrc can do that. Above is vaguely similar to what I'm
trying
to do.

Igor: The downcast is what made me think the deletes and AddRefs wouldn't
work right.

The only way I can think of is another exposed interface with sets in it?
Is there a better way?

Since another programming group will be interfacing to these interfaces, I
was hoping they wouldn't
be able to see, by any means, how to intialize IDVDPlayer (in the above
example), just that they
get a ready to use interface reguardless of which DVD player manufacturer is
being used, the
customer could find out what max volume is from the interface, and use the
dvd player.

It also needs to be language independent of course, so no passing of class
pointers or anything,
and the there are methods, not just data, so structures won't do.

(DVD Players are for example purposes only, not the real product)

The only OTHER way I thought of doing it, is if pSrc could be queried for an
IDVDPlayer,
then there would have to be something like an init method to make it fill
the correct
values internally.

pSrc->QueryInterface(__uuidof(IDVDPlayer)....,&pPlayer);
pPlayer->Init();
pPlayer->get_MaxVolume(&maxVol);
pPlayer->Release();

Thanks for your thoughts and ideas.

Steven

"Brian Muth" <bmuth@mvps.org> wrote in message
news:e5RPQpNOHHA.448@TK2MSFTNGP04.phx.gbl...

"Steven Edison" <EdisonCPP@newsgroups.nospam> wrote in message
news:%23XYleLNOHHA.4604@TK2MSFTNGP06.phx.gbl...

This is probably a very simple question.
And I feel like I should know this... but....
(And I hope this is okay under ATL group.)

If I have an interface implementation like this:

CItemInfo: public CComCoClass<CItemInfo, &CLSID_ItemInfo>
{
....
    STDMETHOD(get_SomeData)(LONG* pVal); //prop
    void SetSomeData(LONG nVal); //unexposed function
   //other methods and props....
...
};

All the interface properties are read (get) only.

What I'd like to do is something like this:

STDMETHODIMP CAnotherInterfaceImpl::GetItemInfo(IUnknwn** pUnk)
{
    CItemInfo* pInfo = new CItemInfo; //above impl class
    pInfo->SetSomeData(0x42); *pUnk = (IUnknown*)pInfo;
    return S_OK;
}

The usual paradigm is something like this:

STDMETHODIMP CAnotherInterfaceImpl::GetItemInfo(IUnknwn** pUnk)
{
   CComObject<CItemInfo> *pInfo;
   pInfo = CComObject<CItemInfo>::CreateInstance (&pInfo);
   pInfo->SetSomeData(0x42);
   pInfo->AddRef(); // bring reference count up to one
   *pUnk = pInfo->GetUnknown ();
   return S_OK;
}

Brian