Re: How to force creation of COM object through method call

"Igor Tandetnik" <>
Wed, 11 Feb 2009 13:52:39 -0500
Matt Houser <> wrote:

I have 2 ATL COM objects:
1. CObject1 implements IObject1
2. CObject2 implements IObject2

I don't want consumers of the classes to be able to create a CObject1
directly. Instead, I want them to use IObject2::CreateObject1() to
create the object.

1. How do I hide a COM object from being created external to my ATL

Don't derive it from CComCoClass, don't write a coclass statement for it
in the IDL, don't list it in OBJECT_ENTRY[_AUTO]. This way it doesn't
have a CLSID associated with it.

2. When I do create my object internally, do I create a CObject1 and
return it, or do I do CoCreateInstance() and return that?

The usual pattern goes like this:

STDMETHODIMP CObject2::CreateObject1(IObject1** pp) {
    if (!pp) return E_POINTER;
    *pp = NULL;

    CComObject<CObject1>* pObj = NULL;
    HRESULT hr = CComObject<CObject1>::CreateInstance(&pObj);
    if (pObj) {

        // any initialization you may need to perform;
        // the name "Init" is for exposition only.

        hr = pObj->QueryInterface(pp);

    return hr;

With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

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