OBJECT_ENTRY 映射

对象映射图:

 BEGIN_OBJECT_MAP(ObjectMap)
OBJECT_ENTRY(CLSID_Math, CMath)
END_OBJECT_MAP()

其中OBJECT_ENTRY映射为--->

#define OBJECT_ENTRY(clsid, class) {
&clsid, class::UpdateRegistry, 
class::_ClassFactoryCreatorClass::CreateInstance,  －－－－组件类厂创建
class::_CreatorClass::CreateInstance,   －－－－组件实例创建
NULL, 
0, 
class::GetObjectDescription, 
class::GetCategoryMap, 
class::ObjectMain 
},

其中的_ClassFactoryCreatorClass和_CreatorClass定义如下(都为创建类－－CComCreator)：
#define DECLARE_CLASSFACTORY() DECLARE_CLASSFACTORY_EX(ATL::CComClassFactory)
#define DECLARE_CLASSFACTORY_EX(cf) typedef ATL::CComCreator< ATL::CComObjectCached< cf > >_ClassFactoryCreatorClass;

#define DECLARE_AGGREGATABLE(x) public:/
 typedef ATL::CComCreator2< ATL::CComCreator< ATL::CComObject< x > >, ATL::CComCreator< ATL::CComAggObject< x > > > _CreatorClass;

CComCreator：

template <class T1>
class CComCreator
{
public:
    static HRESULT WINAPI CreateInstance(void* pv, REFIID riid, LPVOID* ppv)
    {
        ATLASSERT(ppv != NULL);
        if (ppv == NULL)
            return E_POINTER;
        *ppv = NULL;

        HRESULT hRes = E_OUTOFMEMORY;
        T1* p = NULL;
#pragma warning(push)
#pragma warning(disable: 6014)
        /* prefast noise VSW 489981 */
        ATLTRY(p = new T1(pv))
#pragma warning(pop)
        if (p != NULL)
        {
            p->SetVoid(pv);
            p->InternalFinalConstructAddRef();
            hRes = p->_AtlInitialConstruct();
            if (SUCCEEDED(hRes))
                hRes = p->FinalConstruct();
            if (SUCCEEDED(hRes))
                hRes = p->_AtlFinalConstruct();
            p->InternalFinalConstructRelease();
            if (hRes == S_OK)
                hRes = p->QueryInterface(riid, ppv);
            if (hRes != S_OK)
                delete p;
        }
        return hRes;
    }
};

当一个客户程序调用CoCreateInstanses时，COM将调哟DllGetClassObject。COM对DllGetClassObject
的调用最终会导致对AtlModuleGetClassObject的调用，而AtlModuleGetClassObject函数将在对象
映射图里搜索CLSID_Math条目。当函数找到它之后，AtlModuleGetClassObject将调用
&CMath::_ClassFactoryCreatorClass::CreateInstance并把&CMath::_CreatorClass::CreateInstance
作为参数传递进去。该参数被CComClassFactory里的m_pfmCreateInstance成员捕获。

CComClassFactory ：

class CComClassFactory :
    public IClassFactory,
    public CComObjectRootEx<CComGlobalsThreadModel>
{
public:
    BEGIN_COM_MAP(CComClassFactory)
        COM_INTERFACE_ENTRY(IClassFactory)
    END_COM_MAP()

    // This will be made virtual again for Beta 2
    /*virtual*/ ~CComClassFactory()
    {
    }
    
    // IClassFactory
    STDMETHOD(CreateInstance)(LPUNKNOWN pUnkOuter, REFIID riid, void** ppvObj)
    {
        ATLASSUME(m_pfnCreateInstance != NULL);
        HRESULT hRes = E_POINTER;
        if (ppvObj != NULL)
        {
            *ppvObj = NULL;
            // can't ask for anything other than IUnknown when aggregating

            if ((pUnkOuter != NULL) && !InlineIsEqualUnknown(riid))
            {
                ATLTRACE(atlTraceCOM, 0, _T("CComClassFactory: asked for non IUnknown interface while creating an aggregated object"));
                hRes = CLASS_E_NOAGGREGATION;
            }
            else
                hRes = m_pfnCreateInstance(pUnkOuter, riid, ppvObj);
        }
        return hRes;
    }

    STDMETHOD(LockServer)(BOOL fLock)
    {
        if (fLock)
            _pAtlModule->Lock();
        else
            _pAtlModule->Unlock();
        return S_OK;
    }
    // helper
    void SetVoid(void* pv)
    {
        m_pfnCreateInstance = (_ATL_CREATORFUNC*)pv;
    }
    _ATL_CREATORFUNC* m_pfnCreateInstance;
};

COM(通过CoCreateInstance)或客户程序(CoGetClassObject/CreateInstance)使用
CComClassFactory::CreateInstance来创建组件的实例。该函数实际调用m_pfmCreateInstance并把
pUnkOuter作为参数传递回去。如果pUnkOuter为空，表明客户程序没有进行集合，并且
CComCreator<CComObject<CMath>>::CreateInstance方法被使用。如果pUnkOuter不为空，那么
则表明生成了一个集合，并且使用了CComCreator<CComAggObject<CMath>>::CreateInstance方法。

CComCreator2:

template <class T1, class T2>
class CComCreator2
{
public:
    static HRESULT WINAPI CreateInstance(void* pv, REFIID riid, LPVOID* ppv)
    {
        ATLASSERT(ppv != NULL);

        return (pv == NULL) ? 
            T1::CreateInstance(NULL, riid, ppv) : 
            T2::CreateInstance(pv, riid, ppv);
    }
};