第七步 实现IClassFactory的方法

实现类CAddFactory的方法。创建一个新文件（AddObjFactory.cpp）。提供类IUnknown和IClassFactory的方法实现。AddRef,Release和QueryInterface方法实现和前面类CAddObj中这三个函数实现基本一样。在方法CreateInstance中，类CaddObj被实例化并且传回其接口指针。LockServer方法没有给出细节的实现。

HRESULT __stdcall CAddFactory::CreateInstance(IUnknown* pUnknownOuter,

                                           const IID& iid,

                                           void** ppv)

    {

    //

    //This method lets the client manufacture components en masse

    //The class factory provides a mechanism to control the way

    //the component is created. Within the class factory the

    //author of the component may decide to selectivey enable

    //or disable creation as per license agreements

    //

    //

    // Cannot aggregate.

    if (pUnknownOuter != NULL)

        {

        return CLASS_E_NOAGGREGATION ;

        }

    //

    // Create an instance of the component.

    //

    CAddObj* pObject = new CAddObj ;

    if (pObject == NULL)

        {

        return E_OUTOFMEMORY ;

        }

    //

    // Get the requested interface.

    //

    return pObject->QueryInterface(iid, ppv) ;

    }

HRESULT __stdcall CAddFactory::LockServer(BOOL bLock)

    {

    return E_NOTIMPL;

    }

/////////////////////////////////////////////////////////////////

第八步 实现DllGetClassObject的方法

一个进程内COM对象只是一个简单的WIN32DLL，他遵循既定的协议。每一个COM DLL必须有一个通过名字DllGetClassObject的出口函数。客户端将调用这个函数以得到类厂的接口（IUnknown or IClassFactory），之后就是调用CreateInstance方法。创建一个新文件（Exports.cpp），在其中实现DllGetClassObject。（代码如下）

STDAPI DllGetClassObject(const CLSID& clsid,

                         const IID& iid,

                         void** ppv)

    {

    //

    //Check if the requested COM object is implemented in this DLL

    //There can be more than 1 COM object implemented in a DLL

    //

    if (clsid == CLSID_AddObject)

        {

        //

        //iid specifies the requested interface for the factory object

        //The client can request for IUnknown, IClassFactory,

        //IClassFactory2

        //

        CAddFactory *pAddFact = new CAddFactory;

        if (pAddFact == NULL)

            return E_OUTOFMEMORY;

        else

            {

            return pAddFact->QueryInterface(iid , ppv);

            }

        }

    //

    //if control reaches here then that implies that the object

    //specified by the user is not implemented in this DLL

    //

    return CLASS_E_CLASSNOTAVAILABLE;

    }

///////////////////////////////

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