?????????在COM中對(duì)象要通過(guò)class factory的接口（通常是IClassFactory）來(lái)創(chuàng)建。在ATL中，class factory也是從CComObjectRootEx派生的COM類，它跟普通的COM類一樣，也通過(guò)CComObject或其同伴類將邏輯功能跟生存期管理分離。
?????????在ATL中，class factory類和普通類對(duì)象的創(chuàng)建都可以通過(guò)被稱為“創(chuàng)建者”的模板類來(lái)創(chuàng)建。
?????????
template?<class?T1>
class?CComCreator
{
public:
????static?HRESULT?WINAPI?CreateInstance(void*?pv,?REFIID?riid,?LPVOID*?ppv)
????{
????????HRESULT?hRes?=?E_OUTOFMEMORY;
????????T1*?p?=?NULL;
????????p?=?new?T1(pv);
????????if?(p?!=?NULL)
????????{
????????????p->SetVoid(pv);
????????????p->InternalFinalConstructAddRef();
????????????hRes?=?p->FinalConstruct();
????????????p->InternalFinalConstructRelease();
????????????if?(hRes?==?S_OK)
????????????????hRes?=?p->QueryInterface(riid,?ppv);
????????????if?(hRes?!=?S_OK)
????????????????delete?p;
????????}
????????return?hRes;
????}
};
?????????“創(chuàng)建者”通過(guò)提供一個(gè)靜態(tài)函數(shù)CreateInstance來(lái)創(chuàng)建指定類的實(shí)例，并且查詢指定的接口。第一個(gè)參數(shù)在實(shí)例化普通對(duì)象和class factory對(duì)象時(shí)會(huì)有不同：對(duì)于普通對(duì)象，通常會(huì)傳遞聚合外部對(duì)象的IUnknown指針，如果是非聚合創(chuàng)建，可以傳遞NULL（詳見(jiàn)ATL對(duì)COM實(shí)體身份的支持四）；稍后會(huì)介紹在class factory創(chuàng)建時(shí)第一個(gè)參數(shù)的用處。
?????????在ATL中，一個(gè)class factory對(duì)象只能創(chuàng)建一種類型的COM類實(shí)例。在class factory的CreateInstance函數(shù)中，它不是硬編碼被創(chuàng)建的對(duì)象類型，而是通過(guò)一個(gè)
函數(shù)指針成員變量來(lái)創(chuàng)建它所管理的對(duì)象，而這個(gè)函數(shù)指針指向的通常就是某個(gè)COM類的“創(chuàng)建者”類的CreateInstance靜態(tài)函數(shù)的地址，此地址是在class factory對(duì)象被它自身的“創(chuàng)建者”的CreateInstance函數(shù)創(chuàng)建時(shí)通過(guò)第一個(gè)參數(shù)傳進(jìn)來(lái)的，class factory重新定義了SetVoid函數(shù)，并且保存這個(gè)地址：
?????????
class?CComClassFactory?:
????public?IClassFactory,
????public?CComObjectRootEx<CComGlobalsThreadModel>
{
public:
????//?IClassFactory
????STDMETHOD(CreateInstance)(LPUNKNOWN?pUnkOuter,?REFIID?riid,?void**?ppvObj)
????{
????????HRESULT?hRes?=?E_POINTER;
????????if?(ppvObj?!=?NULL)
????????{
????????????*ppvObj?=?NULL;
????????????if?((pUnkOuter?!=?NULL)?&&?!InlineIsEqualUnknown(riid))
????????????{
????????????????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;
????}
?
????void?SetVoid(void*?pv)
????{
????????m_pfnCreateInstance?=?(_ATL_CREATORFUNC*)pv;
????}
????_ATL_CREATORFUNC*?m_pfnCreateInstance;
};
?????????根據(jù)上面的討論，一個(gè)COM類的創(chuàng)建者會(huì)像這個(gè)樣子：
?????????CComCreator<?CComObject<CMyClass> >
?????????而一個(gè)class factory的創(chuàng)建者會(huì)像這個(gè)樣子：
?????????CComCreator< CComCachedObject<CComClassFactory> >。
?????????
?????????ATL在客戶請(qǐng)求創(chuàng)建CMyClass對(duì)象時(shí)執(zhí)行的偽代碼如下：
?????????
typedef?CComCreator<?CComCachedObject<CComClassFactory>?>?CClassFactoryCreator;
typedef?CComCreator<?CComObject<CMyClass>?>?CMyClassCreator;
IClassFactory*?pcf=NULL;
CClassFactoryCreator::CreateInstance(&CMyClassCreator::CreateInstance,__uuidof(IClassFactory),&pcf);
pcf->CreateInstance(pOuter,__uuidof(IMyInterface),ppvObj);
posted on 2007-04-10 17:36
michael 閱讀(1556)
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