1 流程图

image.png

注: COM库指的是 OLE32.dll

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2 COM创建函数

COM库中有三个用于创建组件的函数:

  • CoGetClassObject
  • CoCreateInstance

  • CoCreateInstanceEx

    (1) CoGetClassObject

    创建一个类厂, 并获取类厂指针作为输出参数
    如果客户希望获取类厂对象或者要调用类厂的某些成员函数，则选用CoGetClassObject函数；

    1. HRESULT CoGetClassObject(
    2.   const CLSID& clsid, 
    3.   DWORD dwClsContext,
    4.   COSERVERINFO  *pServerInfo,
    5.   const IID& iid,
    6.   (void **)ppv
    7. );

    (2) CoCreateInstance

    此函数内部调用了 CoGetClassObject 和 CreateInstance
    在其他情况下，使用CoCreateInstance函数创建对象，这是最常用的方法

    1. HRESULT CoCreateInstance(
    2.   const CLSID& clsid, 
    3.   IUnknown *pUnknownOuter,
    4.   DWORD dwClsContext,
    5.   const IID& iid,
    6.   (void **)ppv
    7. );

    实现伪码如下

    1. HRESULT CoCreateInstance(const CLSID& clsid, IUnknown  *pUnknownOuter,
    2.           DWORD dwClsContext, const IID& iid, void  *ppv)
    3. {
    4.   IClassFactory  *pCF;
    5.   HRESULT    hr;
    7.   hr = CoGetClassObject(clsid, dwClsContext, NULL, IID_IClassFactory, (void *)pCF);
    9.   if  (FAILED(hr))
    10.       return hr;
    12.   hr = pCF->CreateInstance(pUnkOuter, iid, (void *)ppv);
    13.   pCF->Release();
    15.   return hr;
    16. }

    (3) CoCreateInstanceEx

    如果客户创建远程对象或者希望一次获取对象的多个接口指针，则选用CoCreateInstanceEx函数；

    1. HRESULT CoCreateInstanceEx(
    2.   const CLSID& clsid, 
    3.   IUnknown *pUnknownOuter,
    4.   DWORD dwClsContext,
    5.   COSERVERINFO  *pServerInfo,
    6.   DWORD dwCount,
    7.   MULTI_QI *rgMultiQI
    8. );

    3 类厂的实现

    ```cpp class CDictionaryFactory : public IClassFactory { protected:

    1. ULONG           m_Ref;

    public:

    1. CDictionaryFactory (void);
    2. ~ CDictionaryFactory (void);
    4. //IUnknown members
    5. HRESULT QueryInterface(const IID& iid, void **ppv);
    6. ULONG AddRef();
    7. ULONG Release();
    9. //IClassFactory members
    10. HRESULT CreateInstance(IUnknown *, const IID& iid, void **ppv);
    11. HRESULT LockServer(BOOL);

    };

HRESULT CDictionaryFactory::CreateInstance(IUnknown pUnknownOuter, const IID& iid, void **ppv) { CDictionary pObj;
HRESULT hr; *ppv=NULL; hr=E_OUTOFMEMORY; if (pUnknownOuter != NULL) return CLASS_E_NOAGGREGATION;

  1. pObj=new CDictionary();
  2. if (pObj== NULL) 
  3.     return hr;
  5. //Obtain the first interface pointer (which does an AddRef)
  6. hr=pObj->QueryInterface(iid, ppv);
  7. if (hr != S_OK) {
  8.     g_DictionaryNumber --; 
  9.     delete pObj;
  10. }
  11.    return hr;

}

extern “C” HRESULT __stdcall DllGetClassObject(const CLSID& clsid, const IID& iid, void *ppv) { if (clsid == CLSID_Dictionary ) { CDictionaryFactory pFactory = new CDictionaryFactory;

  1.     if (pFactory == NULL)   {
  2.         return E_OUTOFMEMORY ;
  3.     }
  5.     HRESULT result = pFactory->QueryInterface(iid, ppv);
  6.     return result;
  7. } else  {
  8.     return CLASS_E_CLASSNOTAVAILABLE;
  9. }

} ```