COM组件接口继承的实现

1.创建Calculate组件,添加IFun接口(注意:本例我们在Attributes中我们选择Apartment,Custom,Yes).在IFun接口中添加函数Add实现两数相加的功能(参数为[in] long n1, [in] long n2, [out, retval] long *pVal).代码如下:

STDMETHODIMP CCalCulate::Add(long n1, long n2, long *pVal)

{

   // TODO: Add your implementation code here

   *pVal = n1 + n2;

   return S_OK;

}

2.添加IFun2接口,继承IFun接口.步骤如下:

  (1)修改.idl文件:

在 interface IFun : IUnknown

     {

      [helpstring("method Add")] HRESULT Add([in] long n1, [in] long n2, [out, retval] long *pVal);

      };

下添加代码:

      [

        object,

        uuid(B9D75722-1950-405b-8BB6-9788A6DB1DB2), //是接口IFun2的标志数,可由VS的GUIDGEN.exe产生

        helpstring("IFun2 Interface"),

        pointer_default(unique)

      ]

      interface IFun2 : IFun

      {

      };

      同时将末尾    coclass CalCulate函数改为

coclass CalCulate

      {

         interface IFun;

        [default] interface IFun2;

      };

(2) 修改CalCulate.h文件

    将class ATL_NO_VTABLE CCalCulate :

public CComObjectRootEx<CComSingleThreadModel>,

                               public CComCoClass<CCalCulate, &CLSID_CalCulate>,

                               public IFun

     改为class ATL_NO_VTABLE CCalCulate :

public CComObjectRootEx<CComSingleThreadModel>,

                               public CComCoClass<CCalCulate, &CLSID_CalCulate>,

                               public IFun2

     在BEGIN_COM_MAP(CCalCulate)

              COM_INTERFACE_ENTRY(IFun)

END_COM_MAP()

中添加COM_INTERFACE_ENTRY(IFun2)

(3) 在IFun2接口中添加Sub函数,方法同添加Add函数不再重复,只是实现时改为

*pVal = n1 - n2 返回两数差.

(4) 编写客户端代码,调用IFun2接口的Add和Sub函数.