COM组件接口的实质及ArcGIS Object Model Diagram的理解

class IUnknown{public:virtual int QueryInterface(char*IName,void**ppv)=0;//查询接口virtual void Release()=0;                          //释放接口};

class IA:public IUnknown{public:virtual void f1()=0;virtual void f2()=0;};

class IB:public IUnknown{public:virtual void g1()=0;virtual void g2()=0;};

class A:public IA,IB{private:char*s1,*s2,*s3,*s4;public:A(){s1="This is f1()";s2="This is f2()";s3="This is g1()";s4="This is g2()";}virtual void f1(){cout<<s1<<endl;}virtual void f2(){cout<<s2<<endl;}virtual void g1(){cout<<s3<<endl;}virtual void g2(){cout<<s4<<endl;}virtual int QueryInterface(char*IName,void**ppv){if(IName=="IA"){*ppv = (IA*)(this);return 1;}else if(IName=="IB"){*ppv = (IB*)(this);return 1;}else return 0;}virtual void Release(){delete this;}};A*GreateInst(){return new A;}void CoGetInst(char*IName,void**ppv){A*a=GreateInst();a->QueryInterface(IName,ppv);}void main(){IA*pIA;CoGetInst("IA",(void**)&pIA);pIA->f1();IB*pIB;pIA->QueryInterface("IB",(void**)&pIB);pIB->g2();pIA->Release();}

一个很好的实例是关于ArcGIS二次开发的实例：

            IMap pMap = axMapControl1.Map;            IActiveView pActiveView = pMap as IActiveView;            IGraphicsContainer pGraphicsContainer = pMap as IGraphicsContainer;

  Map类实现了IMap、IActiveView、IGraphicsContainer等等这几个接口；

在这里的A类就相当于Map类，在主函数中（即相当于客户端，完全屏蔽掉了类A），直接调用了A所接口。

这就是所谓COM组件中接口的机制。