我眼里的RuntimeClass实现

最近开始学习VC了，谈谈心得吧。班门弄斧，请多多指教。

心得之一：

MFC中RuntiemClass支持的实现：

只要是从CObject派生的类，可以轻松实现RuntiemClass支持。当然，是通过编译器提供的宏来实现的。那么其实现机制是怎样的呢？我觉得只需要四个步骤。

首先让我们简化一下CRuntiemClass和CObject的定义，抽取出与RuntiemClass相关的部分：

struct CRuntimeClass{ char m_lpszClassName[255]; int m_nObjectSize; CObject* (*m_pfnCreateObject)(); CObject* CreateObject();};

class CObject{public: virtual CRuntimeClass* GetRuntimeClass() const {return NULL;} static CRuntimeClass classCObject; virtual ~CObject(){};protected: CObject(){printf("CObject constructed/n");}};

我所说的四个步骤是（下面的操作都是对于从CObject派生的类而言的）：

1.添加CRuntiemClass类型的静态成员classCMyClass(请把CMyClass换成你的类名）

        static CRuntimeClass classCMyClass;

2.覆盖父类（即CObject)的GetRuntimeClass()方法，使之返回classCMyClass的指针

3.添加并实现 CreateObject();方法。

  声明： static CObject* CreateObject();

  实现：CObject* CMyClass::CreateObject() { return new CMyClass;  }

4.为classCMyClass赋值。使m_lpszClassName="CMyClass";

    m_nObjectSize=sizeof (CMyClass);

     函数指针m_pfnCreateObject指向CMyClass::CreateObject。

       CRuntimeClass CMyClass::classCMyClass=   {"CMyClass",sizeof (CMyClass),                                                                        CMyClass::CreateObject};

附上完整的例程（摘自Programming Visual C++6.0 Unleashed)：

#include <stdio.h>#define RUNTIME_CLASS(class_name) (&class_name::class##class_name)

class CObject;struct CRuntimeClass{ char m_lpszClassName[21]; int m_nObjectSize; CObject* (*m_pfnCreateObject)(); CObject* CreateObject();};

class CObject{public: virtual CRuntimeClass* GetRuntimeClass() const {return NULL;} static CRuntimeClass classCObject; virtual ~CObject(){};protected: CObject(){printf("CObject constructed/n");}};

CRuntimeClass CObject::classCObject=    {"CObject",sizeof(CObject),NULL};

CObject* CRuntimeClass::CreateObject(){ return (*m_pfnCreateObject)();}

class CAlpha:public CObject{public: virtual CRuntimeClass* GetRuntimeClass() const {  return &classCAlpha; } static CRuntimeClass classCAlpha; static CObject* CreateObject();protected: CAlpha(){printf("CAlpha constructor/n");}};

CRuntimeClass CAlpha::classCAlpha={"CAlpha",sizeof(CAlpha),CAlpha::CreateObject};

CObject* CAlpha::CreateObject(){ return new CAlpha;}

class CBeta:public CObject{public: virtual CRuntimeClass* GetRuntimeClass() const {return &classCBeta;} static CRuntimeClass classCBeta; static CObject* CreateObject();protected: CBeta(){printf("CBeta constructed/n");}};   CRuntimeClass CMyClass::classCMyClass=   {"CMyClass",sizeof (CMyClass),    CMyClass::CreateObject};

 

CRuntimeClass CBeta::classCBeta={"CBeata",sizeof(CBeta),CBeta::CreateObject};

CObject* CBeta::CreateObject(){ return new CBeta;}

class CGama:public CObject{public: virtual CRuntimeClass* GetRuntimeClass() const { return &classCGama;} static CRuntimeClass classCGama; static CObject* CreateObject();protected: CGama(){printf("CGama constructed/n");}};

CRuntimeClass CGama::classCGama={"CGama",sizeof(CGama),CGama::CreateObject};

CObject* CGama::CreateObject(){ return new CGama();}

int main(){ printf("Entering dynCreate main/n");

 CRuntimeClass* pRTCAlpha=RUNTIME_CLASS(CAlpha); CObject* pObj1=pRTCAlpha->CreateObject(); printf("class of pObj1=%s/n",pObj1->GetRuntimeClass()->m_lpszClassName);  CRuntimeClass* pRTCBeta=RUNTIME_CLASS(CBeta); CObject* pObj2=pRTCBeta->CreateObject(); printf("class of pObj2=%s/n",pObj2->GetRuntimeClass()->m_lpszClassName);

 CRuntimeClass* pRTCGama=RUNTIME_CLASS(CGama); CObject* pObj3=pRTCGama->CreateObject(); printf("class of pObj3=%s/n",pObj3->GetRuntimeClass()->m_lpszClassName);

  delete pObj1; delete pObj2; delete pObj3;

 return 0;}