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;
}

 

 

 

 

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