5.MFC运行时动态创建

在看这篇博客时如果你对MFC的RTTI还不了解，建议看我的前一篇博客/article/10898036.html

相对于前一篇将的运行时识别类型信息，动态创建只是在原来基础上做了一些改动而已。

程序的运行结果： CFrameWnd， CView 使用的动态创建宏

struct CRuntimeClass
{
LPCSTR m_lpszClassName; //类的名字
int m_nObjectSize; //类的大小
UINT m_wSchema; //shema number of the loaded class
CObject* (PASCAL* m_pfnCreateObject)(); //NULL=> abstract class,一个指向非空的函数指针
CRuntimeClass* m_pBaseClass;//表示 基类的 CRuntimeClass
//调用 m_pfnCreateObject 来创建 对象

CObject* CreateObjct();
//通过类名获取对应的CRuntimeClas*
static CRuntimeClass* PASCAL Load(const char* classname);

static CRuntimeClass* pFirstClass;// 类链表的头指针
CRuntimeClass* m_pNextClass;// 用来构建和访问类链表

};

增加了两个新成员

//调用 m_pfnCreateObject 来创建 对象

CObject* CreateObjct();
//通过类名获取对应的CRuntimeClas*
static CRuntimeClass* PASCAL Load(const char* classname);

宏也又了一些改变

#define DECLARE_DYNCREATE(class_name)\
DECLARE_DYNAMIC(class_name)\
static CObject* PASCAL CreateObject();//增加了创建对象的函数

#define IMPLEMENT_DYNCREATE(class_name, base_class_name)\
CObject* PASCAL class_name::CreateObject()\
{ return new class_name; }\
_IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, 0xffff, class_name::CreateObject)

在类中使用时也改成使用 新的两个宏 DECLARE_DYNCREATE IMPLEMENT_DYNCREATE 分别写在头文件和实现文件中
MFC.cpp

#pragma once

#include<iostream>
using namespace std;

class CObject;
#define BOOL int
#define TRUE 1
#define FLASE 0
#define LPCSTR const char*
#define LPSTR char*s
#define UINT int
#define PASCAL __stdcall
struct CRuntimeClass
{
LPCSTR m_lpszClassName; //类的名字
int m_nObjectSize; //类的大小
UINT m_wSchema; //shema number of the loaded class
CObject* (PASCAL* m_pfnCreateObject)(); //NULL=> abstract class,一个指向非空的函数指针
CRuntimeClass* m_pBaseClass;//表示 基类的 CRuntimeClass
//调用 m_pfnCreateObject 来创建 对象

CObject* CreateObjct();
//通过类名获取对应的CRuntimeClas*
static CRuntimeClass* PASCAL Load(const char* classname);

static CRuntimeClass* pFirstClass;// 类链表的头指针
CRuntimeClass* m_pNextClass;// 用来构建和访问类链表

};
struct AFX_CLASSINIT
{
AFX_CLASSINIT(CRuntimeClass* pNewClass);
};
//
#define RUNTIME_CLASS(class_name)\
(&class_name::class##class_name)
//声明定义的宏
#define DECLARE_DYNAMIC(class_name)\
public:\
static CRuntimeClass class##class_name; \
virtual CRuntimeClass* GetRuntimeClass() const;

//实现定义的宏, 宏中使用一个 # 表示 用引号括起后面的内容 "class_name", 两个引号表示连接
#define _IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, wSchema, pfnNew)\
static char _lpsz##class_name[] = #class_name; \
CRuntimeClass class_name::class##class_name = { \
_lpsz##class_name, sizeof(class_name), wSchema, pfnNew, \
RUNTIME_CLASS(base_class_name), NULL }; \
static AFX_CLASSINIT _init_##class_name(&class_name::class##class_name); \
CRuntimeClass* class_name::GetRuntimeClass() const \
{ return &class_name::class##class_name; } \

#define DECLARE_DYNCREATE(class_name)\
DECLARE_DYNAMIC(class_name)\
static CObject* PASCAL CreateObject();//增加了创建对象的函数

#define IMPLEMENT_DYNAMICLASS(class_name, base_class_name)\
_IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, 0xffff, NULL)

#define IMPLEMENT_DYNCREATE(class_name, base_class_name)\
CObject* PASCAL class_name::CreateObject()\
{ return new class_name; }\
_IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, 0xffff, class_name::CreateObject)
class CObject
{
public:
CObject::CObject(){}
CObject::~CObject(){}

virtual CRuntimeClass* GetRuntimeClass() const;
BOOL IsKindOf(const CRuntimeClass* pClass) const;
public:
static CRuntimeClass classCObject;

};

class CCmdTarget :public CObject
{
DECLARE_DYNAMIC(CCmdTarget)
/*
#define DECLARE_DYNAMIC(CCmdTarget)\
public:\
static CRuntimeClass class##CCmdTarget; \
virtual CRuntimeClass* GetRuntimeClass() const;
*/
public:
CCmdTarget::CCmdTarget(){}
CCmdTarget::~CCmdTarget(){}

};

class CWinThread : public CCmdTarget
{
DECLARE_DYNAMIC(CWinThread)
public:

virtual bool InitInstance()
{
cout << "CWinThread:InitInstance \n";
return true;
}

virtual int Run()
{
cout << "CWinThread:Run \n";
return 1;
}

};

//先声音 CWnd类 因为在 CWinApp中需要用到，但是却没有 实际定义 CWnd这个类
class CWnd;

class CWinApp : public CWinThread
{
DECLARE_DYNAMIC(CWinApp)
public:
CWinApp* m_pCurrentWinApp;
CWnd* m_pMainWnd;
public:
CWinApp::CWinApp()
{
m_pCurrentWinApp = this;

}

virtual bool InitInstance()
{
cout << "CWinApp:InitInstance \n";
return true;
}

virtual int Run()
{
cout << "CWinApp:Run \n";
return CWinThread::Run();
}

virtual bool InitApplication()
{
cout << "CWinApp:InitApplication \n";
return true;
}

};

class CDocument : public CCmdTarget
{
DECLARE_DYNAMIC(CDocument)
public:
CDocument::CDocument(){}
CDocument::~CDocument(){}
};

class CWnd : public CCmdTarget
{
DECLARE_DYNAMIC(CWnd)
public:
virtual bool Create();
bool CreateEx();
virtual bool PreCreateWindow();

};

class CView : public CWnd
{
DECLARE_DYNCREATE(CView)
public:
CView::CView(){}
CView::~CView(){}
};

class CFrameWnd : public CWnd
{
DECLARE_DYNCREATE(CFrameWnd)
public:
CFrameWnd::CFrameWnd(){}
CFrameWnd::~CFrameWnd(){}
bool Create();
virtual bool PreCreateWindow();
};

CWinApp* AfxGetApp();

MFC.cpp 文件中主要观察 CRuntimeClass 新增的两个函数 CreatObject, Load

#include "MFC.h"

static char lpszObject[] = "CObject";
//作为链表的尾节点。CObject 有一些特殊，其没有基类
struct CRuntimeClass CObject::classCObject = {
lpszObject, sizeof(CObject), 0xffff, NULL, NULL, NULL
};

static AFX_CLASSINIT _initCObject(&CObject::classCObject);
//静态类成员必须，在实现文件中定义才可以使用
CRuntimeClass* CRuntimeClass::pFirstClass = NULL;

//将节点连接起来
AFX_CLASSINIT::AFX_CLASSINIT(CRuntimeClass* pNewClass)
{
pNewClass->m_pNextClass = CRuntimeClass::pFirstClass;
CRuntimeClass::pFirstClass = pNewClass;
}

CRuntimeClass* CObject::GetRuntimeClass() const
{
//返回这个类的 运行时类
return &CObject::classCObject;
}

BOOL CObject::IsKindOf(const CRuntimeClass* pClass) const
{
CRuntimeClass* pClassThis = GetRuntimeClass();
while (pClassThis != NULL)
{
if (pClassThis == pClass)
return TRUE;
pClassThis = pClassThis->m_pBaseClass;
}
return false;
}

///////////////Create Load
CObject* CRuntimeClass::CreateObjct()
{
if (m_pfnCreateObject == NULL)
{
printf("Error: Trying to Create object which is not DECLARE_DYNCREATE \n");
return NULL;
}

CObject* pObject = NULL;
pObject = (*m_pfnCreateObject)();
return pObject;
}

CRuntimeClass*  CRuntimeClass::Load(const char* classname)
{
CRuntimeClass *pClass = NULL;
for (pClass = CRuntimeClass::pFirstClass; pClass != NULL; pClass = pClass->m_pNextClass)
{
if (strcmp(classname, pClass->m_lpszClassName) == 0)
{
return pClass;
}
}
cout << "Error: Class not found: " << classname << endl;
return NULL;
}

IMPLEMENT_DYNAMICLASS(CCmdTarget, CObject)

//可以看一下替换后的结果
/*
//我们暂时先不管0xffff, NULL 这两个参数
#define IMPLEMENT_DYNAMICLASS(CCmdTarget, CObject)\
_IMPLEMENT_RUNTIMECLASS(CCmdTarget, CObject, 0xffff, NULL)

#define _IMPLEMENT_RUNTIMECLASS(CCmdTarget, CObject, wSchema, pfnNew)\
static char _lpszCCmdTarget[] = "CCmdTarget"; \为类创建一个字符串名称
CRuntimeClass CCmdTarget::classCCmdTarget = { \初始化类的静态成员变量，CRuntimeClass ，类的静态成员变量必须在使用前初始化
_lpszCCmdTarget, sizeof(CCmdTarget), wSchema, pfnNew, \//这里对照结构体一一赋值
RUNTIME_CLASS(CObject), NULL }; \
static AFX_CLASSINIT _init_CCmdTarget(&class_name::classCCmdTarget); \ //先留着 这部分还没有用到
CRuntimeClass* CCmdTarget::GetRuntimeClass() const \
{ return &class_name::classCCmdTarget; } \

*/

IMPLEMENT_DYNAMICLASS(CWinThread, CCmdTarget)
IMPLEMENT_DYNAMICLASS(CWinApp, CWinThread)
IMPLEMENT_DYNAMICLASS(CWnd, CCmdTarget)
IMPLEMENT_DYNCREATE(CFrameWnd, CWnd)
IMPLEMENT_DYNAMICLASS(CDocument, CCmdTarget)
IMPLEMENT_DYNCREATE(CView, CWnd)

bool CWnd::Create()
{
return true;
}

bool CWnd::CreateEx()
{
//由于PreCrete是虚函数，所以PreCreateWindow属于那个类根据this指针决定
PreCreateWindow();
return true;
}

bool CWnd::PreCreateWindow()
{
return true;
}

bool CFrameWnd::Create()
{
//必然是基类的CraeteEx 因为CFrameWnd没有重写
CreateEx();
return true;
}

bool CFrameWnd::PreCreateWindow()
{
return true;
}

void PrintAllClasses()
{
CRuntimeClass* pClass;

for (pClass = CRuntimeClass::pFirstClass; pClass != NULL; pClass = pClass->m_pNextClass)
{
cout << "ClassName: " << pClass->m_lpszClassName << endl;
cout << "ClassSize: " << pClass->m_nObjectSize << endl;
cout << "ClassSchema: " << pClass->m_wSchema << endl;
cout << endl;
}

}

void main()
{

PrintAllClasses();

CRuntimeClass *pClassRef = NULL;
CObject *pObj = NULL;
char name[64] = { 0 };
while (1)
{

cin >> name;
pClassRef = CRuntimeClass::Load(name);
if (pClassRef == NULL)
break;
pObj = pClassRef->CreateObjct();
if (pObj != NULL)
{
cout << "create success \n";
}
}

system("pause");
}