探索MFC全局函数-AfxGetApp（）
MFC做到了从C/SDK开发Win32程序到利用OOP思想开发Win32程序的过渡，它的封装完美体现的C++的三大特性，提高了Win32程序的开发效率，但它的封装也使得本来清晰的脉络，变得晦涩起来。
今天我们探究被微软冠以Afx前缀的全局函数AfxGetApp（），这个函数作用是获取当前应用进程的指针，确切的说是获取由CWinApp派生出类的对象，相信懂MFC的人都熟知，但作为全局函数的它是如何在基类获取的派生类对象的？
现在我们开始一步一步揭开AfxGetApp（）神秘面纱~
（1）AfxGetApp（）
函数的声明在AFXWIN.H，定义在AFXWIN1.INL
_AFXWIN_INLINE CWinApp* AFXAPI AfxGetApp()
{ return afxCurrentWinApp; }
afxCurrentWinApp是一个宏，定义在AFXWIN.H中
#define afxCurrentWinApp AfxGetModuleState()->m_pCurrentWinApp
(2)AfxGetModuleState()
其返回值为AFX_MODULE_STATE类指针，声明在AFXSTAT_.H
AFX_MODULE_STATE* AFXAPI AfxGetModuleState();
定义在AFXSTATE.CPP
AFX_MODULE_STATE* AFXAPI AfxGetModuleState()
{
_AFX_THREAD_STATE* pState = _afxThreadState;
AFX_MODULE_STATE* pResult;
if (pState->m_pModuleState != NULL)
{
// thread state's module state serves as override
pResult = pState->m_pModuleState;
}
else
{
// otherwise, use global app state
pResult = _afxBaseModuleState.GetData();
}
ASSERT(pResult != NULL);
return pResult;
}
AfxGetModuleState函数的定义中，可以看出函数返回的是pState->m_pModuleState或者_afxBaseModuleState.GetData();
（3）_afxThreadState,和_afxBaseModuleState都是全局变量，上文中的pState就是_afxThreadState.
_afxThreadState声明在AFXSTAT_.H，
class _AFX_THREAD_STATE : public CNoTrackObject
{
public:
_AFX_THREAD_STATE();
virtual ~_AFX_THREAD_STATE();
// override for m_pModuleState in _AFX_APP_STATE
AFX_MODULE_STATE* m_pModuleState;//上面的pState->m_pModuleState就是这个值，存储模块状态
AFX_MODULE_STATE* m_pPrevModuleState;
// memory safety pool for temp maps
void* m_pSafetyPoolBuffer; // current buffer
// thread local exception context
AFX_EXCEPTION_CONTEXT m_exceptionContext;
// CWnd create, gray dialog hook, and other hook data
CWnd* m_pWndInit;
CWnd* m_pAlternateWndInit; // special case commdlg hooking
DWORD m_dwPropStyle;
DWORD m_dwPropExStyle;
HWND m_hWndInit;
BOOL m_bDlgCreate;
HHOOK m_hHookOldCbtFilter;
HHOOK m_hHookOldMsgFilter;
// other CWnd modal data
MSG m_lastSentMsg; // see CWnd::WindowProc
HWND m_hTrackingWindow; // see CWnd::TrackPopupMenu
HMENU m_hTrackingMenu;
TCHAR m_szTempClassName[96]; // see AfxRegisterWndClass
HWND m_hLockoutNotifyWindow; // see CWnd::OnCommand
BOOL m_bInMsgFilter;
// other framework modal data
CView* m_pRoutingView; // see CCmdTarget::GetRoutingView
CFrameWnd* m_pRoutingFrame; // see CCmdTarget::GetRoutingFrame
// MFC/DB thread-local data
BOOL m_bWaitForDataSource;
// common controls thread state
CToolTipCtrl* m_pToolTip;
CWnd* m_pLastHit; // last window to own tooltip
int m_nLastHit; // last hittest code
TOOLINFO m_lastInfo; // last TOOLINFO structure
int m_nLastStatus; // last flyby status message
CControlBar* m_pLastStatus; // last flyby status control bar
// OLE control thread-local data
CWnd* m_pWndPark; // "parking space" window
long m_nCtrlRef; // reference count on parking window
BOOL m_bNeedTerm; // TRUE if OleUninitialize needs to be called
};
EXTERN_THREAD_LOCAL(_AFX_THREAD_STATE, _afxThreadState)//_afxThreadState全局变量声明定义在AFXSTATE.CPP
THREAD_LOCAL(_AFX_THREAD_STATE, _afxThreadState)//_afxThreadState全局变量定义
_afxBaseModuleState声明定义在AFXSTATE.CPP
class _AFX_BASE_MODULE_STATE : public AFX_MODULE_STATE
{
public:
#ifdef _AFXDLL
_AFX_BASE_MODULE_STATE() : AFX_MODULE_STATE(TRUE, AfxWndProcBase, _MFC_VER)
#else
_AFX_BASE_MODULE_STATE() : AFX_MODULE_STATE(TRUE)
#endif
{ }
};
PROCESS_LOCAL(_AFX_BASE_MODULE_STATE, _afxBaseModuleState)//_afxBaseModuleState全局变量声明定义
（4）AFX_MODULE_STATE类
我们看看AFX_MODULE_STATE类中有什么？其实它包含了AfxGetApp要返回的CWinApp。
// AFX_MODULE_STATE (global data for a module)
class AFX_MODULE_STATE : public CNoTrackObject
{
public:
#ifdef _AFXDLL
AFX_MODULE_STATE(BOOL bDLL, WNDPROC pfnAfxWndProc, DWORD dwVersion);
AFX_MODULE_STATE(BOOL bDLL, WNDPROC pfnAfxWndProc, DWORD dwVersion,
BOOL bSystem);
#else
AFX_MODULE_STATE(BOOL bDLL);
#endif
~AFX_MODULE_STATE();
CWinApp* m_pCurrentWinApp;//转了好几次，终于见到庐山真面目了，没错，这就是我们从AfxGetApp获取的值。
HINSTANCE m_hCurrentInstanceHandle;
HINSTANCE m_hCurrentResourceHandle;
LPCTSTR m_lpszCurrentAppName;
BYTE m_bDLL; // TRUE if module is a DLL, FALSE if it is an EXE
BYTE m_bSystem; // TRUE if module is a "system" module, FALSE if not
BYTE m_bReserved[2]; // padding
DWORD m_fRegisteredClasses; // flags for registered window classes
// runtime class data
#ifdef _AFXDLL
CRuntimeClass* m_pClassInit;
#endif
CTypedSimpleList m_classList;
// OLE object factories
#ifndef _AFX_NO_OLE_SUPPORT
#ifdef _AFXDLL
COleObjectFactory* m_pFactoryInit;
#endif
CTypedSimpleList m_factoryList;
#endif
// number of locked OLE objects
long m_nObjectCount;
BOOL m_bUserCtrl;
// AfxRegisterClass and AfxRegisterWndClass data
TCHAR m_szUnregisterList[4096];
#ifdef _AFXDLL
WNDPROC m_pfnAfxWndProc;
DWORD m_dwVersion; // version that module linked against
#endif
// variables related to a given process in a module
// (used to be AFX_MODULE_PROCESS_STATE)
#ifdef _AFX_OLD_EXCEPTIONS
// exceptions
AFX_TERM_PROC m_pfnTerminate;
#endif
void (PASCAL *m_pfnFilterToolTipMessage)(MSG*, CWnd*);
#ifdef _AFXDLL
// CDynLinkLibrary objects (for resource chain)
CTypedSimpleList m_libraryList;
// special case for MFCxxLOC.DLL (localized MFC resources)
HINSTANCE m_appLangDLL;
#endif
#ifndef _AFX_NO_OCC_SUPPORT
// OLE control container manager
COccManager* m_pOccManager;
// locked OLE controls
CTypedSimpleList m_lockList;
#endif
#ifndef _AFX_NO_DAO_SUPPORT
_AFX_DAO_STATE* m_pDaoState;
#endif
#ifndef _AFX_NO_OLE_SUPPORT
// Type library caches
CTypeLibCache m_typeLibCache;
CTypeLibCacheMap* m_pTypeLibCacheMap;
#endif
// define thread local portions of module state
THREAD_LOCAL(AFX_MODULE_THREAD_STATE, m_thread)
};
（5）CWinApp构造函数
CWinApp* m_pCurrentWinApp;已经找到，那么它是在被赋值的呢，就是在CWinApp的构造函数，当MFC程序中CWinApp所派生的CMYWinApp（举例）类对象theApp(全局对象)被构造时，就会触动CWinApp构造函数，此时CWinApp构造函数中的this就指的是theApp，然后将this保存到m_pCurrentWinApp中。
CWinApp::CWinApp(LPCTSTR lpszAppName)
{
if (lpszAppName != NULL)
m_pszAppName = _tcsdup(lpszAppName);
else
m_pszAppName = NULL;
// initialize CWinThread state
AFX_MODULE_STATE* pModuleState = _AFX_CMDTARGET_GETSTATE();//获取全局对象指针
AFX_MODULE_THREAD_STATE* pThreadState = pModuleState->m_thread;
ASSERT(AfxGetThread() == NULL);
pThreadState->m_pCurrentWinThread = this;
ASSERT(AfxGetThread() == this);
m_hThread = ::GetCurrentThread();
m_nThreadID = ::GetCurrentThreadId();
// initialize CWinApp state
ASSERT(afxCurrentWinApp == NULL); // only one CWinApp object please
pModuleState->m_pCurrentWinApp = this;//此处就是将theApp的地址保存到m_pCurrentWinApp中
ASSERT(AfxGetApp() == this);
// in non-running state until WinMain
m_hInstance = NULL;
m_pszHelpFilePath = NULL;
m_pszProfileName = NULL;
m_pszRegistryKey = NULL;
m_pszExeName = NULL;
m_pRecentFileList = NULL;
m_pDocManager = NULL;
m_atomApp = m_atomSystemTopic = NULL;
m_lpCmdLine = NULL;
m_pCmdInfo = NULL;
// initialize wait cursor state
m_nWaitCursorCount = 0;
m_hcurWaitCursorRestore = NULL;
// initialize current printer state
m_hDevMode = NULL;
m_hDevNames = NULL;
m_nNumPreviewPages = 0; // not specified (defaults to 1)
// initialize DAO state
m_lpfnDaoTerm = NULL; // will be set if AfxDaoInit called
// other initialization
m_bHelpMode = FALSE;
m_nSafetyPoolSize = 512; // default size
}
到目前估计大家也明白了AfxGetApp（）函数实现，欢迎探讨