近來(lái)在論壇上很有多帖子問(wèn)到如何使用DLL中的資源(包括對(duì)話框，圖標(biāo)等)的問(wèn)題，現(xiàn)在筆者就來(lái)就此問(wèn)題談?wù)?#xff0c;包含在DLL內(nèi)部使用資源，DLL中使用其它DLL中的資源和在應(yīng)用程序中使用資源。

?????? 我們先以圖標(biāo)為例說(shuō)起(其它的資源與此圖標(biāo)的加載原理大致相同)，我們要加載圖標(biāo)，一般是調(diào)用AfxGetApp()->LoadIcon(…)；下面是CWinApp::LoadIcon的實(shí)現(xiàn)(afxwin2.inl)：

_AFXWIN_INLINE HICON CWinApp::LoadIcon(LPCTSTR lpszResourceName) const

{ return ::LoadIcon(AfxFindResourceHandle(lpszResourceName,

???????? RT_GROUP_ICON), lpszResourceName); }

_AFXWIN_INLINE HICON CWinApp::LoadIcon(UINT nIDResource) const

{ return ::LoadIcon(AfxFindResourceHandle(MAKEINTRESOURCE(nIDResource),

???????? RT_GROUP_ICON), MAKEINTRESOURCE(nIDResource)); }

?????? 可以看到CWinApp::LoadIcon實(shí)際上調(diào)用了API .LoadIcon,下面是API　LoadIcon的原型：

HICON?LoadIcon(??????HINSTANCE?hInstance,????LPCTSTR?lpIconName);

?

hInstance

[in]?Handle to an instance of the module whose executable file contains the icon to be loaded. This parameter must be NULL when a standard icon is being loaded.

hInstance是我們要加載ICON的模塊實(shí)例，這個(gè)實(shí)例從何來(lái)，當(dāng)然我們可以直接傳入DLL的實(shí)例，對(duì)于通過(guò)LoadLibrary動(dòng)態(tài)加載的DLL我們可以很容易的得到其句柄，但對(duì)于我們直接鏈接的DLL得到其句柄則要費(fèi)一番周折。可以看到CWinApp::LoadIcon是通過(guò)AfxFindResouceHandle找到此句柄的。下面是AfxFindResourceHandle的定義(afxwin.h)：

#ifndef _AFXDLL

#define AfxFindResourceHandle(lpszResource, lpszType) AfxGetResourceHandle()

#else

HINSTANCE AFXAPI AfxFindResourceHandle(LPCTSTR lpszName, LPCTSTR lpszType);

#endif

?????? 我們先討論在靜態(tài)鏈接庫(kù)中使用MFC　DLL的情況。可以看到，我們?nèi)绻陟o態(tài)庫(kù)中使用MFC　DLL的話(#ifndef _AFXDLL),實(shí)際上就是調(diào)用的AfxGetResourceHandle，MSDN中的說(shuō)明是

AfxGetResourceHandle??

This function accesses the application’s resources directly by using the?HINSTANCE?handle returned, for example, in calls to the Windows function?FindResource.

HINSTANCE AfxGetResourceHandle( );

Return Value

An?HINSTANCE?handle where the default resources of the application are loaded.

函數(shù)返回的應(yīng)用程序加載的缺省資源的HINSTANCE句柄,HINSTANCE相當(dāng)于HMODULE，也就是資源所在的模塊句柄。顯然在此，我們使用的是DLL中的資源，那么我們就應(yīng)該返回此DLL中的HINSTANCE了，如果讓AfxGetResourceHandle返回DLL的HINSTANCE呢？答案是通過(guò)AfxSetResourceHandle設(shè)置。MSDN中AfxSetResouceHandle的說(shuō)明如下：

AfxSetResourceHandle

This function sets the?HINSTANCE?handle that determines where the default resources of the application are loaded.

void AfxSetResourceHandle(

HINSTANCE?hInstResource?);

Parameters

hInstResource

Specifies the instance or module handle to an .EXE or DLL file from which the application’s resources are loaded.

我們只需將DLL的HINSTANCE傳入AfxSetResouceHanle就行了。如何得到DLL的HINSTANCE呢，我們可以通過(guò)DLL聲明一個(gè)接口HINSTANCE GetInstance獲得，也可以通過(guò)EnumProcessMoudules找到（詳細(xì)的過(guò)程見(jiàn)MSDN中EnumProcessModules的說(shuō)明和示例）。

我們使用完DLL中的資源要使用EXE中的資源的資源怎么辦呢？我們需要在使用完成后用AfxSetResource重新將資源模塊的句柄設(shè)置為原來(lái)的值，如果來(lái)保證在資源使用完成后完成這一個(gè)工作呢，即使在使用過(guò)程中發(fā)生異常了，為此我們利C++類的構(gòu)造和析構(gòu)機(jī)制創(chuàng)建了這一類：

class CLocalResource?

{

public:

???????? CLocalResource(HINSTANCE hInstance)

{

???????? m_hInstOld=AfxGetInstanceHandle();

???????? AfxSetInstanceHandle(hInstance);

}

???????? virtual ~CLocalResource()

{

???????? AfxSetInstanceHandle(m_hInstOld);

}

protected:

???????? HINSTANCE m_hInstOld;

};

???????? 我們只需在使用DLL的資源之前構(gòu)造一個(gè)CLocalInstance就行了。

void CXXXX::LoadResouceFromDLL(HINSTANCE hInst,UINT nResID,…)

{

???????? CLocalResouce localRes(hInst);

???????? …

}

下面來(lái)討論在動(dòng)態(tài)庫(kù)中使用MFC DLL的情況(也就是定義了_AFXDLL的情況)

來(lái)看看AfxGetInstanceHandle ,AfxGetResourceHandle和AfxSetResouceHandle的實(shí)現(xiàn)(afxwin1.inl中)：

_AFXWIN_INLINE HINSTANCE AFXAPI AfxGetInstanceHandle()

???????? { ASSERT(afxCurrentInstanceHandle != NULL);

???????? return afxCurrentInstanceHandle; }

_AFXWIN_INLINE HINSTANCE AFXAPI AfxGetResourceHandle()

{ ASSERT(afxCurrentResourceHandle != NULL);

return afxCurrentResourceHandle; }

_AFXWIN_INLINE void AFXAPI AfxSetResourceHandle(HINSTANCE hInstResource)

{ ASSERT(hInstResource != NULL); afxCurrentResourceHandle = hInstResource; }

實(shí)際上訪問(wèn)的就是afxCurrentInstanceHandle,afxCurrentResourceHandle。

/

// Global functions for access to the one and only CWinApp

…

#define afxCurrentInstanceHandle??? AfxGetModuleState()->m_hCurrentInstanceHandle

#define afxCurrentResourceHandle?? AfxGetModuleState()->m_hCurrentResourceHandle

….

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;

}

其中的_AFX_THREAD_STATE在此我們就不討論了，有興趣的讀者可以閱讀(afxstat_.h和afxstate.cpp)。

???????? 那AfxGetModuleState()->m_hCurrentResourceHandle又是在哪初始化的呢？

我們可以在appinit.cpp中的BOOL AFXAPI AfxWinInit(HINSTANCE hInstance, HINSTANCE hPrevInstance,LPTSTR lpCmdLine, int nCmdShow)看到

// set resource handles

???????? AFX_MODULE_STATE* pModuleState = AfxGetModuleState();

???????? pModuleState->m_hCurrentInstanceHandle = hInstance;

???????? pModuleState->m_hCurrentResourceHandle = hInstance;

?????? 和appinit.cpp中的void CWinApp::SetCurrentHandles()中看到

???????? AFX_MODULE_STATE* pModuleState = _AFX_CMDTARGET_GETSTATE();

???????? pModuleState->m_hCurrentInstanceHandle = m_hInstance;

???????? pModuleState->m_hCurrentResourceHandle = m_hInstance;

???????? CWinApp::SetCurrentHandles()也是由AfxWinInit調(diào)用的，那AfxWinInit又由誰(shuí)調(diào)用呢？

我們可以在DllMain(dllinit.cpp和dllmodul.cpp，分別對(duì)應(yīng)于MFC擴(kuò)展DLL和MFC規(guī)則DLL)看到

(dllinit.cpp,MFC擴(kuò)展DLL)

static AFX_EXTENSION_MODULE coreDLL;

….

extern "C"

BOOL WINAPI DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID)

{

???????? if (dwReason == DLL_PROCESS_ATTACH)

???????? {

?????????????????? …….

?????????????????? // initialize this DLL's extension module

?????????????????? VERIFY(AfxInitExtensionModule(coreDLL, hInstance));

#ifdef _AFX_OLE_IMPL

?????????????????? AfxWinInit(hInstance, NULL, _T(""), 0);

?

?????????????????? ….

#endif

….

?????????????????? // wire up this DLL into the resource chain

?????????????????? CDynLinkLibrary* pDLL = new CDynLinkLibrary(coreDLL, TRUE);

?????????????????? ASSERT(pDLL != NULL);

?????????????????? pDLL->m_factoryList.m_pHead = NULL;

?????????????????? ….

???????? }

???????? else if (dwReason == DLL_PROCESS_DETACH)

???????? {

?????????????????? ….

?????????????????? // cleanup module state for this process

?????????????????? AfxTermExtensionModule(coreDLL);

?????????????????? ….

?????????????????? // cleanup module state in OLE private module state

?????????????????? AfxTermExtensionModule(coreDLL, TRUE);

?????????????????? ….

???????? }

???????? …

}

可以看到在提供自動(dòng)化支持時(shí)，將調(diào)用AfxWinInit(但MFC的DLL向?qū)?#xff0c;對(duì)于擴(kuò)展DLL卻不允許添加自動(dòng)化支持)。

(在dllmodul.cpp中，MFC常規(guī)DLL)

#ifdef _AFXDLL

static AFX_EXTENSION_MODULE controlDLL;

….

#endif

?

extern "C"

BOOL WINAPI DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID /*lpReserved*/)

{

???????? if (dwReason == DLL_PROCESS_ATTACH)

???????? {

….

?????????????????? _AFX_THREAD_STATE* pState = AfxGetThreadState();

?????????????????? AFX_MODULE_STATE* pPrevModState = pState->m_pPrevModuleState;

?

?????????????????? // Initialize DLL's instance(/module) not the app's

?????????????????? if (!AfxWinInit(hInstance, NULL, _T(""), 0))

?????????????????? {

??????????????????????????? AfxWinTerm();

??????????????????????????? goto Cleanup;?????? // Init Failed

?????????????????? }

?

?????????????????? ….

#ifdef _AFXDLL

?????????????????? // wire up this DLL into the resource chain

?????????????????? VERIFY(AfxInitExtensionModule(controlDLL, hInstance));

?????????????????? CDynLinkLibrary* pDLL; pDLL = new CDynLinkLibrary(controlDLL);

?????????????????? ASSERT(pDLL != NULL);

#else

?????????????????? AfxInitLocalData(hInstance);

#endif

…

???????? }

???????? else if (dwReason == DLL_PROCESS_DETACH)

???????? {

….

#ifdef _AFXDLL

?????????????????? AfxTermExtensionModule(controlDLL, TRUE);

#else

?????????????????? AfxTermLocalData(hInstance, TRUE);

#endif

???????? }

???????? …

}

???????? 看到上面的代碼，其實(shí)與MFC擴(kuò)展DLL的代碼大同小異，只過(guò)是MFC常規(guī)DLL可以支持在靜態(tài)鏈接庫(kù)全用MFC DLL，相應(yīng)的初始化/反初始化函數(shù)就變?yōu)榱薃fxInitLocalData/ AfxTermLocalData,在此我們不對(duì)在靜態(tài)鏈接庫(kù)中使用MFC DLL的情況作更多討論。

以及在winmain.cpp中的int AFXAPI AfxWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,LPTSTR lpCmdLine, int nCmdShow),在appmodul.cpp中我們可以看到入口函數(shù)的實(shí)現(xiàn)：

extern "C" int WINAPI

_tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,

???????? LPTSTR lpCmdLine, int nCmdShow)

{

???????? // call shared/exported WinMain

???????? return AfxWinMain(hInstance, hPrevInstance, lpCmdLine, nCmdShow);

}

看看AfxInitExtensionModule , AfxTermExtensionModule CDynLinkLibrary的定義(afxdll_.h)和實(shí)現(xiàn)(在dllinit.cpp中)就明白了DllMain做了什么：

?

BOOL AFXAPI AfxInitExtensionModule(AFX_EXTENSION_MODULE& state, HMODULE hModule)

{

???????? // only initialize once

???????? if (state.bInitialized)

???????? {

?????????????????? AfxInitLocalData(hModule);

?????????????????? return TRUE;

???????? }

???????? state.bInitialized = TRUE;

???????? // save the current HMODULE information for resource loading

???????? ASSERT(hModule != NULL);

???????? state.hModule = hModule;

???????? state.hResource = hModule;

???????? // save the start of the runtime class list

???????? AFX_MODULE_STATE* pModuleState = AfxGetModuleState();

???????? state.pFirstSharedClass = pModuleState->m_classList.GetHead();

???????? pModuleState->m_classList.m_pHead = pModuleState->m_pClassInit;

?

#ifndef _AFX_NO_OLE_SUPPORT

???????? // save the start of the class factory list

???????? state.pFirstSharedFactory = pModuleState->m_factoryList.GetHead();

???????? pModuleState->m_factoryList.m_pHead = pModuleState->m_pFactoryInit;

#endif

???????? return TRUE;

}

…

void AFXAPI AfxTermExtensionModule(AFX_EXTENSION_MODULE& state, BOOL bAll)

{

???????? // make sure initialized

???????? if (!state.bInitialized)

?????????????????? return;

?

???????? // search for CDynLinkLibrary matching state.hModule and delete it

???????? ASSERT(state.hModule != NULL);

???????? AFX_MODULE_STATE* pModuleState = AfxGetModuleState();

???????? AfxLockGlobals(CRIT_DYNLINKLIST);

???????? for (CDynLinkLibrary* pDLL = pModuleState->m_libraryList; pDLL != NULL; )

???????? {

?????????????????? CDynLinkLibrary* pNextDLL = pDLL->m_pNextDLL;

?????????????????? if (bAll || pDLL->m_hModule == state.hModule)

??????????????????????????? delete pDLL;??? // will unwire itself

?????????????????? pDLL = pNextDLL;

???????? }

???????? AfxUnlockGlobals(CRIT_DYNLINKLIST);

???????? // delete any local storage attached to this module

???????? AfxTermLocalData(state.hModule, TRUE);

???????? // remove any entries from the CWnd message map cache

???????? AfxResetMsgCache();

}

?

class CDynLinkLibrary : public CCmdTarget

{

???????? DECLARE_DYNAMIC(CDynLinkLibrary)

public:

?

// Constructor

???????? explicit CDynLinkLibrary(AFX_EXTENSION_MODULE& state, BOOL bSystem = FALSE);

???????? CDynLinkLibrary(HINSTANCE hModule, HINSTANCE hResource);

?

// Attributes

???????? HMODULE m_hModule;

???????? HMODULE m_hResource;??????????????? // for shared resources

???????? ….

???????? BOOL m_bSystem;???????????????????? // TRUE only for MFC DLLs

// Implementation

public:

???????? CDynLinkLibrary* m_pNextDLL;??????? // simple singly linked list

???????? virtual ~CDynLinkLibrary();

….

};

?

CDynLinkLibrary::CDynLinkLibrary(AFX_EXTENSION_MODULE& state, BOOL bSystem)

{

…

???????? // copy info from AFX_EXTENSION_MODULE struct

???????? ASSERT(state.hModule != NULL);

???????? m_hModule = state.hModule;

???????? m_hResource = state.hResource;

???????? m_classList.m_pHead = state.pFirstSharedClass;

….

???????? m_bSystem = bSystem;

????????

// insert at the head of the list (extensions will go in front of core DLL)

???????? DEBUG_ONLY(m_pNextDLL = NULL);

???????? AfxLockGlobals(CRIT_DYNLINKLIST);

???????? m_pModuleState->m_libraryList.AddHead(this);

???????? AfxUnlockGlobals(CRIT_DYNLINKLIST);

}

?

CDynLinkLibrary::CDynLinkLibrary(HINSTANCE hModule, HINSTANCE hResource)

{

…

???????? m_hModule = hModule;

???????? m_hResource = hResource;

???????? m_classList.m_pHead = NULL;

???????? …

???????? m_bSystem = FALSE;

???????? // insert at the head of the list (extensions will go in front of core DLL)

???????? DEBUG_ONLY(m_pNextDLL = NULL);

???????? AfxLockGlobals(CRIT_DYNLINKLIST);

???????? m_pModuleState->m_libraryList.AddHead(this);

???????? AfxUnlockGlobals(CRIT_DYNLINKLIST);

}

…

CDynLinkLibrary::~CDynLinkLibrary()

{

???????? // remove this frame window from the list of frame windows

???????? AfxLockGlobals(CRIT_DYNLINKLIST);

???????? m_pModuleState->m_libraryList.Remove(this);

???????? AfxUnlockGlobals(CRIT_DYNLINKLIST);

}

?????? 由此我們可以看出DLL初始化時(shí)先調(diào)AfxInitExtensionModule是為了構(gòu)造一個(gè)AFX_EXTENSION_MODULE,然后將它插入插入一個(gè)AFX_MODULE_STATE鏈表中,同時(shí)將當(dāng)前DLL的HINSTANCE插入此AFX_MODULE_STATE的CDynLinkLibrary鏈表中，以便稍后講到的AfxFindResourceHandle找到。DLL從內(nèi)存移出時(shí)就從此鏈表中刪除自己。

讓我們來(lái)看看AfxFindResourceHandle的實(shí)現(xiàn)(dllinit.cpp)：

HINSTANCE AFXAPI AfxFindResourceHandle(LPCTSTR lpszName, LPCTSTR lpszType)

{

???????? ASSERT(lpszName != NULL);

???????? ASSERT(lpszType != NULL);

?

???????? HINSTANCE hInst;

?

???????? // first check the main module state

???????? AFX_MODULE_STATE* pModuleState = AfxGetModuleState();

???????? if (!pModuleState->m_bSystem)

???????? {

?????????????????? hInst = AfxGetResourceHandle();

?????????????????? if (::FindResource(hInst, lpszName, lpszType) != NULL)

??????????????????????????? return hInst;

???????? }

?

???????? // check for non-system DLLs in proper order

???????? AfxLockGlobals(CRIT_DYNLINKLIST);

???????? CDynLinkLibrary* pDLL;

???????? for (pDLL = pModuleState->m_libraryList; pDLL != NULL;

?????????????????? pDLL = pDLL->m_pNextDLL)

???????? {

?????????????????? if (!pDLL->m_bSystem && pDLL->m_hResource != NULL &&

??????????????????????????? ::FindResource(pDLL->m_hResource, lpszName, lpszType) != NULL)

?????????????????? {

??????????????????????????? // found it in a DLL

??????????????????????????? AfxUnlockGlobals(CRIT_DYNLINKLIST);

??????????????????????????? return pDLL->m_hResource;

?????????????????? }

???????? }

???????? AfxUnlockGlobals(CRIT_DYNLINKLIST);

?

???????? // check language specific resource next

???????? hInst = pModuleState->m_appLangDLL;

???????? if (hInst != NULL && ::FindResource(hInst, lpszName, lpszType) != NULL)

?????????????????? return hInst;

?

???????? // check the main system module state

???????? if (pModuleState->m_bSystem)

???????? {

?????????????????? hInst = AfxGetResourceHandle();

?????????????????? if (::FindResource(hInst, lpszName, lpszType) != NULL)

??????????????????????????? return hInst;

???????? }

?

???????? // check for system DLLs in proper order

???????? AfxLockGlobals(CRIT_DYNLINKLIST);

???????? for (pDLL = pModuleState->m_libraryList; pDLL != NULL; pDLL = pDLL->m_pNextDLL)

???????? {

?????????????????? if (pDLL->m_bSystem && pDLL->m_hResource != NULL &&

??????????????????????????? ::FindResource(pDLL->m_hResource, lpszName, lpszType) != NULL)

?????????????????? {

??????????????????????????? // found it in a DLL

??????????????????????????? AfxUnlockGlobals(CRIT_DYNLINKLIST);

??????????????????????????? return pDLL->m_hResource;

?????????????????? }

???????? }

???????? AfxUnlockGlobals(CRIT_DYNLINKLIST);

?

???????? // if failed to find resource, return application resource

???????? return AfxGetResourceHandle();

}

上面的代碼首先檢查主模塊的狀態(tài),通過(guò)返回的是個(gè)AFX_MODULE_STATE的類對(duì)象指針. AFX_MODULE_STATE又是個(gè)什么呢？下面看看AFX_MODULE_STATE的定義(afxstat_.h中,它的實(shí)現(xiàn)在afxstate.cpp中，有興趣的讀者可以讀讀)：

// 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,

?????????????????? BOOL bSystem = FALSE);

#else

???????? explicit AFX_MODULE_STATE(BOOL bDLL);

#endif

???????? ~AFX_MODULE_STATE();

?

???????? CWinApp* m_pCurrentWinApp;

???????? 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

???????? …

?

#ifdef _AFXDLL

???????? // CDynLinkLibrary objects (for resource chain)

???????? CTypedSimpleList<CDynLinkLibrary*> m_libraryList;

?

???????? // special case for MFC71XXX.DLL (localized MFC resources)

???????? HINSTANCE m_appLangDLL;

#endif

….

};

我們來(lái)看看我們關(guān)心的屬性

CWinApp* m_pCurrentWinApp;

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

…

// CDynLinkLibrary objects (for resource chain)

CTypedSimpleList<CDynLinkLibrary*> m_libraryList;

?

// special case for MFC71XXX.DLL (localized MFC resources)

HINSTANCE m_appLangDLL;

看了相關(guān)注釋，也就明白什么意思了，在此就不多解釋了。

?

如果當(dāng)前主模塊是系統(tǒng)模塊(通過(guò)m_bSystem標(biāo)識(shí))，并且從當(dāng)前模塊中找到了相應(yīng)的資源就返回此模塊的HINSTANCE。接下來(lái)當(dāng)前模塊所載的DLL鏈表中的所有用戶模塊中查找，本地化的MFC資源DLL中查找，系統(tǒng)DLL中查找。如果都找不到則從EXE(或者通過(guò)AfxSetResouceHandle中設(shè)置的HINSTANCE)中查找。

如果不考慮DLL鏈表，則需要我們每次使用DLL中的資源前調(diào)用AfxSetResouceHandle，使用后再調(diào)用AfxSetResourceHandle，就同前面講的在靜態(tài)鏈接庫(kù)中使用MFC　DLL一樣。麻不麻煩？

怎么解決呢？解決方法是用資源DLL的HINSTANCE構(gòu)造一CDynLinkLibrary對(duì)象插入主模塊(EXE)的AFX_MODULE_STATE的m_libraryList中。怎么做？

看了上面DllMain的實(shí)現(xiàn)代碼，我們可以照著做。

static AFX_EXTENSION_MODULE ResouceDLL = { NULL, NULL }

BOOL CXApp::InitInstance()

{

// Get the resource DLL instance

???????? if (!AfxInitExtensionModule(ResouceDLL, hResourceModule))

???????? ???????? return 0;

new CDynLinkLibrary(ResouceDLL);??

…

}

int CGenericMFCApp::ExitInstance()

{

AfxTermExtensionModule(ResouceDLL);

???????? return CWinApp::ExitInstance();

}

這樣我們就可以在應(yīng)用程序中安全的使用DLL中的資源了，就好比EXE中的一樣。對(duì)于我們自己編寫(xiě)入口函數(shù)的DLL，如果其中涉及到資源的話，我們可以參考上述的MFC常規(guī)DLL的實(shí)現(xiàn)。

對(duì)于我們?cè)贏ctiveX和一些DLL中的AFX_MANAGE_STATE(AfxGetStaticModuleState());我們又怎么理解呢？看看afxstat_.h：

#ifdef _AFXDLL

…

class _AFX_THREAD_STATE;

struct AFX_MAINTAIN_STATE2

{

???????? explicit AFX_MAINTAIN_STATE2(AFX_MODULE_STATE* pModuleState);

???????? ~AFX_MAINTAIN_STATE2();

protected:

???????? AFX_MODULE_STATE* m_pPrevModuleState;

???????? _AFX_THREAD_STATE* m_pThreadState;

};

#define AFX_MANAGE_STATE(p) AFX_MAINTAIN_STATE2 _ctlState(p);

#else? // _AFXDLL

#define AFX_MANAGE_STATE(p)

#endif //!_AFXDLL

?

對(duì)于在靜態(tài)庫(kù)中使用MFC　DLL時(shí)它就相當(dāng)于不存在，反之，它構(gòu)造一個(gè)AFX_MAINTAIN_STATE2對(duì)象,在afxstate.cpp中

#ifdef _AFXDLL

…

?

AFX_MAINTAIN_STATE2::AFX_MAINTAIN_STATE2(AFX_MODULE_STATE* pNewState)

{

???????? m_pThreadState = _afxThreadState;

???????? m_pPrevModuleState = m_pThreadState->m_pModuleState;

???????? m_pThreadState->m_pModuleState = pNewState;

}

#endif //_AFXDLL

,

再看dllmodul.cpp中有關(guān)AfxGetStaticModuleState的實(shí)現(xiàn)：

?

static _AFX_DLL_MODULE_STATE afxModuleState;

?

…

?

AFX_MODULE_STATE* AFXAPI AfxGetStaticModuleState()

{

???????? AFX_MODULE_STATE* pModuleState = &afxModuleState;

???????? return pModuleState;

}

?

(MFC中太多的全局變量的確不雅！)

可以看到通過(guò)構(gòu)造一個(gè)AFX_MAINTAIN_STATE2對(duì)象(再結(jié)合AfxGetResouceHandle的實(shí)現(xiàn))，就使AfxFindResourceHandle返回的是ActiveX控件（實(shí)際上也是一個(gè)常規(guī)DLL）或DLL的HINSTANE了，這樣AfxFindResourceHandle就不必須在DLL鏈表中查找了，但缺點(diǎn)是每次使用資源（或響應(yīng)消息）時(shí)都要構(gòu)造一個(gè)AFX_MAINTAIN_STATE2對(duì)象,并且，而且使用這種方法在此DLL中無(wú)法使用其它DLL中的資源或在EXE中使用DLL中的資源(在不使用AfxSetResourceHandle/AfxGetResourceHandle的前提下)。當(dāng)然，我們這兒關(guān)心的只是資源的使用，如果涉及到其它，包括事件響應(yīng)或多個(gè)UI線程時(shí)，AFX_MODULE_STATE還是不能少的。

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