如何使用动态链接库中的资源
近來在論壇上很有多帖子問到如何使用DLL中的資源(包括對話框，圖標等)的問題，現在筆者就來就此問題談談，包含在DLL內部使用資源，DLL中使用其它DLL中的資源和在應用程序中使用資源。
?????? 我們先以圖標為例說起(其它的資源與此圖標的加載原理大致相同)，我們要加載圖標，一般是調用AfxGetApp()->LoadIcon(…)；下面是CWinApp::LoadIcon的實現(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實際上調用了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的模塊實例，這個實例從何來，當然我們可以直接傳入DLL的實例，對于通過LoadLibrary動態加載的DLL我們可以很容易的得到其句柄，但對于我們直接鏈接的DLL得到其句柄則要費一番周折?？梢钥吹紺WinApp::LoadIcon是通過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
?????? 我們先討論在靜態鏈接庫中使用MFC DLL的情況。可以看到，我們如果在靜態庫中使用MFC DLL的話(#ifndef _AFXDLL),實際上就是調用的AfxGetResourceHandle，MSDN中的說明是
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.
函數返回的應用程序加載的缺省資源的HINSTANCE句柄,HINSTANCE相當于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，那么我們就應該返回此DLL中的HINSTANCE了，如果讓AfxGetResourceHandle返回DLL的HINSTANCE呢？答案是通過AfxSetResourceHandle設置。MSDN中AfxSetResouceHandle的說明如下：
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DLL聲明一個接口HINSTANCE GetInstance獲得，也可以通過EnumProcessMoudules找到（詳細的過程見MSDN中EnumProcessModules的說明和示例）。
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置為原來的值，如果來保證在資源使用完成后完成這一個工作呢，即使在使用過程中發生異常了，為此我們利C++類的構造和析構機制創建了這一類：
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的資源之前構造一個CLocalInstance就行了。
void CXXXX::LoadResouceFromDLL(HINSTANCE hInst,UINT nResID,…)
{
???????? CLocalResouce localRes(hInst);
???????? …
}
下面來討論在動態庫中使用MFC DLL的情況(也就是定義了_AFXDLL的情況)
來看看AfxGetInstanceHandle ,AfxGetResourceHandle和AfxSetResouceHandle的實現(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; }
實際上訪問的就是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調用的，那AfxWinInit又由誰調用呢？
我們可以在DllMain(dllinit.cpp和dllmodul.cpp，分別對應于MFC擴展DLL和MFC規則DLL)看到
(dllinit.cpp,MFC擴展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化支持時，將調用AfxWinInit(但MFC的DLL向導，對于擴展DLL卻不允許添加自動化支持)。
(在dllmodul.cpp中，MFC常規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，其實與MFC擴展DLL的代碼大同小異，只過是MFC常規DLL可以支持在靜態鏈接庫全用MFC DLL，相應的初始化/反初始化函數就變為了AfxInitLocalData/ AfxTermLocalData,在此我們不對在靜態鏈接庫中使用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的實現：
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)和實現(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初始化時先調AfxInitExtensionModule是為了構造一個AFX_EXTENSION_MODULE,然后將它插入插入一個AFX_MODULE_STATE鏈表中,同時將當前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從內存移出時就從此鏈表中刪除自己。
讓我們來看看AfxFindResourceHandle的實現(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,通過返回的是個AFX_MODULE_STATE的類對象指針. AFX_MODULE_STATE又是個什么呢？下面看看AFX_MODULE_STATE的定義(afxstat_.h中,它的實現在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
….
};
我們來看看我們關心的屬性
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;
看了相關注釋，也就明白什么意思了，在此就不多解釋了。
?
如果當前主模塊是系統模塊(通過m_bSystem標識)，并且從當前模塊中找到了相應的資源就返回此模塊的HINSTANCE。接下來當前模塊所載的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DLL中查找。如果都找不到則從EXE(或者通過AfxSetResouceHandle中設置的HINSTANCE)中查找。
如果不考慮DLL鏈表，則需要我們每次使用DLL中的資源前調用AfxSetResouceHandle，使用后再調用AfxSetResourceHandle，就同前面講的在靜態鏈接庫中使用MFC DLL一樣。麻不麻煩？
怎么解決呢？解決方法是用資源DLL的HINSTANCE構造一CDynLinkLibrary對象插入主模塊(EXE)的AFX_MODULE_STATE的m_libraryList中。怎么做？
看了上面DllMain的實現代碼，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用程序中安全的使用DLL中的資源了，就好比EXE中的一樣。對于我們自己編寫入口函數的DLL，如果其中涉及到資源的話，我們可以參考上述的MFC常規DLL的實現。
對于我們在ActiveX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
?
對于在靜態庫中使用MFC DLL時它就相當于不存在，反之，它構造一個AFX_MAINTAIN_STATE2對象,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AfxGetStaticModuleState的實現：
?
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！)
可以看到通過構造一個AFX_MAINTAIN_STATE2對象(再結合AfxGetResouceHandle的實現)，就使AfxFindResourceHandle返回的是ActiveX控件（實際上也是一個常規DLL）或DLL的HINSTANE了，這樣AfxFindResourceHandle就不必須在DLL鏈表中查找了，但缺點是每次使用資源（或響應消息）時都要構造一個AFX_MAINTAIN_STATE2對象,并且，而且使用這種方法在此DLL中無法使用其它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)。當然，我們這兒關心的只是資源的使用，如果涉及到其它，包括事件響應或多個UI線程時，AFX_MODULE_STATE還是不能少的。
超強干貨來襲 云風專訪：近40年碼齡，通宵達旦的技術人生總結
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