近来在论坛上很有多帖子问到如何使用DLL中的资源(包括对话框，图标等)的问题，现在笔者就来就此问题谈谈，包含在DLL内部使用资源，DLL中使用其它DLL中的资源和在应用程序中使用资源。

我们先以图标为例说起(其它的资源与此图标的加载原理大致相同)，我们要加载图标，一般是调用AfxGetApp()->LoadIcon(…)；下面是CWinApp::LoadIcon的实现(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实际上调用了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是我们要加载ICON的模块实例，这个实例从何来，当然我们可以直接传入DLL的实例，对于通过LoadLibrary动态加载的DLL我们可以很容易的得到其句柄，但对于我们直接链接的DLL得到其句柄则要费一番周折。可以看到CWinApp::LoadIcon是通过AfxFindResouceHandle找到此句柄的。下面是AfxFindResourceHandle的定义(afxwin.h)：

#ifndef _AFXDLL

#define AfxFindResourceHandle(lpszResource, lpszType) AfxGetResourceHandle()

#else

HINSTANCE AFXAPI AfxFindResourceHandle(LPCTSTR lpszName, LPCTSTR lpszType);

#endif

我们先讨论在静态链接库中使用MFC　DLL的情况。可以看到，我们如果在静态库中使用MFC　DLL的话(#ifndef _AFXDLL),实际上就是调用的AfxGetResourceHandle，MSDN中的说明是

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.

函数返回的应用程序加载的缺省资源的HINSTANCE句柄,HINSTANCE相当于HMODULE，也就是资源所在的模块句柄。显然在此，我们使用的是DLL中的资源，那么我们就应该返回此DLL中的HINSTANCE了，如果让AfxGetResourceHandle返回DLL的HINSTANCE呢？答案是通过AfxSetResourceHandle设置。MSDN中AfxSetResouceHandle的说明如下：

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.

我们只需将DLL的HINSTANCE传入AfxSetResouceHanle就行了。如何得到DLL的HINSTANCE呢，我们可以通过DLL声明一个接口HINSTANCE GetInstance获得，也可以通过EnumProcessMoudules找到（详细的过程见MSDN中EnumProcessModules的说明和示例）。

我们使用完DLL中的资源要使用EXE中的资源的资源怎么办呢？我们需要在使用完成后用AfxSetResource重新将资源模块的句柄设置为原来的值，如果来保证在资源使用完成后完成这一个工作呢，即使在使用过程中发生异常了，为此我们利C++类的构造和析构机制创建了这一类：

class CLocalResource

{

public:

CLocalResource(HINSTANCE hInstance)

{

m_hInstOld=AfxGetInstanceHandle();

AfxSetInstanceHandle(hInstance);

}

virtual ~CLocalResource()

{

AfxSetInstanceHandle(m_hInstOld);

}

protected:

HINSTANCE m_hInstOld;

};

我们只需在使用DLL的资源之前构造一个CLocalInstance就行了。

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

{

CLocalResouce localRes(hInst);

…

}

下面来讨论在动态库中使用MFC DLL的情况(也就是定义了_AFXDLL的情况)

来看看AfxGetInstanceHandle ,AfxGetResourceHandle和AfxSetResouceHandle的实现(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; }

实际上访问的就是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在此我们就不讨论了，有兴趣的读者可以阅读(afxstat_.h和afxstate.cpp)。

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

我们可以在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调用的，那AfxWinInit又由谁调用呢？

我们可以在DllMain(dllinit.cpp和dllmodul.cpp，分别对应于MFC扩展DLL和MFC规则DLL)看到

(dllinit.cpp,MFC扩展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);

….

}

…

}

可以看到在提供自动化支持时，将调用AfxWinInit(但MFC的DLL向导，对于扩展DLL却不允许添加自动化支持)。

(在dllmodul.cpp中，MFC常规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

}

…

}

看到上面的代码，其实与MFC扩展DLL的代码大同小异，只过是MFC常规DLL可以支持在静态链接库全用MFC DLL，相应的初始化/反初始化函数就变为了AfxInitLocalData/ AfxTermLocalData,在此我们不对在静态链接库中使用MFC DLL的情况作更多讨论。

以及在winmain.cpp中的int AFXAPI AfxWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,LPTSTR lpCmdLine, int nCmdShow),在appmodul.cpp中我们可以看到入口函数的实现：

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的定义(afxdll_.h)和实现(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);

}

由此我们可以看出DLL初始化时先调AfxInitExtensionModule是为了构造一个AFX_EXTENSION_MODULE,然后将它插入插入一个AFX_MODULE_STATE链表中,同时将当前DLL的HINSTANCE插入此AFX_MODULE_STATE的CDynLinkLibrary链表中，以便稍后讲到的AfxFindResourceHandle找到。DLL从内存移出时就从此链表中删除自己。

让我们来看看AfxFindResourceHandle的实现(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();

}

上面的代码首先检查主模块的状态,通过返回的是个AFX_MODULE_STATE的类对象指针. AFX_MODULE_STATE又是个什么呢？下面看看AFX_MODULE_STATE的定义(afxstat_.h中,它的实现在afxstate.cpp中，有兴趣的读者可以读读)：

// 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

….

};

我们来看看我们关心的属性

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;

看了相关注释，也就明白什么意思了，在此就不多解释了。

如果当前主模块是系统模块(通过m_bSystem标识)，并且从当前模块中找到了相应的资源就返回此模块的HINSTANCE。接下来当前模块所载的DLL链表中的所有用户模块中查找，本地化的MFC资源DLL中查找，系统DLL中查找。如果都找不到则从EXE(或者通过AfxSetResouceHandle中设置的HINSTANCE)中查找。

如果不考虑DLL链表，则需要我们每次使用DLL中的资源前调用AfxSetResouceHandle，使用后再调用AfxSetResourceHandle，就同前面讲的在静态链接库中使用MFC　DLL一样。麻不麻烦？

怎么解决呢？解决方法是用资源DLL的HINSTANCE构造一CDynLinkLibrary对象插入主模块(EXE)的AFX_MODULE_STATE的m_libraryList中。怎么做？

看了上面DllMain的实现代码，我们可以照着做。

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();

}

这样我们就可以在应用程序中安全的使用DLL中的资源了，就好比EXE中的一样。对于我们自己编写入口函数的DLL，如果其中涉及到资源的话，我们可以参考上述的MFC常规DLL的实现。

对于我们在ActiveX和一些DLL中的AFX_MANAGE_STATE(AfxGetStaticModuleState());我们又怎么理解呢？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

对于在静态库中使用MFC　DLL时它就相当于不存在，反之，它构造一个AFX_MAINTAIN_STATE2对象,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中有关AfxGetStaticModuleState的实现：

static _AFX_DLL_MODULE_STATE afxModuleState;

…

AFX_MODULE_STATE* AFXAPI AfxGetStaticModuleState()

{

AFX_MODULE_STATE* pModuleState = &afxModuleState;

return pModuleState;

}

(MFC中太多的全局变量的确不雅！)

可以看到通过构造一个AFX_MAINTAIN_STATE2对象(再结合AfxGetResouceHandle的实现)，就使AfxFindResourceHandle返回的是ActiveX控件（实际上也是一个常规DLL）或DLL的HINSTANE了，这样AfxFindResourceHandle就不必须在DLL链表中查找了，但缺点是每次使用资源（或响应消息）时都要构造一个AFX_MAINTAIN_STATE2对象,并且，而且使用这种方法在此DLL中无法使用其它DLL中的资源或在EXE中使用DLL中的资源(在不使用AfxSetResourceHandle/AfxGetResourceHandle的前提下)。当然，我们这儿关心的只是资源的使用，如果涉及到其它，包括事件响应或多个UI线程时，AFX_MODULE_STATE还是不能少的。