Microsoft KB Archive/114376

= FIX: CWnd::ExecuteDlgInit Uses AfxGetInstanceHandle =

Article ID: 114376

Article Last Modified on 11/21/2006

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APPLIES TO

 Microsoft Foundation Class Library 4.2, when used with:  Microsoft Visual C++ 1.0 Professional Edition

 Microsoft Visual C++ 1.0 Professional Edition 

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This article was previously published under Q114376



SYMPTOMS
In the Microsoft Foundation Classes, version 2.0, CWnd::ExecuteDlgInit incorrectly searches for dialog box resources only in the executing module.



CAUSE
In WINCORE.CPP, lines 1463 and 1464, CWnd::ExecuteDlgInit attempts to find the specified resource using the following code: if ((hDlgInit = ::FindResource(AfxGetInstanceHandle,       lpszResourceName, RT_DLGINIT)) != NULL) This forces the use of only those resources bound to the executing module. For localization and other uses, it must be possible to load resources from other sources.



RESOLUTION
This problem was fixed in the Microsoft Foundation Classes, version 2.5, which is supplied with Visual C++ for Windows, version 1.5. The fix involves defining AfxFindResourceHandle to return the correct resource handle either by using AfxGetResourceHandle for a single executable or by searching the list of CDynLinkLibrary objects for an application using the shared dynamic link library (DLL) version of the Microsoft Foundation Class library (compiling using _AFXDLL). This allows the application to switch between several sets of resources located in DLLs.

Applications maintain a list of the shared and extension DLLs using instances of the CDynLinkLibrary class. Each node in the list is an object of the CDynLinkLibrary class or of a class derived from the CDynLinkLibrary class. This object can also be used to hold private data for the DLL by deriving from CDynLinkLibrary and adding additional member variables. For an example of CDynLinkLibrary, please examine the Microsoft Foundation Class library DLLHUSK sample supplied with Visual C++, versions 1.0 and 1.5.

In a Microsoft Foundation Class application that does not use the shared DLL (MFC2xx.DLL), AfxFindResourceHandle calls AfxGetResourceHandle, which returns the current resource handle for the executable. In a Microsoft Foundation Class application that uses MFC2xx.DLL, AfxFindResourceHandle traverses the CDynLinkLibrary object list of shared and extension DLLs, looking for the correct resource handle.

To get this behavior in a Microsoft Foundation Class library version 2.0 application, add the following function to the source module that contains the dialog box class code: HINSTANCE ResourceInit(LPCSTR szResourceName,LPCSTR szResType) {   // first check the app HINSTANCE hInstApp = AfxGetResourceHandle; if (::FindResource(hInstApp, szResourceName, szResType) != NULL) return hInstApp;

// check for DLLs in proper order CDynLinkLibrary* pDLL; for (pDLL = _AfxGetAppData->pFirstDLL; pDLL != NULL;        pDLL = pDLL->m_pNextDLL) {       if (pDLL->m_hResource != NULL &&            ::FindResource(pDLL->m_hResource, szResourceName, szResType) != NULL) {           // found it in a DLL, use it's resource handle return pDLL->m_hResource; }   }

// if failed to find resource, fail initialization TRACE("\n Resource not found \n"); return (HINSTANCE)NULL; } Make a call to this function in the CDialog derived class' override of OnInitDialog. The ResourceInit function will check the list of CDynLinkLibrary objects for the application and return the appropriate resource handle (or NULL if not found). The OnInitDialog function may look like this: BOOL CDerivedDlg::OnInitDialog {   // attempt to find dialog box template HINSTANCE hResInst = ResourceInit(m_lpDialogTemplate, RT_DIALOG); if(NULL == hResInst) return FALSE;

// get app's resource handle so we can set it back later HINSTANCE hAppInst = AfxGetResourceHandle; // temporarily set to DLL's resource handle AfxSetResourceHandle(hResInst); // Call base class which initializes the dialog // and loads the template BOOL bInit = CDialog::OnInitDialog; // restore the app's resource handle AfxSetResourceHandle(hAppInst);

return bInit; } In addition, the resource handle must be set correctly before the call to DoModal. The easiest way to do this is to:


 * 1) Call ResourceInit from the constructor of the dialog box.
 * 2) Set the resource handle for the application appropriately.
 * 3) Reset it to the actual application resource handle when the dialog box is destroyed.

Here is an example of the constructor: CDerivedDlg::CDerivedDlg(CWnd* pParent /*=NULL*/) : CDialog(CDerivedDlg::IDD, pParent) {   //AFX_DATA_INIT AfxSetResourceHandle(ResourceInit(m_lpDialogTemplate,RT_DIALOG)); } Here is an example of the destructor: CDerivedDlg::~CDerivedDlg {   AfxSetResourceHandle(AfxGetApp->m_hInstance); // reset resource to application's instance handle } The ResourceInit function may be used at any point for any type of resource that may be located in a DLL or in the application's resources.

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STATUS
Microsoft has confirmed this to be a problem in the Microsoft Foundation Classes, version 2.0. The problem was corrected in Microsoft Foundation Classes, version 2.5.

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