In the Microsoft Foundation Classes, version 2.0, CWnd::ExecuteDlgInit()
incorrectly searches for dialog box resources only in the executing
module.
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.
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:
- Call ResourceInit() from the constructor of the dialog box.
- Set the resource handle for the application appropriately.
- 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(CDerivedDlg)
// NOTE: the ClassWizard will add member initialization here
//}}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.
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.