FIX: Icons, Bitmaps, & Menus Not Displayed in an AFXDLL Dialog

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit edition, version 4.0

SYMPTOMS

Additional resources specified in a dialog template of a dialog implemented in an extension DLL will be displayed incorrectly or not displayed at all. That can affect icons, bitmaps, and menus that are specified in a dialog template.

CAUSE

The implementation of the CDialog class was changed in MFC version 4.0. The previous implementation of CDialog used a ::DialogBox() call to create a modal dialog and passed an instance handle obtained from a call to AfxFindResourceHandle() as a handle of the module where resources were stored. It was possible to call AfxSetResourceHandle() or use an extension DLL to find a dialog template that was stored in another module.

The new implementation first loads dialog template. Then it calls ::CreateDialogIndirect(), passing a handle obtained from a call to AfxGetInstanceHandle(). This handle is the handle of the executable module; it is not the handle of the one that contains additional resources. Therefore, no additional resources will be found or displayed.

Note that it is also possible that you have another resource in the executable module with the same ID as the one required for the dialog. This would cause an incorrect resource to be displayed.

This is a problem when you have a dialog template located in an extension DLL, or a resource only DLL. This is not a problem for regular DLLs.

RESOLUTION

To correct this problem, you have to set the current handle to be the one that corresponds to the module containing a dialog template. You also need to reset the handle back to the old value before proceeding with any code that involves the dialog. The easiest way to achieve this is to override DoModal in your CDialog derived class as in this example:

int CMyDialog::DoModal()

    m_hInstSave = afxCurrentInstanceHandle;
    afxCurrentInstanceHandle = AfxFindResourceHandle(
        MAKEINTRESOURCE(IDD), RT_DIALOG);

    return CDialog::DoModal();

Here m_hInstSave is a data member of CMyDialog of type HINSTANCE. The variable afxCurrentInstanceHandle is used by MFC to store the current instance handle. Its value is returned from AfxGetInstanceHandle(), and it is defined in Afxwin.h.

This implementation sets the current instance handle to the one that is returned from AfxFindResourceHandle(), which searches through the list of available extension DLLs for a dialog template. If you are using a resource only DLL, you will probably use AfxSetResourceHandle() to set the MFC current resource handle to the one that corresponds to the DLL. In that case, you can set afxCurrentInstanceHandle either directly using the same value or with a value returned from AfxGetResourceHandle().

To reset the current instance handle back to the saved value, you need to have a handler for the WM_INITDIALOG message, OnInitDialog, with the following code:

BOOL CMyDialog::OnInitDialog() {

    afxCurrentInstanceHandle=m_hInstSave;

    CDialog::OnInitDialog();

    // some other code...

    return TRUE;

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in Visual C++, 32-bit Edition, version 4.1.

REFERENCES

For the implementation of the CDialog class, refer to the Dlgcore.cpp file, located in MFC source code directory, \Msdev\Mfc\Src.