How to Create a Modal Dialog from Within a USRDLL

WINDOWS   | WINDOWS NT

The information in this article applies to:

• The Microsoft Foundation Classes (MFC), included with:

      - Microsoft Visual C++ for Windows, versions 1.5 and 1.51
      - Microsoft Visual C++, 32-bit Edition, version 2.0 and 4.0
  

SUMMARY

When creating a modal dialog box from within a USRDLL, or a regular DLL statically linked to the MFC, you need to pass a valid parent window object to the CDialog constructor. You cannot pass the CWnd pointer from an EXE to an USRDLL, so you need to pass the HWND of the parent window.

You can use two methods to construct the CDialog object with the HWND as its parent. You can either construct a CWnd object and use the Attach() function to attach the HWND to it, or you can use CWnd::FromHandle. After that you can use the CWnd object as the parent of the CDialog object.

The DLLTRACE sample program demonstrates the latter method and demonstrates how to delete the temporary objects created by MFC in the OnIdle() handler.

To construct a modal dialog in the USRDLL, export a "C" interface function that takes an HWND as a parameter:

   export "C"
   {
      void FAR PASCAL _export CreateModal(HWND hParent);
   }

MORE INFORMATION

Modal dialog requires a valid parent window to be modal. If the parent window is invalid or NULL, the dialog will not be modal and it will not prevent the user from switching to the other windows of the application.

Sample Code

/* Compile options needed: standard USRDLL options
*/

void FAR PASCAL _export CreateModal(HWND hParent)

    TRACE("Inside USRDLL\n");

    CWnd wndParent;

    if (!wndParent.Attach(hParent) )
    {
        TRACE("Attach Failed\n");
        AfxAbort();
    }

    CMyDialog Dlg(IDD_DIALOG1, &wndParent);    // IDD_DIALOG1 is in
                                               // the DLL resource
    if ( Dlg.DoModal() == IDOK )
    {
        // more code
    }
    else
    {
        // check for cancel or error
    }
    wndParent.Detach(hwndParent);

Note: In Visual C++ version 4.0, the term "USRDLL" is obsolete. In

   earlier versions, USRDLL described DLLs that used MFC internally,
   but typically export functions using the standard "C" interface.
   In version 4.0, such DLLs are called "Regular DLLs." Regular DLLs,
   statically linked to MFC have the same characteristics as the
   former USRDLL.