Q121947: How to Create a Modal Dialog from Within a USRDLL

Article: Q121947
Product(s): Microsoft C Compiler
Version(s): 1.50 1.51 | 2.00 4.00
Operating System(s): 
Keyword(s): kbcode
Last Modified: 29-JUL-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), included with:
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.5, 1.51 
   - Microsoft Visual C++, 32-bit Editions, versions 2.0, 4.0 
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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);
     }


The implementation of the CreateModal() is below.

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Note: In Visual C++ version 4.0, the term "USRDLL" is obsolete.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

Additional query words: kbinf modal dialog CDialog DLL USRDLL 1.50 2.00 2.50 2.51 3.00 4.00

======================================================================
Keywords          : kbcode 
Technology        : kbAudDeveloper kbMFC
Version           : 1.50 1.51 | 2.00 4.00

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