How to Create a Modal Dialog from Within a USRDLL

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.

\* kbon
/* 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);
}
\* kboff