Using a modal or modeless dialog as a main window

29 Jan 2004 20:37 mfc

Using a modal dialog as a main window

If you ask the MFC AppWizard to generate a dialog-based application, it generates code that looks like this:

BOOL CModalApp::InitInstance()
{
    CModalDlg dlg;
    m_pMainWnd = &dlg;
    int nResponse = dlg.DoModal();

    // TODO: Do something, based on nResponse (IDOK or IDCANCEL)

    // Since the dialog has been closed, return FALSE so that we exit the
    //  application, rather than start the application's message pump.
    return FALSE;
}

Using a modeless dialog as a main window

Unfortunately, this doesn’t work properly if you have control bars in your dialog. This is because DoModal doesn’t use the standard MFC message loop. This means that OnIdle is not called. If OnIdle is not called, then WM_IDLEUPDATECMDUI is not sent, and the control bars aren’t updated correctly.

We solve this by using a modeless dialog as our main window:

BOOL CCustomDrawApp::InitInstance()
{
    CModelessDialog *dlg = new CModelessDialog;
    if (!dlg->Create())
	    return FALSE;

    m_pMainWnd = dlg;
    return TRUE;
}

BOOL CModelessDialog::Create(CWnd* pParent /*=NULL*/)
{
    return CDialog::Create(CModelessDialog::IDD, pParent);
}

To get this to work (otherwise the application doesn’t exit when you press the OK or Cancel buttons), you’ll also need to handle OnOK and OnCancel:

void CModelessDialog::OnOK()
{
    CDialog::OnOK();

    DestroyWindow();
}

void CModelessDialog::OnCancel()
{
    CDialog::OnOK();

    DestroyWindow();
}

And to fix the memory leak, handle PostNcDestroy:

void CModelessDialog::PostNcDestroy()
{
    CDialog::PostNcDestroy();

    delete this;
}