Creating a Modeless Dialog Box with MFC Libraries

ID: Q103788

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0

This article demonstrates how to create a modeless dialog box using a dialog-box template resource using MFC.

To build a CModeless dialog box, the following steps should be followed:

Create a dialog class derived from CDialog and override the Create() member function of CDialog. For example, you might have code that resembles the following:


      class CModeless: public CDialog
           {
             .
             .
             .
             public:
                 CModeless(){ }
                 BOOL Create(UINT nID, CWnd * pWnd)
                      { return CDialog::Create(nID,pWnd);}
             .
             .
             .
           };

NOTE: You could let ClassWizard generate the dialog class and then simply add the Create() function.

Write code to construct an object of the dialog class and create the dialog box window. For example, if you have a menu item that should display the dialog box, you might have code that resembles the following:
```
      void CMainFrame::OnModeless()
        {
            pdlg = new CModeless;
            pdlg->Create(IDD_DIALOG1,this);
        } 
```
where CMainFrame::pdlg is defined as:
CModeless * pdlg;
NOTE: It is important to allocate the object on the heap rather than the stack if you want to prevent the modeless dialog box from being destroyed when the function is exited.

You must call CWnd::DestroyWindow() in OnCancel, or whenever the modeless dialog box needs to be destroyed.
```
      void CModeless::OnCancel()
      {
          DestroyWindow();
      } 
```

Override CWnd::PostNcDestroy() in your dialog class to delete the dialog box object:
```
   virtual void CModeless::PostNcDestroy() {delete this;} 
```
PostNcDestroy() is a virtual member function of the CWnd class that is called by the OnNcDestroy() function.

A modeless dialog class will typically override the OnOK() and OnCancel() member functions to call DestroyWindow() and should not call the base class CDialog::OnOK() and CDialog::OnCancel() functions. The CDialog::OnOK() and CDialog::OnCancel() functions call EndDialog(). EndDialog() should be called only when using modal dialog boxes.

If you are using Dialog Data Exchange (DDX) and Dialog Data Validation (DDV), you're OnOK() handler for your dialog class might resemble the following:


   void CModeless::OnOK()
   {
           if (!UpdateData(TRUE))
             {
               TRACE0("UpdateData failed during dialog termination\n");
               // The UpdateData routine will set focus to correct item
               return;
             }
           DestroyWindow();
   }

Additional query words: kbinf 1.00 1.50 2.00 2.10 2.50 2.51 2.52 3.00 3.10 4.00


Keywords          : kbMFC KbUIDesign kbVC 
Version           : WINDOWS:1.00,1.50,1.51,1.52; winnt:1.00,2.00
Platform          : WINDOWS winnt 
Issue type        : kbhowto

Last Reviewed: July 27, 1999