Bob Moore's Coding Tips

26. How do I make an invisible dialog-based application?

MFC dialog-based apps default to using a modal dialog, which causes problems if your application requires to be invisible. This situation most commonly occurs when developing applications which place icons in the system tray, and therefore need their main dialog to be invisible until the user interacts with the icon. You can make a modeless dialog version of your app as follows:

smallbluething.gif (904 bytes) Make your dialog resource invisible using the styles tab in the dialog properties.
smallbluething.gif (904 bytes) Remove all the DoModal gunk from your InitInstance, so you end up with something like this :

BOOL CMyApp::InitInstance()
{
   #ifdef _AFXDLL
    Enable3dControls(); // using MFC in a shared DLL
   #else
    Enable3dControlsStatic();    // linking to MFC statically
   #endif

   m_pMainWnd = new CMyModelessDlg;

   if (m_pMainWnd)
      return TRUE;
   else
      return FALSE;
}
smallbluething.gif (904 bytes) I place the call to Create (...) in my dialog constructor and make it public. Other people organise things differently but it works for me... curse the OOP thought police <g> :

CMyModelessDlg::CMyModelessDlg(CWnd* pParent /*=NULL*/)
    : CDialog(CMyModelessDlg::IDD, pParent)
{
   //{{AFX_DATA_INIT(CMyModelessDlg)
   //}}AFX_DATA_INIT
   m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);

   Create (IDD, pParent); // Create modeless dialog.
}
smallbluething.gif (904 bytes) You will need to handle PostNcDestroy and delete the dialog object yourself (ClassWizard can set up the handler for you) :

void CMyModelessDlg::PostNcDestroy()
{
   delete this;
}
smallbluething.gif (904 bytes) You may find that if you call DestroyWindow from within your dialog in order to shut down, you will have to call your own PostNcDestroy in order to avoid a leak. Watch the debug output from your app running in debug mode - if this is the case MFC will helpfully give you a warning there. Here's the normal WM_CLOSE handler:

void CMyModelessDlg::OnClose() 
{
   if (m_bOkToClose)
   {
      CleanUp ();
      DestroyWindow ();
   }
   else
   {
      ShowWindow (SW_HIDE);
   }
}

I use the m_bOkToClose flag to distinguish when I'm permitting the user to close down and when I want that action to simply hide the window. Cleanup is a function that does any necessary CloseHandles, removes any tray icons and deletes any allocated memory.

Now you have a dialog based application that can be shown or hidden as necessary.