C / C++ / MFC

static const UINT UDM_START_PROCESSING = ::RegisterWindowMessage(_T("UDM_START_PROCESSING"));
 
BEGIN_MESSAGE_MAP(CMyDialog, CDialog)
    //{{AFX_MSG_MAP(CMyDialog)
    //}}AFX_MSG_MAP
    ON_REGISTERED_MESSAGE(UDM_START_PROCESSING, OnStartProcessing)
END_MESSAGE_MAP()
 
BOOL CMyDialog::OnInitDialog( void )
{
    CDialog::OnInitDialog();
 
    PostMessage(UDM_START_PROCESSING);
 
    return TRUE;
}
 
LRESULT CMyDialog::OnStartProcessing( WPARAM, LPARAM )
{
    return (0);
}

...
CDialog::OnInitDialog();
SendMessageToDescendants(WM_SHOWWINDOW, (WPARAM)TRUE);
SendMessageToDescendants(WM_ENABLE , (WPARAM)TRUE);
OnUpdate();
return TRUE;

BOOL CDlgXXX::OnInitDialog() 
{
    CDialog::OnInitDialog();
    // Init stuff that needs to be initialized here 
    SetTimer(TIMER_ID, 50, NULL)
    return TRUE;  
}

void CDlgXXX::OnTimer(UINT nIDEvent) 
{
    if (TIMER_ID == nIDEvent)
    {
        KillTimer(TIMER_ID);
        // Do stuff that needs to be done when gui is visible
        return;
    }
    CDialog::OnTimer(nIDEvent);
}