To start an application minimized (e.g. appearing directly in the tray area), the common way to do this is calling ShowWindow(SW_HIDE) as soon as possible, preferably directly after the call to CDialog::OnInitDialog().

This surely does the trick, but every now and then, you will see your main dialog window flickering for a fraction of a second before it is finally hidden or sent to the tray area.

This is because the basic window has already been created when CDialog::OnInitDialog() returns, and its default behaviour is to appear on screen (in fact, this is what windows were made for).

Maybe in a few years, when computers operate much more faster than they do now, you’ll get rid of this annoying flickering automatically, because your Operating System will then hide your window before you even start the corresponding application.

But for now, just add this OnWindowPosChanging() handler to your application:

void CTestDlg::OnWindowPosChanging(WINDOWPOS* lpwndpos) 
{
    if(m_bDlgVisible == false)
        lpwndpos->flags &= ~SWP_SHOWWINDOW;
 
    CDialog::OnWindowPosChanging(lpwndpos);
}

You can also declare an optional boolean member variable (m_bDlgVisible in this example), which is initialized to true in the constructor and gets toggled in the corresponding SendToTray() and RestoreFromTray() functions. This way, I can track the current window state (IsWindowVisible() would also work) for different purposes.