FIX: SetWindowText(NULL) Doesn't Clear .OCX Edit Control

SYMPTOMS

It is possible to use AppWizard to create an OLE Custom Control (.ocx file) that subclasses a standard Windows control. If you choose to subclass an edit control, the control will not exhibit the same behavior as a standard edit control.

Specifically, in the case where the control is not initialized with data, the user types some text into the control, and then SetWindowText(NULL) is called to clear the text, the text in the control will not be cleared. If this same sequence of events were to occur in a standard edit control, the contents of the edit control would be cleared.

LRESULT COleControl::OnSetText(WPARAM wParam, LPARAM lParam)
{
   ASSERT(lParam == 0 || AfxIsValidString((LPCTSTR)lParam));
   // Is the property changing?
   if ((lParam == 0 && m_strText.IsEmpty()) ||
      (lParam != 0 && m_strText == (LPCTSTR)lParam))
      return 0;
           .
         .
         .
}
				

LRESULT CMyOleControl::OnSetText(WPARAM wParam, LPARAM lParam)
{
   ASSERT(lParam == 0 || AfxIsValidString((LPCTSTR)lParam));
   // Is the property changing?
   if ((lParam == 0 && InternalGetText().IsEmpty()) ||
      (lParam != 0 && m_strText == (LPCTSTR)lParam))
      return 0;
                    .
         .
         .
}