Why a child window may not receive mouse events?

Question

I have a custom WTL control which is a panel with a list and a custom scroll bar.

class Panel
: public ATL::CWindowImpl<Panel>, public WTL::CDoubleBufferImpl<Panel> {
public:
    DECLARE_WND_CLASS("Panel")

    BEGIN_MSG_MAP_EX(Panel)
     MSG_WM_CREATE(OnCreate)
     MSG_WM_DESTROY(OnDestroy)
     MSG_WM_SIZE(OnSize)
     CHAIN_MSG_MAP(CDoubleBufferImpl<Panel>)
     REFLECT_NOTIFICATIONS()
    END_MSG_MAP()

The scroll bar is created by the panel in OnCreate():

m_scrollBar.Create(m_hWnd, WTL::CRect(...));

That scroll bar works fine in many other dialog windows. However, inside that panel control the scroll bar appears, but receives no mouse events at all. If I add WM_MOUSEMOVE handler to the panel, it does get called.

What could be the problem?

Answer 1

A good way to diagnose problems with Windows messaging is to use Spy++ or Winspector which allow you to get an under-the-covers look at Windows messaging.

Answer 2

Found it. The problem was in the scroll bar class declaration:

class CScrollBase : public ATL::CWindowImpl<CScrollBase, WTL::CStatic>

Changing to:

class CScrollBase : public ATL::CWindowImpl<CScrollBase>

makes the scroll bar work on the panel.