WTL 给一个对话框添加垂直滚动条

MESSAGE_HANDLER(WM_VSCROLL, OnVscroll)
MESSAGE_HANDLER(WM_SIZE, OnSize)
MESSAGE_HANDLER(WM_MOUSEWHEEL, OnMouseWheel)

::GetWindowRect(m_hWnd, &m_wndRect);
ScreenToClient(&m_wndRect);
m_nScrollPos = 0;

LRESULT OnVscroll(UINT /*uMsg*/, WPARAM wParam, LPARAM /*lParam*/, BOOL& /*bHandled*/)
{
int curPos = HIWORD(wParam);
int nDelta = 0;
int nScrollStep = (m_nScrollRange) / 9;
m_nScrollPos = ::GetScrollPos(m_hWnd, SB_VERT);
switch (LOWORD(wParam))
{
case SB_LINEDOWN:
if (m_nScrollPos >= m_nScrollRange)
{
return 0;
}
nDelta = min(nScrollStep, m_nScrollRange - m_nScrollPos);
break;
case SB_LINEUP:
if (m_nScrollPos <= 0)
{
return 0;
}
nDelta = -min(nScrollStep, m_nScrollPos);
break;
case SB_PAGEDOWN:
if (m_nScrollPos >= m_nScrollRange)
{
return 0;
}
nDelta = min(m_nScrollRange, m_nScrollRange - m_nScrollPos);
break;
case SB_PAGEUP:
if (m_nScrollPos <= 0)
{
return 0;
}
nDelta = -min(m_nScrollRange, m_nScrollPos);
break;
case SB_THUMBPOSITION:
case SB_THUMBTRACK:
nDelta = curPos - m_nScrollPos;
break;
default:
break;
}
m_nScrollPos += nDelta;
::SetScrollPos(m_hWnd, SB_VERT, m_nScrollPos, TRUE);
::ScrollWindow(m_hWnd, 0, -nDelta, NULL, m_wndRect);
::UpdateWindow(m_hWnd);
return 0;
}
LRESULT OnSize(UINT /*uMsg*/, WPARAM wParam, LPARAM lParam, BOOL& /*bHandled*/)
{
SCROLLINFO si;
si.cbSize		= sizeof(SCROLLINFO);
si.fMask		= SIF_ALL;
si.nMin			= 0;
si.nMax			= m_wndRect.Height();			//窗口的实际高度
si.nPage		= HIWORD(lParam);				//窗口的显示高度
si.nPos			= 0;
SetScrollInfo(SB_VERT, &si, TRUE);

m_nScrollRange = si.nMax - si.nPage;			//滚动范围
return 0;
}
LRESULT OnMouseWheel(UINT , WPARAM wParam, LPARAM , BOOL& )
{
MouseWheelHandle(HIWORD(wParam));
return 0;
}
void MouseWheelHandle(short nDir)
{
if (nDir > 0)
{
::SendMessage(m_hWnd, WM_VSCROLL, SB_LINEUP, 0);
}
else if (nDir < 0)
{
::SendMessage(m_hWnd, WM_VSCROLL, SB_LINEDOWN, 0);
}
}