windows编程中为滚动条写了按键的代码，但是按了相应的键不起作用。

Question

代码如下：
case WM_KEYDOWN:
switch (message)
{
case VK_HOME:
SendMessage(hwnd, SB_VERT, SB_TOP, 0L);
case VK_END:
SendMessage(hwnd, SB_VERT, SB_BOTTOM, 0L);
break;
case VK_PRIOR:
SendMessage(hwnd, SB_VERT, SB_PAGEUP, 0L);
break;
case VK_NEXT:
SendMessage(hwnd, SB_VERT, SB_PAGEDOWN, 0L);
break;
case VK_UP:
SendMessage(hwnd, SB_VERT, SB_LINEUP, 0L);
break;
case VK_DOWN:
SendMessage(hwnd, SB_VERT, SB_LINEDOWN, 0L);
break;
case VK_LEFT:
SendMessage(hwnd, SB_HORZ, SB_PAGEDOWN, 0L);
break;
case VK_RIGHT:
SendMessage(hwnd, SB_HORZ, SB_PAGEUP, 0L);
break;
default:
break;
}
return 0;