TrackPopupMenuEx没有在CWinThread中看到键

Question

我在UI CWinThread中使用TrackPopupMenuEx， CMonitor源自CWinThread

    monitor_ = (CMonitor *)AfxBeginThread(RUNTIME_CLASS(CMonitor));

CMonitor :: InitInstance包含

m_pMainWnd = new CWnd();
m_pMainWnd->CreateEx(WS_EX_TOOLWINDOW | WS_EX_CONTROLPARENT | WS_EX_WINDOWEDGE | WS_EX_TOPMOST, AfxRegisterWndClass(CS_DBLCLKS),
    NULL, WS_POPUP | WS_CLIPSIBLINGS | WS_VISIBLE, 50, 50, 50, 50, NULL, NULL);

然后我做

    SetForegroundWindow(AfxGetMainWnd()->m_hWnd);

auto popup_menu_flags = TPM_RETURNCMD | TPM_BOTTOMALIGN | TPM_RIGHTBUTTON | TPM_VERTICAL;
auto menu_item = TrackPopupMenuEx(menu, popup_menu_flags, point.x, point.y, AfxGetMainWnd()->m_hWnd, NULL);

DestroyMenu(menu);

PopupMenu显示正确，我可以使用鼠标选择菜单项。但是箭头键不起作用。

我已经使用Spy ++和m_pMainWnd获取WM_KEYUP，VK_DOWN的消息但没有任何反应。看不到WM_KEYDOWN。

我错过了什么？