菜单是一个特殊的窗口，特殊在 在指定鼠标位置显示，焦点消失时，自动销毁，无任务栏图标等
我们看看，duilib是如何实现这些功能的
enum MenuAlignment{eMenuAlignment_Left = 1 << 1,eMenuAlignment_Top = 1 << 2,eMenuAlignment_Right = 1 << 3,eMenuAlignment_Bottom = 1 << 4,};
菜单类
extern const TCHAR* const kMenuElementUIInterfaceName;// = _T("MenuElement);class CMenuElementUI;class CMenuWnd : public ui::WindowImplBase{public:virtual Control* CreateControl(const std::wstring& pstrClass) override;enum PopupPosType{RIGHT_BOTTOM,RIGHT_TOP};CMenuWnd(HWND hParent = NULL);void Init(STRINGorID xml, LPCTSTR pSkinType, POINT point, PopupPosType popupPosType = RIGHT_BOTTOM); std::wstring GetWindowClassName() const; LRESULT HandleMessage(UINT uMsg, WPARAM wParam, LPARAM l