在下拉菜单显示的时候, WM_INITMENUPOPUP消息被先发送以显示菜单项。MFC CFrameWnd::OnInitMenuPopup 函数遍历菜单项并为每个菜单项调用更新命令处理函数(如果有的话).菜单的外观被更新以反映它的状态(启用/禁用,选择/取消选择) 更新用户界面机制在基于对话框的应用程序中不能工作,因为CDialog没有OnInitMenuPopup 处理函数,而使用CWnd's 默认处理函数,该函数没有为菜单项调用更新命令处理函数。//xxxdlg.h afx_msg void OnInitMenuPopup(CMenu* pPopupMenu, UINT nIndex, BOOL bSysMenu);//xxxdlg.cpp BEGIN_MESSAGE_MAP(CTest6Dlg, CDialog) //{{AFX_MSG_MAP(CTest6Dlg) ON_WM_INITMENUPOPUP() //}}AFX_MSG_MAPEND_MESSAGE_MAP()void CTest6Dlg::OnInitMenuPopup(CMenu* pPopupMenu, UINT nIndex, BOOL bSysMenu) { CDialog::OnInitMenuPopup(pPopupMenu, nIndex, bSysMenu); // TODO: Add your message handler code here ASSERT(pPopupMenu != NULL); // Check the enabled state of various menu items. CCmdUI state; state.m_pMenu = pPopupMenu; ASSERT( state.m_pOther == NULL ); ASSERT( state.m_pParentMenu == NULL ); // Determine if menu is popup in top-level menu and set m_pOther to // it if so (m_pParentMenu == NULL indicates that it is secondary popup). HMENU hParentMenu; if (AfxGetThreadState()->m_hTrackingMenu == pPopupMenu->m_hMenu) state.m_pParentMenu = pPopupMenu; // Parent == child for tracking popup. else if ((hParentMenu = ::GetMenu(m_hWnd)) != NULL) { CWnd* pParent = this; // Child windows don't have menus--need to go to the top! if (pParent != NULL && (hParentMenu = ::GetMenu( pParent->m_hWnd )) != NULL) { int nIndexMax = ::GetMenuItemCount(hParentMenu); for (int nIndex = 0; nIndex < nIndexMax; nIndex++) { if (::GetSubMenu(hParentMenu, nIndex) == pPopupMenu->m_hMenu) { // When popup is found, m_pParentMenu is containing menu. state.m_pParentMenu = CMenu::FromHandle(hParentMenu); break; } } } } state.m_nIndexMax = pPopupMenu->GetMenuItemCount(); for ( state.m_nIndex = 0; state.m_nIndex < state.m_nIndexMax; state.m_nIndex++ ) { state.m_nID = pPopupMenu->GetMenuItemID(state.m_nIndex); if (state.m_nID == 0) continue; // Menu separator or invalid cmd - ignore it. ASSERT(state.m_pOther == NULL); ASSERT(state.m_pMenu != NULL); if (state.m_nID == (UINT)-1) { // Possibly a popup menu, route to first item of that popup. state.m_pSubMenu = pPopupMenu ->GetSubMenu(state.m_nIndex); if ( state.m_pSubMenu == NULL || ( state.m_nID = state.m_pSubMenu->GetMenuItemID(0)) == 0 || state.m_nID == (UINT)-1) { continue; // First item of popup can't be routed to. } state.DoUpdate(this, TRUE); // Popups are never auto disabled. } else { // Normal menu item. // Auto enable/disable if frame window has m_bAutoMenuEnable // set and command is _not_ a system command. state.m_pSubMenu = NULL; state.DoUpdate(this, FALSE); } // Adjust for menu deletions and additions. UINT nCount = pPopupMenu ->GetMenuItemCount(); if ( nCount < state.m_nIndexMax ) { state.m_nIndex -= (state.m_nIndexMax - nCount); while ( state.m_nIndex < nCount && pPopupMenu->GetMenuItemID( state.m_nIndex ) == state.m_nID ) { state.m_nIndex++; } } state.m_nIndexMax = nCount; }}
更新用户界面机制在基于对话框的应用程序中不能工作,因为CDialog没有OnInitMenuPopup 处理函数,而使用CWnd's 默认处理函数,该函数没有为菜单项调用更新命令处理函数。//xxxdlg.h
afx_msg void OnInitMenuPopup(CMenu* pPopupMenu, UINT nIndex, BOOL bSysMenu);//xxxdlg.cpp
BEGIN_MESSAGE_MAP(CTest6Dlg, CDialog)
//{{AFX_MSG_MAP(CTest6Dlg)
ON_WM_INITMENUPOPUP()
//}}AFX_MSG_MAPEND_MESSAGE_MAP()void CTest6Dlg::OnInitMenuPopup(CMenu* pPopupMenu, UINT nIndex, BOOL bSysMenu) { CDialog::OnInitMenuPopup(pPopupMenu, nIndex, bSysMenu); // TODO: Add your message handler code here ASSERT(pPopupMenu != NULL); // Check the enabled state of various menu items. CCmdUI state; state.m_pMenu = pPopupMenu; ASSERT( state.m_pOther == NULL ); ASSERT( state.m_pParentMenu == NULL ); // Determine if menu is popup in top-level menu and set m_pOther to // it if so (m_pParentMenu == NULL indicates that it is secondary popup). HMENU hParentMenu; if (AfxGetThreadState()->m_hTrackingMenu == pPopupMenu->m_hMenu) state.m_pParentMenu = pPopupMenu; // Parent == child for tracking popup. else if ((hParentMenu = ::GetMenu(m_hWnd)) != NULL) { CWnd* pParent = this; // Child windows don't have menus--need to go to the top! if (pParent != NULL && (hParentMenu = ::GetMenu( pParent->m_hWnd )) != NULL) { int nIndexMax = ::GetMenuItemCount(hParentMenu); for (int nIndex = 0; nIndex < nIndexMax; nIndex++) { if (::GetSubMenu(hParentMenu, nIndex) == pPopupMenu->m_hMenu) { // When popup is found, m_pParentMenu is containing menu. state.m_pParentMenu = CMenu::FromHandle(hParentMenu); break; } } } } state.m_nIndexMax = pPopupMenu->GetMenuItemCount(); for ( state.m_nIndex = 0; state.m_nIndex < state.m_nIndexMax; state.m_nIndex++ ) { state.m_nID = pPopupMenu->GetMenuItemID(state.m_nIndex); if (state.m_nID == 0) continue; // Menu separator or invalid cmd - ignore it. ASSERT(state.m_pOther == NULL); ASSERT(state.m_pMenu != NULL); if (state.m_nID == (UINT)-1) { // Possibly a popup menu, route to first item of that popup. state.m_pSubMenu = pPopupMenu ->GetSubMenu(state.m_nIndex); if ( state.m_pSubMenu == NULL || ( state.m_nID = state.m_pSubMenu->GetMenuItemID(0)) == 0 || state.m_nID == (UINT)-1) { continue; // First item of popup can't be routed to. } state.DoUpdate(this, TRUE); // Popups are never auto disabled. } else { // Normal menu item. // Auto enable/disable if frame window has m_bAutoMenuEnable // set and command is _not_ a system command. state.m_pSubMenu = NULL; state.DoUpdate(this, FALSE); } // Adjust for menu deletions and additions. UINT nCount = pPopupMenu ->GetMenuItemCount(); if ( nCount < state.m_nIndexMax ) { state.m_nIndex -= (state.m_nIndexMax - nCount); while ( state.m_nIndex < nCount && pPopupMenu->GetMenuItemID( state.m_nIndex ) == state.m_nID ) { state.m_nIndex++; } } state.m_nIndexMax = nCount; }}