DOCUMENT:Q97693 07-MAY-2001 [visualc] TITLE :INFO: Dynamic Processing of WM_COMMAND Messages PRODUCT :Microsoft C Compiler PROD/VER:winnt:1.0,2.0,2.1,4.0 OPER/SYS: KEYWORDS:kbDocView kbMFC kbVC100 kbVC150 kbVC200 kbVC400 kbGrpDSMFCATL kbArchitecture ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - The Microsoft Foundation Classes (MFC), used with: - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52 - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0 ------------------------------------------------------------------------------- SUMMARY ======= The message-map mechanism provided by the Microsoft Foundation Classes (MFC) can process WM_COMMAND messages for a constant ID. However, in some cases, an application needs to process WM_COMMAND messages for an ID that is not known until run time. This can occur when an application modifies menus or dynamically creates controls at run time. To process these messages, your application must override the CCmdTarget::OnCmdMsg() function. MORE INFORMATION ================ The Microsoft Foundation Classes provide both the ON_COMMAND() and ON_UPDATE_COMMAND_UI() message-map macros to process WM_COMMAND messages. The ON_COMMAND() macro dispatches a WM_COMMAND message generated when the user selects a user interface object (for example, a control or a menu item). The ON_UPDATE_COMMAND_UI() macro updates the status of the user interface object that generates the WM_COMMAND message. Each of these macros requires a constant for the command ID. If the command ID is not known until run time, the message must be processed without using a message map. The sample code below demonstrates overriding the OnCmdMsg() member function to dynamically process messages from a dynamically-created button. The sample code processes messages for a class derived from CDocument. The command ID is stored in the m_MyButtonID member variable. The code calls the DoMyButton() member function when the user chooses the button, and calls the DoUpdateMyButton() member function when the Microsoft Foundation Classes library requests the status of the button. Sample Code ----------- BOOL CMyDocument::OnCmdMsg(UINT nID, int nCode, void * pExtra, AFX_CMDHANDLERINFO* pHandlerInfo) { // If pHandlerInfo is NULL, then handle the message if (pHandlerInfo == NULL) { // Filter the commands sent to a button the // ID of which is stored in m_MyButtonID. if (nID == m_MyButtonID) { if (nCode == CN_COMMAND) DoMyButton(); // Handles WM_COMMAND messages // sent by the button. else if (nCode == CN_UPDATE_COMMAND_UI) DoUpdateMyButton((CCmdUI*) pExtra); // Update buttons UI. return(TRUE); } } // Call the base class version of OnCommand // so the message-map can handle the message. return CDocument::OnCmdMsg(nID, nCode, pExtra, pHandlerInfo); } REFERENCES ========== MFC Technical Note 6: Message Maps. MFC Technical Note 21: Command and Message Routing. Additional query words: ====================================================================== Keywords : kbDocView kbMFC kbVC100 kbVC150 kbVC200 kbVC400 kbGrpDSMFCATL kbArchitecture Technology : kbAudDeveloper kbMFC Version : winnt:1.0,2.0,2.1,4.0 Issue type : kbinfo ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.