How to use accelerator keys and a main menu on the dialog box in Visual C++

Many applications use a modal dialog box as the main application window. Applications that use this technique may also include a main menu on the dialog box. Typically, one or more of the menu items has a keyboard accelerator associated with it. This article describes the steps that are required to add a menu and keyboard accelerators to an MFC Application Wizard dialog box-based application.

A typical application that is developed for the Microsoft Windows operating system by using Visual C++ and the Microsoft Windows Software Development Kit (SDK) and that uses keyboard accelerators calls the TranslateAccelerator() function in its main message loop. However, when you use a modal dialog box as the main window, the application does not have a main message loop; instead, the application uses the dialog box manager message loop (built into Windows) to translate and dispatch messages. Of course, because this message loop is not designed to process accelerators, it does not call the TranslateAccelerator() function.

To process accelerator keys in a modal dialog box in MFC, you must override the CWinApp::ProcessMessageFilter() function. The framework calls ProcessMessageFilter() before it processes a message.

To modify an MFC Application Wizard dialog box-based application type in Visual C++ .NET to correctly process accelerator keys, follow these steps:

1. In Visual Studio .NET, create a new MFC application. In the left pane of the MFC Application Wizard, click Application Type, and then make sure that Application type is set to Dialog based.
2. In Resource view, double-click the dialog resource to open the dialog resource editor. The resource ID of the dialog resource is similar to IDD_MYPROJECT_DIALOG (where MYPROJECT is the name that you gave your application project when you created it).
3. With the dialog resource open in the dialog resource editor, locate the Properties window. Edit the dialog box Border property and specify the Thin border style. This step is required for a dialog box that contains a menu.
4. Create a new menu resource that contains a top-level entry named &File and a menu item named &Exit\tCTRL+E (CTRL+X is usually associated with cutting text, so CTRL+E is used instead).
5. In the menu editor, click the newly created Exit menu item. In the Properties window, make sure that the ID property for the Exit menu item is set to ID_FILE_EXIT.
6. Associate the new menu with the dialog box by entering the menu ID in the dialog resource Menu property. Open the dialog editor for the dialog resource and find the Menu property in the Properties window. Set it to the resource ID that you created for the menu in step 4. To do this, click the drop-down list in the Menu property row, and then click to select the resource ID for the menu in the list.
7. In the menu editor, right-click &Exit\tCTRL+E, and then click Add Event Handler.
8. In the Event Handler Wizard, select the COMMAND message type. In the Class list, select the CDialog derived main class for the handler to be generated in. Make sure that the function handler name is appropriate, and then click Add and Edit to create the menu item event handler.
9. Insert the following line in the function Exit menu item event handler method that is generated in step 8:

   PostMessage(WM_COMMAND, IDOK, 0L);
   					

   This produces the same effect as clicking OK when the user clicks Exit on the File menu. Clicking OK closes your dialog box application.
   
   
10. Create a new accelerator resource and associate the CTRL+E key combination with ID_FILE_EXIT. Save your changes.
11. Edit the Stdafx.h file to declare the following global variables after the #include statements:

    extern HWND    ghDlg;          // Handle to main dialog box.
    extern HACCEL  ghAccelTable;   // Handle to accelerator table.
    					

12. In the .cpp file that contains the CWinApp derived class implementation (usually the .cpp file with the same base name as your project name), add the following global variable initializations:

    HWND    ghDlg = 0;          // Handle to main dialog box.
    HACCEL  ghAccelTable = 0;   // Handle to accelerator table.
    					

13. In the main CDialog derived class (not the dialog class that implements the default About dialog box), find the OnInitDialog() method. If necessary, you can add an override for the OnInitDialog() method. To do this, click to select the CDialog derived class in the Class View window, and then click Overrides in the Properties window. Find the OnInitDialog row and click the right column. If OnInitDialog() is not overridden for this class, you have the option to create an override.
14. Edit the function that you added earlier to include the following line of code:

    ghDlg = m_hWnd;
    					

15. In the .cpp file that contains the CWinApp derived implementation, find the InitInstance() class method. Add the following line immediately after the call to the base class CWinApp::InitInstance():

    ghAccelTable = LoadAccelerators(AfxGetInstanceHandle(),
    MAKEINTRESOURCE(IDR_ACCELERATOR1));
    					

    NOTE: The resource ID that is used here (IDR_ACCELERATOR1) is the ID of the accelerator table resource that is added in step 10.
    
    
16. Add an override to the CWinApp derived class for the ProcessMessageFilter() class method. To do this, in the Class View window, select the CWinApp derived class in your project. Then, in the Properties window, click Overrides. Find the ProcessMessageFilter row in the Properties window and select the right-most column of that row. Click the drop-down arrow, and then click the option to add an override for the ProcessMessageFilter method.
17. Edit the ProcessMessageFilter() method override so that it has the following implementation:

    BOOL CMyProjectApp::ProcessMessageFilter(int code, LPMSG lpMsg)
           {
              if (code < 0)
                 CWinApp::ProcessMessageFilter(code, lpMsg);
    
              if (ghDlg && ghAccelTable)
                 {
                 if (::TranslateAccelerator(ghDlg, ghAccelTable, lpMsg))
                    return(TRUE);
                 }
    
             return CWinApp::ProcessMessageFilter(code, lpMsg);
          }
    					

18. Compile and run the application. Note that it has a menu. When you click Exit on the File menu or press CTRL+E, the application closes, as expected.