BUG: Enabling Accelerator Keys in Visual Basic ActiveX Controls

MORE INFORMATION

The steps below show how to set up a callback function for the EnumChildWindows() API from the MFC container application; determine the access keycode for the child windows of the Visual Basic ActiveX control; and determine which control to set the input focus to when an accelerator key is pressed:

1. Place the Visual Basic ActiveX control in an MFC dialog-based application.
2. Add a member variable named m_XControlInfo to the CDialog-derived class as below:

         #include <afxtempl.h>
   
         // Information about child controls in the Visual Basic
         // ActiveX control.
         typedef struct xcontrol_info
         {
            HWND hwnd;            // handle of child control
            char mnemonic_char;   // mnemonic character key for the control
         }
         XCONTROL_INFO;
   
         class CTestVBDlg : public CDialog
         {
         ...
            // Array of info for child controls.
            CArray<XCONTROL_INFO, XCONTROL_INFO> m_XControlInfo;
         ...
         }
   						

3. Enumerate all the child windows of the Visual Basic ActiveX control in OnInitDialog() of your CDialog-derived class. This callback function will be called for each child control in the ActiveX control. The HWND and the mnemonic character keycode of the child control will be stored in the m_XControlInfo array:

         // Callback function for EnumChildWindows() API
         BOOL CALLBACK EnumActiveXControlChildProc(HWND hwnd, LPARAM lParam)
         {
            CArray<XCONTROL_INFO, XCONTROL_INFO>* arr =
            (CArray<XCONTROL_INFO, XCONTROL_INFO>*)lParam;
   
            CString str;
            CWnd*   control = CWnd::FromHandle(hwnd);
            control->GetWindowText(str);
            int index = str.Find('&');   // look for mnemonic
                                         // character keycode
            if (index > -1)
               {
                  XCONTROL_INFO info;
                  info.hwnd = hwnd;
                  info.mnemonic_char = str[index+1];
                  arr->Add(info);
               }
   
            return TRUE;
         }
   
         BOOL CTestVBDlg ::OnInitDialog()
         {
            CDialog::OnInitDialog();
            ...
   
            // Setup a callback function for EnumChildWindows() API to
            // enumerate all child windows of the ActiveX control.
            HWND hcontrol = GetDlgItem(IDC_VB_CONTROL1)->GetSafeHwnd();
            EnumChildWindows(hcontrol, EnumActiveXControlChildProc,
               (LPARAM) &m_XControlInfo);
            return TRUE;
         }
   						

4. Modify the OnSysCommand() function of your CDialog-derived class for determining which child window in your ActiveX control should receive the input focus when an accelerator key is pressed:

         void CTestVBDlg ::OnSysCommand(UINT nID, LPARAM lParam)
         {
            if ((nID & 0xFFF0) == IDM_ABOUTBOX)
            {
                  CAboutDlg dlgAbout;
                  dlgAbout.DoModal();
            }
            else
            {
               // If user pressed an accelerator keystroke, loop through the
               // array to find out if it is one of the access keys for a
               // child control in the Visual Basic ActiveX control.
               BOOL  trap_accel = nID == SC_KEYMENU;
               if (trap_accel)
               {
                  int size =    m_XControlInfo.GetSize();
                  for (int i = 0; i < size; i++)
                  {
                     if (toupper(LOWORD(lParam)) ==
                        toupper(m_XControlInfo[i].mnemonic_char))
                     {
                        HWND child = m_XControlInfo[i].hwnd;
                        ::SetFocus(child);
   
                        ::SendMessage(child, BM_CLICK, 0, 0L);  // OPTIONAL!!!
                     }
                  }
               }
   
            if (!trap_accel)
            CDialog::OnSysCommand(nID, lParam);
            }
         }
   						

Steps to Reproduce Behavior

1. Create an ActiveX control with Visual Basic 5.0. The ActiveX control has two Command buttons as its child windows called "Button &A" and "Button &B," where A and B are the access keys for the buttons.
2. Use the control in a Visual Basic form and note the access keys work as expected.
3. Use the control in an MFC container application and note the access keys do not work. You will only get a message beep sound when the access key is pressed.