How to Create Context-Sensitive HTML Help in an MFC Application

MORE INFORMATION

Perform the following steps in your MFC Visual C++ Application:

1. Add an array of ID pairs to your application to map control IDs to help context IDs. The last pair should be 0's. For example:

         static const DWORD aMenuHelpIDs[] =
         {
            ID_FILE_NEW,  IDH_FILE_NEW ,
            ID_FILE_OPEN, IDH_FILE_OPEN ,
            ID_FILE_SAVE, IDH_FILE_SAVE ,
            ID_EDIT_CUT,  IDH_EDIT_CUT,
            ID_EDIT_COPY, IDH_EDIT_COPY,
            ID_EDIT_PASTE, IDH_EDIT_PASTE,
            ID_FILE_PRINT, IDH_FILE_PRINT,
            ID_APP_ABOUT,  IDH_APP_ABOUT,
            ID_FILE_PRINT_PREVIEW, IDH_FILE_PRINT_PREVIEW,
            0,    0
         };
   						

   In the previous example, each control ID is followed by its corresponding help ID.
2. Underneath the array of ID pairs, declare a variable that will determine the total number of ID pairs. For example:

         // Subtract 1 from the total number of ID pairs to account
         // for the NULL pair at the end of the array.
         DWORD numHelpIDs = (sizeof(aMenuHelpIDs)/sizeof(DWORD))/2 - 1
   					

3. Override the CWinApp::Winhelp method to call the HTML Help API instead of WinHelp. For example:

         void CTestApp::WinHelp( DWORD dwData, UINT nCmd )
         {
         DWORD i;
         switch (nCmd)
         {
         case HELP_CONTEXT:
   
            // If it is a help context command, search for the
            // control ID in the array.
            for (i= 0; i < numHelpIDs*2; i+=2)
            {
              if (aMenuHelpIDs[i] == LOWORD (dwData) )
              {
                i++;  // pass the help context id to HTMLHelp
                HtmlHelp(m_pMainWnd->m_hWnd,"sample.chm",
                   HH_HELP_CONTEXT,aMenuHelpIDs[i]);
                return;
              }
            }
   
            // If the control ID cannot be found,
            // display the default topic.
            if (i == numHelpIDs*2)
            HtmlHelp(m_pMainWnd->m_hWnd,"sample.chm",HH_DISPLAY_TOPIC,0);
            break;
            }
         }
   						

   NOTE: In the previous example, Sample.chm must be in the same folder as the MFC application project file because no path is specified.
4. Include a prototype for the WinHelp function as follows:

         virtual void WinHelp( DWORD dwData, UINT nCmd = HELP_CONTEXT );
   					

5. Include a file containing the context-sensitive help ID definitions. The numeric values of these IDs must match the values defined in the [MAP] section of the HTML Help project file. The following is an example of how the context help IDs are defined:

         #define IDH_FILE_NEW   1
         #define IDH_FILE_OPEN  2
         #define IDH_FILE_SAVE  3
         #define IDH_EDIT_CUT   4
         #define IDH_EDIT_COPY  5
         #define IDH_EDIT_PASTE 6
         #define IDH_FILE_PRINT 7
         #define IDH_APP_ABOUT  8
         #define IDH_FILE_PRINT_PREVIEW 9
   					

6. Rebuild the project.

F1 help may come up twice, if there is an entry for ID_HELP in the accelerator table (as explained in BUG: WinHelp Called Twice).

For the "What's this" help, the MFC framework sends a WM_HELPHITTEST message (see TN028 for more details) to each window, starting with the window under the mouse cursor and moving up the hirearchy. If none of the windows handle this message, the CFrameWnd handler for this message returns the general topic-value, which is passed on to CWinApp::WinHelp in dwData.

To get "What's this" help to work the way F1 help works (which is how it works in Dialogs according to DS_CONTEXTHELP), it is necessary to provide a WM_HELPHITTEST handler. A generic one that returns the ID of the child window under the cursor could be written as follows (gleaned from CControlBar::OnHelpHitTest):

LRESULT CMyView::OnHelpHitTest(WPARAM, LPARAM lParam)
{
  ASSERT_VALID(this);

  // Find the child window ID under mouse cursor
  int nID = OnToolHitTest((DWORD)lParam, NULL);
  if (nID != -1)
    return HID_BASE_CONTROL+nID;

  nID = GetDlgCtrlID();
  return nID != 0 ? HID_BASE_CONTROL+nID : 0;
}