HelpHook - Remarks

Help-processing is done in two stages. The first stage is the creation of the WM_HELP message. This is done:

• From a WM_CHAR message by ACCELERATOR table translation, when the HELP accelerator option is specified.

• From an action-bar selection, when the MIS_HELP style is specified on the action-bar button.

• From a dialog-box push button, when the BS_HELP style is specified on the push button.

• From a message box, when the MB_HELP style is specified on the message box.

The second stage of processing of help is the processing of the WM_HELP message.

The frame window procedure sees the WM_HELP message because the frame is usually the active window. It processes the WM_HELP message as follows:

• If the window with the focus is the FID_CLIENT frame control, it passes WM_HELP to the FID_CLIENT window.

• If the parent of the window with the focus is the FID_CLIENT frame control, it calls the help hook, specifying:

  usMode = HLPM_WINDOW idTopic = frame-window id
  idSubTopic = focus-window id.

  
  If the parent of the focus window is not the FID_CLIENT frame control (for example, it may be the frame itself, or a second-level dialog control), it calls the hook, specifying:

  usMode = HLPM_WINDOW
  idTopic = focus-window parent id
  idSubTopic = focus-window id.

  The message box window procedure sees the WM_HELP message, because it subclasses the frame window. It processes the WM_HELP message by calling the help hook, specifying:

  usMode = HLPM_MESSAGE idTopic = message id
  idSubTopic = control id.

  The menu window procedure sees the WM_HELP message because it runs a modal loop. It processes the WM_HELP message by calling the help hook, specifying:

  usMode = HLPM_MENU idTopic = menu id of pulldown
  idSubTopic = menu id of item.

  The WinDefWindowProc function sees the WM_HELP message for a FID_CLIENT window if the client does not handle it itself. It calls the help hook, specifying:

  usMode = HLPM_WINDOW idTopic = active-window id
  idSubTopic = focus-window id.

  An application sees the WM_HELP message in its dialog procedure. The application can ignore the WM_HELP message, in which case the frame-window procedure action occurs (as described above) or it can simulate a call to the help hook itself, using:

  usMode = HLPM_APPLICATION idTopic = any value
  idSubTopic = any value.

  The input focus is never given to any of the standard frame controls, so help for these cannot be obtained.

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