Allegro CL version 10.1
Unrevised from 10.0 to 10.1.
10.0 version

About adding context-sensitive help to your Common Graphics application

This document contains the following sections:

1.0 Displaying help
   1.1 Comprehensive help
   1.2 Quick help
2.0 Triggering help
   2.1 Triggering help automatically
   2.2 Triggering help on request
3.0 Deciding what to provide help on
   3.1 Help on the selected window
   3.2 Help on the selected data object
4.0 An example of providing help
5.0 Dealing with an unexpected error in an application

This document describes techniques that can be used in Common Graphics to allow the end user to quickly get help on whatever feature of your application they happen to be using at any moment. Typically, it's important to add such context-sensitive help to your application so that your users are able to easily discover all of the wonderful features that you have designed and to get quick reminders about features that they've already learned.

1.0 Displaying help

This section describes how to display help once you've decided what to show help on. Further sections cover how to trigger the displaying of help and how to decide what to provide help on.

1.1 Comprehensive help

Comprehensive help is useful for initially learning about a feature. Quick help, covered below, is better for providing quick reminders about features that have already been learned. The techniques covered here for comprehensive help are HTML, WinHelp, and rich text.


A popular and easy way to display comprehensive help is to show it in a web browser. In CG, an application can display an HTML file by simply calling invoke-html-browser on a pathname or namestring of an HTML file that you have prepared.

This facility requires either that the end user has established Internet Explorer or Netscape Navigator as their default HTML browser, or that they are currently running one of those programs. In the unlikely event that a user does not have either of these browsers, your app could instruct them to simply download one of them. (You can detect this case by checking if invoke-html-browser returns nil.)

Common Graphics tries to expose the HTML browser after it has displayed the HTML file in it (starting up the default browser if none is running), though newer versions of Windows prevent exposing a window in another thread, and instead the browser's button in the taskbar will flash to tell the user that the browser is asking to be selected.

Allegro does not provide an HTML editor, so it is up to you to create your HTML files using whatever tool you like.


WinHelp is a standard facility for help in Windows programs, though many people have moved to HTML or XML more recently in order to maintain their master help data in a less proprietary or more forward-looking format. If you prefer WinHelp, it can be used in an Allegro application, though you must call the Windows API function for this facility directly. You must also use a third-party tool to construct the WinHelp file to distribute.

To invoke WinHelp, you just need to call the function windows:WinHelp. Below is a sample function that shows how you can call this Windows API function directly. (The def-foreign-call for WinHelp has already been set up, as with many other Windows API functions that exist as lisp functions in the "windows" package.) The function shown below does not exist in Allegro, but you may use it or something similar. To implement additional WinHelp options, refer to Microsoft's documentation.

(defun windows-help (window winhelp-file topic)
  ;; WINDOW should be any window in your application.
  ;; WINHELP-FILE should be the pathname or namestring of a winhelp file.
  ;; TOPIC should be either a string naming a "key" in the winhelp file,
  ;;   or the symbol :index to display the winhelp file's index,
  ;;   or the symbol :close to close the winhelp window.
  (let* ((key? nil)
         (type (case topic
                 (:index win:HELP_FINDER)
                 (:close win:HELP_QUIT)
                 (t (setq key? t) win:HELP_KEY))))
    (excl:with-native-string (native-path-string (namestring winhelp-file))
      (excl:with-native-string (native-topic-string (if key? topic ""))
        (win:WinHelp (cg:handle window) native-path-string type
                     (if key? native-topic-string 0))))))

Allegro does not provide any tools for creating WinHelp files, so you need to use other tools to create them.

Rich text

Another option is to use rich text. Common Graphics includes a rich-edit widget, and so displaying help in such a widget allows you to integrate help anywhere in the window hierarchy of your Common Graphics application, rather than as a separate top-level HTML browser or WinHelp window over which your application has less control. The rich-edit control does not support multiple columns or pixmaps, but does support such things as multiple font faces and sizes, colored text, bulleted lists, and different indentation and justification in each paragraph, which can go a long way.

You can create rich text documents to be read into a Common Graphics rich-edit control either in a word processor such as Word or Wordpad, or in a Common Graphics rich-edit control. To try editing rich text in the IDE, invoke the File | New Form command and select rich-edit-dialog from the list of window types. Running this form allows you to start editing rich text immediately.

A non-standard rich text feature that Common Graphics provides is the ability to add colored hypertext links to a rich text document (see find-links), similar to HTML links. You will need to use a Common Graphics rich-edit-dialog to add the links, rather than a third-party word processor.

See cg-rich-text.htm for an introduction to Common Graphics's rich text functionality.

1.2 Quick help

Common Graphics makes it easy to display quick reminders to the user either as status-bar messages or as tooltips.

Status bar messages

A status bar is a narrow area along the bottom of a window into which short messages can be displayed. Common Graphics offers two types of status bars:

When designing a form interactively, you can add a status bar to any window by toggling the window's status-bar property in the inspector. The resulting status bar will always be a common-status-bar. Call add-common-status-bar to add a common-status-bar programmatically, or add-status-bar if the multi-line model is preferred.

You can display text in a status bar at run time by calling either status-bar-message (passing in the status bar itself) or window-message (passing in the window that the status-bar is on; this is typically more convenient). Calling (setf parts) on a common-status-bar will divide it into sections for multiple short messages.


A tooltip window is a small window that pops up momentarily, usually as a reminder of what an interface component does.

A tooltip can be implemented for any control (dialog-item) by simply setting its tooltip property to an appropriate short string. The built-in behavior of Common Graphics will cause a small tooltip window to appear when the mouse cursor has been over the control for a short time. You can customize this default behavior by modifying configuration options such as show-tooltips, tooltip-delay, and tooltip-vertical-offset.

2.0 Triggering help

The preceding section covered how to display help in various ways. This section covers how to enable the user to invoke help. This can be done either automatically, where a gesture that a user is making for some other reason is also used to display help, or on request, where the user makes an explicit request for help.

2.1 Triggering help automatically

On tooltip delay

When using tooltips, there is nothing you need to do to trigger showing the tooltip window, since the tooltips facility handles this for you.

But if you would like to show additional help at the time that a tooltip is triggered, you can add a show-tooltip method, which will always be called at this time. Be sure not to overwrite the existing primary method on dialog-item, though, since that would disable all tooltips. For example, the following :after method would display the name and the help-string property of a control in the status-bar of control's parent window (if it has one) at the same time that the tooltip window appears. (The IDE uses a similar method, but it is not built into a Common Graphics app unless you add such a method yourself.)

(defmethod show-tooltip :after ((control dialog-item))
  (window-message (parent control)
    "~a --- ~a" (name control)(or (help-string control)
                                  "MISSING HELP STRING")))

Note that show-tooltip is called even when the control has no tooltip, so the above method will display status-bar help after the mouse cursor pauses briefly over a control even if it has no tooltip.

Note also that Common Graphics does not make any use of the help-string property of controls itself; it is simply provided as a handy hook where you can place help strings to display whenever and however you like. Typically a help-string is displayed in a status bar, and is longer than a tooltip.

On entering a window or widget

To trigger help when the mouse cursor moves into a control or window, an on-mouse-in event-handler can be added to a control, or a mouse-in method can be written for a window class or a hotspot class. This allows triggering help immediately rather than after the tooltip pause. This technique can also be applied to arbitrary windows and to hotspots rather than to controls only.

The following example would show a status bar message whenever the mouse moves into a window.

(defmethod mouse-in :after ((window basic-pane) buttons mouse-out-object)
  (window-message *my-main-window*
    "Moving from ~a into ~a." (name mouse-out-object)(name window)))

On highlighting a menu-item

The generic function menu-item-highlighted is called whenever the user moves the mouse over a menu-item to highlight it. You can add a menu-item-highlighted method to display help on the menu-item at this time. Built-in methods will display the help-string of a menu-item in the status-bar of the menu's owner window if there is a status-bar there. If you'd prefer to show some other sort of help on menu-items, then you can override the built-in menu-item-highlighted methods.

On changing a value in a control

It may be useful to display status bar messages when the value of a control changes. This can be done easily by adding a call to window-message in the on-change functions of the controls. This is especially useful for controls such as a single-item-list and outline that list options that a user can click on in order to see the help string for each one before committing to any particular choice.

2.2 Triggering help on request

You can add menu commands, global keyboard shortcuts, or buttons that the user can use to invoke help explicitly.

Menu-bar commands (with F1 as a keyboard shortcut)

The standard way to allow users to explicitly request help is to add one or more menu-items to the application's menu-bar, typically on a Help menu at the right end of the menu-bar. And a convention in Windows is that the keyboard shortcut for the most basic help command in the application is the F1 key. Specify the :event-synonym initarg to make-instance as the symbol vk-f1 when creating a menu-item to give it this keyboard shortcut.

Shortcut pop-up menus

Help commands can also be added to pop-up menus. A convention in Windows is to add commands for quick access to a pop-up-menu invoked by clicking the right mouse button in the interior of a window. This can be implemented in a general way by adding a mouse-right-down method that calls open-menu and pop-up-menu. Or using shortcut-commands and pop-up-shortcut-menu may be somewhat more convenient for typical shortcut menus.

Global keyboard accelerators

If your application includes top-level windows that are not children of your main top-level window that has a menu-bar, then you may want to add global keyboard accelerators for help commands that should always be available. See add-global-keyboard-accelerator.

context-sensitive-help methods

An alternative to adding an explicit menu-item or global keyboard accelerator for the common F1 gesture for context-sensitive help is to add one or more context-sensitive-help methods. That generic function is called whenever the user presses the F1 key, and also when the user uses the question mark button on the title-bar of a window that has been given the help-button property.


Another option, of course, is to have a simple button control on each dialog whose title is Help and which invokes help on the dialog that it is on. Just add an on-change event-handler to the button that invokes the appropriate help.

3.0 Deciding what to provide help on

When the user invokes a general command that asks for help on the current context, you must decide what object they want contextual help on. This is typically the dialog or other window that they are currently working in, or perhaps the currently selected application value in that window. The first two commands in the IDE's Help menu, for example, provide options for those two cases.

3.1 Help on the selected window

The function selected-window can be called to find what window the user is currently working in. It may be first called on the screen to find which top-level window is selected, or you may know that already (either by keeping your main window in a global variable or by noting the owner window of the menu that was invoked). If this top-level window is just a container for other more interesting windows, calling selected-window on that window will tell you what child window is selected within it.

An alternative is to call get-focus, typically as (get-focus (screen *system*)), to directly ask which child window has the keyboard focus.

3.2 Help on the selected data object

The function selected-object (or related functions such as selected-symbol, selected-class, and selected-string) may be used to find the application value that is considered to be selected currently in a control or window. When called on a control, the built-in methods will likely return a usable value. There are no built-in methods for non-control windows, but an application can write a selected-object method for any window to return a value in some application-specific way.

4.0 An example of providing help

The remainder of this document is a basic example that illustrates many of the points covered above. It displays a window with a menu-bar, a common-status-bar, and a single-item-list control. Choosing commands either from the menu-bar or from the right-button shortcut menu will display help strings in the status-bar.

Evaluate (help-menu-example) to run the example.

(in-package :cg-user)

;;; Define our own window and widget subclasses so that
;;; we can add mouse-right-down methods to them below.

(defclass my-main-window (frame-window)())

(defclass my-single-item-list (single-item-list)())

;; Call this function to create the example's window
;; and give it a menu-bar and a common-status-bar.

(defun help-menu-example ()
  (let* ((window (make-window :my-main-window
                   :class 'my-main-window
                   :title "Menus and Help Options"
                   :exterior (make-box 100 200 600 500)
                   :scrollbars nil
                   (list (make-instance 'my-single-item-list
                           :name :list
                           :range '(one two three)
                           :value 'one
                           :tooltip "The first three."
                           :help-string "Pick a number.  Any number."
                           :on-mouse-in 'show-the-help-string
                           :on-mouse-out 'clear-the-status-bar
                           :on-change 'my-on-change
                           :left 20 :top 60
                           :width 100 :height 80)))))
    (add-common-status-bar window)
    ;; Give the window a menu-bar that has a single Help pull-down
    ;; menu, which in turn has two help commands on it.
     ;; This is the menu-bar's menu-item for the Help pull-down menu.
     (list (make-instance 'menu-item
             :name :help-menu
             :title "~Help"
             :help-string "This pull-down menu contains help commands."
             :value (open-menu
                     ;; This is the Help pull-down menu itself.
                     (list (make-instance 'menu-item
                             :name :help-on-value
                             :title "~Help on Value"
                             :value 'help-on-value
                             :help-string "Shows help on the selected value."
                             :event-synonym 'vk-f1)
                           (make-instance 'menu-item
                             :name :help-on-dialog
                             :title "Help on ~Dialog"
                             :value 'help-on-dialog
                             :help-string "Shows help on the selected window."
                             :event-synonym '(control-key vk-f1)))
                     'pull-down-menu (screen *system*)
                     :on-click 'funcall-menu-item-with-window)))
     'menu-bar window)

(defun help-on-value (window)
  "Called by the Help on Value menu command."
  ;; Find the selected value in the single-item-list on the main window.
  (let* ((value (selected-object (dialog-item (selected-window window)))))
    ;; Display information about this value in the window's status-bar.
    (window-message window "~a --- ~a"
      (case value
        (one "The loneliest number.")
        (two "The second loneliest number.  Sometimes as bad as one.")
        (three "The number of dogs required for adequate warmth tonight.")
        (t "No value selected.")))
    #+later ;; This could be used if the HTML pages existed.
     (merge-pathnames (format nil "help-dir/~a.html" value)
                      ;; This returns the directory of the running
                      ;; executable lisp (IDE or standalone app).
                      (translate-logical-pathname "sys:")))))

(defun help-on-dialog (window)
  "Called by the Help on Window menu command."
  (window-message window "~a"
    "This window implements the famous CG Help example."))

(defun show-the-help-string (widget buttons mouse-out-window)
  "Called when the mouse moves into WIDGET."
  (declare (ignore buttons mouse-out-window))
  (window-message (parent widget) "~a" (help-string widget)))

(defun clear-the-status-bar (widget buttons mouse-in-window)
  "Called when the mouse moves out of WIDGET."
  (declare (ignore buttons mouse-in-window))
  (window-message (parent widget) ""))

(defun my-on-change (widget new-value old-value)
  "Called when the value of WIDGET has changed."
  (window-message (parent widget) "Widget ~s goes from ~s to ~s."
    (name widget) new-value old-value))

(defmethod mouse-right-down ((window my-main-window)
                             buttons cursor-position)
  ;; This is called when the user right-clicks the main window interior.
  (my-mouse-right-down window buttons cursor-position))

(defmethod mouse-right-down ((control my-single-item-list)
                             buttons cursor-position)
  ;; This is called when the user right-clicks the single-item-list.
  (my-mouse-right-down (parent control) buttons cursor-position))

(defun my-mouse-right-down (window buttons cursor-position)
  "Pops up a shortcut menu for this application."
  (declare (ignore buttons cursor-position))
  (let* ((menu (open-menu
                (list (make-instance 'menu-item
                        :name :help-on-value
                        :title "~Help on Value"
                        :value 'help-on-value
                        :help-string "Shows help on the selected value.")
                      (make-instance 'menu-item
                        :name :help-on-dialog
                        :title "Help on ~Dialog"
                        :value 'help-on-dialog
                        :help-string "Shows help on the selected window."))
                'pop-up-menu (screen *system*)))
        ;; If the user selected a choice from the menu, call the
        ;; function which is the select menu-item's value.
        (when (setq value (pop-up-menu menu window))
          (funcall value window))
      ;; Be sure to close temporarily-used menus to free up
      ;; operating system menu resources.
      (close menu))))

(defmethod redisplay-window ((window my-main-window) &optional box)
  (declare (ignore box))
  (call-next-method) ;; draw the background
  ;; Draw this string in the window whenever it is uncovered.
   window "Right-click to see the shortcut menu."
   nil nil (make-box 40 180 400 200) :left :top))


5.0 Dealing with an unexpected error in an application

If an unexpected error is signaled while your application is running, it is preferable that it be handled so that minimal user data is lost and the chance of recovery is maximized. The app property default-error-handler-for-delivery allows you to specify a function that will be called, with the signaled condition as an argument, that can deal with the error (although exiting the program after attempting to save data and collect useful debugging information is often the only reasonable action).

See the description of the property for more details. The defaul function simply displays a dialog that tells the user an unexpected error has occurred and exits Lisp.

Copyright (c) 1998-2022, Franz Inc. Lafayette, CA., USA. All rights reserved.
This page was not revised from the 10.0 page.
Created 2019.8.20.

Allegro CL version 10.1
Unrevised from 10.0 to 10.1.
10.0 version