A recent CSSM thread about implementing a system-wide GUI help system ^[1] got me working on a post to present Matlab’s built-in hidden/unsupported mechanism for context-sensitive help. There are many different ways in which such a system can be implemented (read that thread for some ideas), so Matlab users are by no means limited to Matlab’s built-in implementation. However, the built-in system certainly merits consideration for its simplicity and usefulness.
We start with Matlab’s cshelp function (%matlabroot%\toolbox\matlab\uitools\cshelp.m). cshelp is semi-documented, meaning that it has a help section but no doc, online help or official support. This useful function was grandfathered (made obsolete) in Matlab 7.4 (R2007a) for an unknown reason and to my knowledge without any replacement. cshelp is entirely based on m-code (no hidden internal or Java code) and is surprisingly compact and readable.
cshelp basically attaches two new properties (CSHelpMode and CSHelpData) to the specified figure (this is done using the schema.prop mechanism which will be described in a separate post), temporarily disables all active uicontrols, modifies the figure’s WindowButtonDownFcn callback and sets the mouse cursor (using setptr – another semi-documented function) to an arrow with a question mark.
Clicking any object in the figure’s main area (beneath the toolbar), causes the modified WindowButtonDownFcn callback to run whatever is stored in the figure’s HelpFcn property (string, @function_handle or {@function_handle, params, …} format). Here is a simple example taken from CSSM ^[2] (thanks Jérôme):

Hfcn = 'str=get(gco,''type''); title([''Type :'' str])';
set(gcf,'HelpFcn',Hfcn);
th = 0:0.314:2*pi;
plot(th,sin(th),'r-','linewidth',4);
uicontrol('units','normalized', 'position',[.45 .02 .1 .05]);
cshelp(gcf);
set(gcf,'CSHelpMode','on');

• Set the figure’s KeyPressFcn callback property to catch events (e.g., <ESC> key presses) and reset the CSHelpMode property from within the callback
• Reset the CSHelpMode property at the end of the HelpFcn callback
• Add a CS Help entry/exit option to the figure’s Help main menu
• Add a CS Help entry/exit button to the figure toolbar

The following code sample implements all of these suggested tactics (the code to synchronize the states of the menu item and toolbar button is not presented):

% Set the  key press to exit CSHelp mode
keyFcn = ['if strcmp(get(gcbf,''CurrentKey''),''escape''), ' ...
             'set(gcbf,''CSHelpMode'',''off''); ' ...
          'end'];
set(gcf,'keyPressFcn',keyFcn);
% Exit CSHelp mode at the end of the CSHelp callback
helpFcn = 'title([''Type :'' get(gco,''type'')]); set(gcbf,''CSHelpMode'',''off'');';
set(gcf,'HelpFcn',helpFcn);
% Add a CSHelp button to the figure toolbar
% Note: retrieve the button icon from the CSHelp cursor icon
hToolbar = findall(allchild(gcf),'flat','type','uitoolbar');
oldPtr = getptr(gcf);
ptrData = setptr('help');
set(gcf, oldPtr{:});
icon(:,:,1) = ptrData{4}/2;  % Convert into RGB TrueColor icon
icon(:,:,2) = ptrData{4}/2;
icon(:,:,3) = ptrData{4}/2;
cbFcn = 'set(gcbf,''CSHelpMode'',get(gcbo,''state''))';
csName = 'Context-sensitive help';
uitoggletool(hToolbar,'CData',icon, 'ClickedCallback',cbFcn, 'TooltipString',csName);
% Add a CSHelp menu option to the Help main menu
% Note: unlike other main menus, the Help menu tag is empty, so
% ^^^^  findall(gcf,'tag','figMenuHelp') is empty... Therefore,
%       we find this menu by accessing the Help/About menu item
helpAbout = findall(gcf,'tag','figMenuHelpAbout');
helpMenu = get(helpAbout,'parent');
cbFcn = ['if strcmp(get(gcbo,''Checked''),''on''), ' ...
             'set(gcbo,''Checked'',''off''); ' ...
         'else, ' ...
             'set(gcbo,''Checked'',''on''); ' ...
         'end; ' ...
         'set(gcbf,''CSHelpMode'',get(gcbo,''checked''))'];
uimenu(helpMenu,'Label',csName,'Callback',cbFcn,'Separator','on');

Hfcn=['helpview(get(gco,''HelpTopicKey''),''CSHelpWindow'');'...
      'set(gcbf,''CSHelpMode'',''off'');' ];
set(gcf,'HelpFcn',Hfcn);
th = 0:0.314:2*pi;
hLine = plot(th,sin(th),'r-','linewidth',4);
set(hLine,'HelpTopicKey','MyCSHelpFile.html#Line');
set(gca,  'HelpTopicKey','MyCSHelpFile.html#Axes');

cshelp is by no way limited to presenting Matlab documentation: Refer to helpview‘s help section for an in-depth description of help maps and help topics. In a nutshell, helpview accepts any HTML webpage filepath (or webpage internal (#) reference), followed by optional parameter ‘CSHelpWindow’ (that indicates that the specified help page should be displayed in a stand-alone popup window rather than in the desktop’s standard Help tab), and optional extra parameters specifying the popup window’s figure handle and position. The webpage filepath parameter may be replaced by two string parameters, HelpTopicMap filepath and HelpTopicKey. Note that helpview itself is another semi-documented function.

10 Comments To "Context-Sensitive Help"

#1 Comment By Ashish Sadanadnan On August 5, 2009 @ 12:50

#2 Comment By Jason McMains On August 12, 2009 @ 05:07

#3 Comment By Yair Altman On August 27, 2009 @ 02:58

    try
        children(i).updateVisibility();
    catch
        % never mind...
    end

#4 Comment By Andy On August 17, 2009 @ 06:51

#5 Comment By Jason McMains On August 27, 2009 @ 11:39

#6 Comment By Yair Altman On August 27, 2009 @ 13:32

#7 Comment By Jason McMains On August 31, 2009 @ 11:31

#8 Comment By Dani On November 26, 2009 @ 12:09

#9 Comment By Yair Altman On November 27, 2009 @ 05:47

jDesktop = com.mathworks.mde.desk.MLDesktop.getInstance;
jTextArea = jDesktop.getMainFrame.getFocusOwner;
jClassName = 'com.mathworks.mlwidgets.help.HelpPopup';
jPosition = java.awt.Rectangle(0,0,400,300);
helpTopic = 'surf';
javaMethodEDT('showHelp',jClassName,jTextArea,[],jPosition,helpTopic);

#10 Comment By Yair Altman On November 30, 2009 @ 09:52