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<H2><A NAME="sec:11.2"><SPAN class="sec-nr">11.2</SPAN> <SPAN class="sec-title">Showing
help-balloons</SPAN></A></H2>
<A NAME="sec:balloon"></A>
<P><A NAME="idx:balloon:483"></A>The library <CODE>library(help_message)</CODE>
provides support for displaying
<EM>balloons</EM>. After loading this library, a <CODE>loc_still</CODE>
event causes the system to look for a <A class="" href="summary.html#class:graphical">graphical</A>
implementing the <B><CODE><-</CODE>help_message</B> method. If <B><CODE><-</CODE>help_message</B>:
tag yields a string, the library shows a little window with the message.
Moving the pointer out of the area of the graphical or pressing a button
causes the feedback window to disappear.
<P>This tenchnique is commonly used in modern interfaces to provide
feedback on the functions behind icons. See also <A class="sec" href="libdia.html">section
11.3.2</A>.
<P>In addition to registering the global event-handler, the library
defines <B><CODE>-></CODE>help_message</B> to the classes <A class="" href="summary.html#class:visual">visual</A>, <A class="" href="summary.html#class:graphical">graphical</A>
and <A class="" href="summary.html#class:menu">menu</A>.
<DL>
<DT><STRONG>visual ->help_message:</STRONG> <VAR>{tag,summary},
string*</VAR></DT>
<DD class="defbody">
Register <VAR>string</VAR> as <CODE>tag</CODE> (balloon) or extensive
help message (<CODE>summary</CODE>) for the receiving object. At the
moment
<CODE>summary</CODE> is not used.</DD>
<DT><STRONG>visual <-help_message:</STRONG> <VAR>{tag,summary}, event</VAR></DT>
<DD class="defbody">
string This message is defined to return the help-message registered
using
<B><CODE>-></CODE>help_message</B>. User-defined classes may consider
redefining this method to generate the help-message on-the-fly.
</DD>
</DL>
<P>Here is a typical usage for this library.
<PRE class="code">
:- use_module(library(help_message)).
resource(print, image, image('16x16/print.xpm')).
...
send(X, append, new(B, button(print))),
send(B, label, image(resource(print))),
send(B, help_message, tag, 'Print document'),</PRE>
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