ch17.htm

《Perl 5 Unreleased》

If you use the most current versions of the C++ compiler and make
files, circa 1994 or later, and X11R6, you should have no problems.
In case of problems, please consult the <TT><FONT FACE="Courier">FAQ</FONT></TT>,
<TT><FONT FACE="Courier">INSTALL</FONT></TT>, or <TT><FONT FACE="Courier">README</FONT></TT>
files for your specific system.<P>
<CENTER>
<TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>
<TR VALIGN=TOP><TD ><B>Tip</B></TD></TR>
<TR VALIGN=TOP><TD >
<BLOCKQUOTE>
Keep in mind that your installation may have Perl in a different place than shown here. Instead of <TT><FONT FACE="Courier">/usr/bin/perl</FONT></TT>, you may have to use <TT><FONT FACE="Courier">/usr/local/bin/perl</FONT></TT>.
</BLOCKQUOTE>

</TD></TR>
</TABLE></CENTER>
<P>
<H2><A NAME="DocumentationforPerlTk"><FONT SIZE=5 COLOR=#FF0000>Documentation
for </FONT><TT><FONT SIZE=5 COLOR=#FF0000 FACE="Courier">Perl/Tk</FONT></TT></A>
</H2>
<P>
The <TT><FONT FACE="Courier">make install</FONT></TT> execution
installs the <TT><FONT FACE="Courier">pod</FONT></TT> files for
you in <TT><FONT FACE="Courier">nroff</FONT></TT> format. Check
the <TT><FONT FACE="Courier">perl5/Tk/</FONT></TT> directory for
the file <TT><FONT FACE="Courier">UserGuide.pod</FONT></TT>. This
file is editable and readable by humans. <TT><FONT FACE="Courier">pod</FONT></TT>
files have to be interpreted through a reformatting program such
as <TT><FONT FACE="Courier">pod2man</FONT></TT>, <TT><FONT FACE="Courier">pod2html</FONT></TT>,
or <TT><FONT FACE="Courier">pod2latex</FONT></TT>, all of which
should be in your Perl distribution.
<P>
The following commands provide you with information in HTML files
or in <TT><FONT FACE="Courier">man</FONT></TT> pages:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">pod2man ~khusain/p5/Tk/UserGuide.pod
| nroff -man | more<BR>
pod2html ~khusain/p5/Tk/UserGuide<BR>
perldoc Toplevel.pm</FONT></TT>
</BLOCKQUOTE>
<P>
The most visually pleasing of the three methods is the <TT><FONT FACE="Courier">pod2html</FONT></TT>
method:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">$ <B>pod2html perl5/Tk/Dial.pm<BR>
</B>Creating Dial.pm.html from Dial.pm</FONT></TT>
</BLOCKQUOTE>
<P>
The output of this command is as follows (you can use Mosaic or
Netscape to view the contents of this file):
<BLOCKQUOTE>
<TT><FONT FACE="Courier">&lt;!-- $Id$ --&gt;<BR>
&lt;HTML&gt;&lt;HEAD&gt;<BR>
&lt;CENTER&gt;&lt;TITLE&gt;Dial.pm&lt;/TITLE&gt;<BR>
&lt;/HEAD&gt;<BR>
&lt;BODY&gt;&lt;/CENTER&gt;&lt;p&gt;&lt;hr&gt;<BR>
<BR>
&lt;H1&gt;<BR>
&lt;A NAME=&quot;Dial.pm_name_0&quot;&gt;<BR>
NAME&lt;/A&gt;<BR>
&lt;/H1&gt;<BR>
Dial - an alternative to the scale widget<BR>
&lt;p&gt;&lt;p&gt;&lt;hr&gt;<BR>
<BR>
&lt;H1&gt;<BR>
&lt;A NAME=&quot;Dial.pm_synopsis_0&quot;&gt;<BR>
SYNOPSIS&lt;/A&gt;<BR>
&lt;/H1&gt;<BR>
<BR>
&lt;XMP&gt;<BR>
&nbsp;use Tk::Dial;<BR>
&nbsp;$dial = $top-&gt;Dial(-margin =&gt;&nbsp;&nbsp;20,<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-radius
=&gt;&nbsp;&nbsp;48,<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-min&nbsp;&nbsp;&nbsp;&nbsp;=&gt;&nbsp;&nbsp;&nbsp;0,
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-max&nbsp;&nbsp;&nbsp;&nbsp;=&gt;
100,<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-value&nbsp;&nbsp;=&gt;&nbsp;&nbsp;&nbsp;0,
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-format
=&gt; '%d');<BR>
&nbsp;margin - blank space to leave around dial<BR>
&nbsp;radius - radius of dial<BR>
&nbsp;min, max - range of possible values<BR>
&nbsp;value&nbsp;&nbsp;- current value<BR>
&nbsp;format - printf-style format for displaying format<BR>
<BR>
&lt;/XMP&gt;<BR>
&lt;p&gt;Values shown above are defaults.<BR>
&lt;p&gt;&lt;p&gt;&lt;hr&gt;<BR>
<BR>
&lt;H1&gt;<BR>
&lt;A NAME=&quot;Dial.pm_description_0&quot;&gt;<BR>
DESCRIPTION&lt;/A&gt;<BR>
&lt;/H1&gt;<BR>
A dial looks like a speedometer: a 3/4 circle with a needle indicating
the current value.&nbsp;&nbsp;Below the graphical dial is an entry
that displays the current value, and which can be used to enter
a value by hand. &lt;p&gt;The needle is moved by pressing button
1 in the canvas and dragging. The needle will follow the mouse,
even if the mouse leaves the canvas, which allows for high precision.
Alternatively, the user can enter a value in the entry space and
press Return to set the value; the needle will be set accordingly.
<BR>
&lt;p&gt;&lt;p&gt;&lt;hr&gt;<BR>
<BR>
&lt;H1&gt;<BR>
&lt;A NAME=&quot;Dial.pm_to_0&quot;&gt;<BR>
TO DO&lt;/A&gt;<BR>
&lt;/H1&gt;<BR>
<BR>
&lt;XMP&gt;<BR>
&nbsp;Configure<BR>
&nbsp;Tick marks<BR>
&nbsp;Step size<BR>
<BR>
&lt;/XMP&gt;<BR>
&lt;p&gt;&lt;p&gt;&lt;hr&gt;<BR>
<BR>
&lt;H1&gt;<BR>
&lt;A NAME=&quot;Dial.pm_authors_0&quot;&gt;<BR>
AUTHORS&lt;/A&gt;<BR>
&lt;/H1&gt;<BR>
Roy Johnson, &lt;A HREF=&quot;MAILTO:[e-mail]&quot;&gt;[e-mail]&lt;/A&gt;
<BR>
&lt;p&gt;Based on a similar widget in XV, a program by John Bradley,
<BR>
&lt;A HREF=&quot;MAILTO:[e-mail]&quot;&gt;[e-mail]&lt;/A&gt;
<BR>
&lt;p&gt;&lt;p&gt;&lt;hr&gt;<BR>
<BR>
&lt;H1&gt;<BR>
&lt;A NAME=&quot;Dial.pm_history_0&quot;&gt;<BR>
HISTORY &lt;/A&gt;<BR>
&lt;/H1&gt;<BR>
<BR>
&lt;XMP&gt;<BR>
<BR>
August 1995: Released for critique by pTk mailing list<BR>
<BR>
&lt;/XMP&gt;<BR>
&lt;p&gt;<BR>
&lt;/BODY&gt;<BR>
&lt;/HTML&gt;</FONT></TT>
</BLOCKQUOTE>
<P>
Also in the <TT><FONT FACE="Courier">Tk-b9.01/doc</FONT></TT>
directory are some <TT><FONT FACE="Courier">.ht</FONT></TT> files
which are copyrighted HTML pages of the documentation for the
package. 
<H2><A NAME="WritingScriptsinPerlTk"><FONT SIZE=5 COLOR=#FF0000>Writing
Scripts in </FONT><TT><FONT SIZE=5 COLOR=#FF0000 FACE="Courier">Perl/Tk</FONT></TT></A>
</H2>
<P>
The idea behind writing the <TT><FONT FACE="Courier">Perl/Tk</FONT></TT>
script using the modules for the package is to make life easier.
The scripts have to include the <TT><FONT FACE="Courier">Tk</FONT></TT>
package with the <TT><FONT FACE="Courier">use Tk;</FONT></TT>
statement. You might want to consider using the warning switch
(<TT><FONT FACE="Courier">-w</FONT></TT>) and, if you are paranoid,
use the <TT><FONT FACE="Courier">use strict;</FONT></TT> statement
to do extra syntax checking.
<P>
Look at the simple &quot;Hello, world&quot; script shown in Listing
17.1.
<HR>
<BLOCKQUOTE>
<B>Listing 17.1. A simple &quot;Hello, world&quot; script.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT><FONT FACE="Courier">&nbsp;1&nbsp;&nbsp;#!/usr/bin/perl -w
<BR>
&nbsp;2&nbsp;&nbsp;#<BR>
&nbsp;3&nbsp;&nbsp;# Simple Tk script to create a button that
prints &quot;Hello, world&quot;.<BR>
&nbsp;4&nbsp;&nbsp;#<BR>
&nbsp;5&nbsp;&nbsp;use Tk;<BR>
&nbsp;6&nbsp;&nbsp;$mw = MainWindow-&gt;new;<BR>
&nbsp;7&nbsp;&nbsp;$hello = $mw-&gt;Button(-text =&gt; 'Hello,
world',<BR>
&nbsp;&nbsp;&nbsp;&nbsp;<FONT FACE="ZAPFDINGBATS">&Acirc;</FONT>
-command =&gt; sub {print STDOUT &quot;Hello, world\n&quot;; });
<BR>
&nbsp;8&nbsp;&nbsp;$greet = $mw-&gt;Button(-text =&gt; 'Greetings',
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;<FONT FACE="ZAPFDINGBATS">&Acirc;</FONT>
-command =&gt; sub {print STDOUT &quot;Greetings\n&quot;; exit;});
<BR>
&nbsp;9&nbsp;&nbsp;$hello-&gt;pack;<BR>
10 $greet-&gt;pack(-side =&gt; &quot;left&quot;);<BR>
11 MainLoop;</FONT></TT>
</BLOCKQUOTE>
<HR>
<P>
The first line in the file starts Perl with the <TT><FONT FACE="Courier">-w</FONT></TT>
switch for warnings to be issued, if necessary. Line 5 imports
the <TT><FONT FACE="Courier">Tk</FONT></TT> objects into the application.
The statement in line 6 creates the main window. The &quot;Hello,
world&quot; and Greetings buttons are created in lines 7 and 8.
In line 9, the Hello button is added to the main window. In line
10, the Greetings button is <TT><FONT FACE="Courier">pack</FONT></TT>-ed
into the main window on the left side of the Hello button. (I
cover <TT><FONT FACE="Courier">pack</FONT></TT>-ing later throughout
this chapter.) Line 11 starts the main user interface loop for
this application. The output is shown in Figure 17.1.
<P>
<A HREF="f17-1.gif" tppabs="http://www.mcp.com/815097600/0-672/0-672-30891-6/f17-1.gif"><B>Figure 17.1 :</B><I>Sample &quot;Hello, world&quot; application.</I></A>
<P>
The <TT><FONT FACE="Courier">MainLoop;</FONT></TT> statement is
the main widget event handler loop and is required in all <TT><FONT FACE="Courier">Perl/Tk</FONT></TT>
scripts. This event handler statement is usually near the end
of the <TT><FONT FACE="Courier">main</FONT></TT> procedure after
the widgets have been created and are ready to be displayed.
<P>
In Listing 17.1, note that the Greet button defines an anonymous
function (at line 8) with a call to the <TT><FONT FACE="Courier">exit</FONT></TT>
function. In line 7, the <TT><FONT FACE="Courier">hello world</FONT></TT>
function does not call the <TT><FONT FACE="Courier">exit</FONT></TT>
function.
<P>
The objects in this application are added one object at a time
in a hierarchical order. This <BR>
involves the use of the <TT><FONT FACE="Courier">-&gt; </FONT></TT>infix
dereference operator; for example, the <TT><FONT FACE="Courier">$mw-&gt;Button(...)</FONT></TT>
call forces the button to be created with the <TT><FONT FACE="Courier">$mw</FONT></TT>
object as the parent. Almost all objects and parameters in calls
to <TT><FONT FACE="Courier">Perl/Tk</FONT></TT> routines are passed
by reference.
<P>
Please note the use of the <TT><FONT FACE="Courier">=&gt;</FONT></TT>
operator, which is simply a synonym for the comma operator. The
program in Listing 17.1 could be rewritten as shown in Listings
17.2 and 17.3.
<HR>
<BLOCKQUOTE>
<B>Listing 17.2. The &quot;Hello, world&quot; application using
commas.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT><FONT FACE="Courier">&nbsp;1 #!/usr/bin/perl -w<BR>
&nbsp;2 #<BR>
&nbsp;3 # Using commas instead of =&gt;.<BR>
&nbsp;4 #<BR>
&nbsp;5 <BR>
&nbsp;6 use Tk;<BR>
&nbsp;7 $mw = MainWindow-&gt;new;<BR>
&nbsp;8 $hello = $mw-&gt;Button(-text , 'Hello, world',<BR>
&nbsp;&nbsp;&nbsp;<FONT FACE="ZAPFDINGBATS">&Acirc;</FONT>-command , sub {print
STDOUT &quot;Hello, world\n&quot;; });<BR>
&nbsp;9 $greet = $mw-&gt;Button(-text , 'Greetings', <BR>
&nbsp;&nbsp;&nbsp;<FONT FACE="ZAPFDINGBATS">&Acirc;</FONT>-command , sub {print
STDOUT &quot;Greetings\n&quot;; exit;});<BR>
10 $hello-&gt;pack;<BR>
11 $greet-&gt;pack(-side , &quot;left&quot;);<BR>
12 MainLoop;</FONT></TT>
</BLOCKQUOTE>
<HR>
<HR>
<BLOCKQUOTE>
<B>Listing 17.3. The &quot;Hello, world&quot; application using
hashes.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT><FONT FACE="Courier">&nbsp;1 #!/usr/bin/perl -w<BR>
&nbsp;2 #<BR>
&nbsp;3 # Using Hashes instead of dereferencing using -&gt;<BR>
&nbsp;4 #<BR>
&nbsp;5 <BR>
&nbsp;6 use Tk;<BR>
&nbsp;7 $mw = MainWindow-&gt;new;<BR>