UserGuide(3pm) User Contributed Perl Documentation UserGuide(3pm)
NAME
Tk::UserGuide - Writing Tk applications in Perl 5
DESCRIPTION
This document is for beginners. It assumes you know some Perl, and have
it and Tk running. If you are not currently reading this document
courtesy of the widget demonstration program, please be sure to run
widget, as it will show you the various widget types supported by Tk and
how to use them. widget should be installed in your default path, so
type widget at a command prompt.
Here are links to other novice tutorials:
<http://www.lehigh.edu/~sol0/ptk/tpj1.html>
<http://www.lehigh.edu/~sol0/ptk/perlmonth01/pm1.html>
Mastering Perl/Tk is the definitive book on Perl/Tk:
<http://www.oreilly.com/catalog/mastperltk>
Some Background
Tk GUI programming is event-driven. (This may already be familiar to
you.) In event-driven programs, the main GUI loop is outside of the
user program and inside the GUI library. This loop - initiated by
calling MainLoop - watches all events of interest and activates the
correct handler procedures to handle these events. Some of these
handler procedures may be user-supplied; others will be part of the
library.
For a programmer, this means that you're not watching what is happening;
instead, you are requested by the toolkit to perform actions whenever
necessary. So, you're not watching for 'raise window / close window /
redraw window' requests, but you tell the toolkit which routine will
handle such cases, and the toolkit will call the procedures when
required. These procedures are known as callbacks, and some of them you
write yourself.
First Requirements
Perl programs that use Tk need to include "use Tk". A program should
also use "use strict" and the -w switch to ensure the program is working
without common errors.
Any Perl/Tk application starts by creating the Tk MainWindow. You then
create items inside the MainWindow, and/or create new windows called
Toplevels that also contain child items, before starting the MainLoop,
which is the last logical statment in your program. You can also create
more items and windows while you're running, using callbacks. Items are
only shown on the display after they have been arranged by a geometry
manager like pack; more information on this later. MainLoop starts the
GUI and handle all events. That's all there is to it! A trivial one-
window example is shown below:
#!/usr/bin/perl -w
use Tk;
use strict;
my $mw = MainWindow->new;
$mw->Label(-text => 'Hello, world!')->pack;
$mw->Button(
-text => 'Quit',
-command => sub { exit },
)->pack;
MainLoop;
Please run this example. It shows you two widget types, a Label and a
Button, and how they are packed. When clicked, the Button widget invokes
the callback specified by the "-command" option. Finally, note the
typical Tk style using "-option" => "value" pairs.
Widget creation
Tk windows and widgets are hierarchical, i.e. one window includes one or
more other windows. You create the first Tk window using
"MainWindow->new". This returns a window handle, assigned to $mw in the
example above. Keep track of the main handle, commonly called a widget
reference.
You can use any Tk handle to create child widgets within the window (or
widget). This is done by calling the Tk constructor method on the
variable. In the example above, the "Label" method called from $mw
creates a Label widget inside the MainWindow. In the constructor call,
you can specify various options; you can later add or change options for
any widget using the configure method, which takes the same parameters
as the constructor. The one exception to the hierarchical structure is
the Toplevel constructor, which creates a new outermost window.
After you create any widget (other than the MainWindow or Toplevels, you
must render it by calling pack. (This is not entirely true; more
later)). If you do not need to refer to the widget after construction
and packing, call pack off the constructor results, as shown for the
Label and Button in the example above. Note that the result of the
compound call is the result of pack, which is a valid Tk handle.
Windows and widgets are deleted by calling destroy on them; this will
delete and un-draw the widget and all its children.
Standard Tk widgets
Here is an itemize of the standard Tk widget set.
Button
Canvas
Checkbutton
Entry
Frame
Label
Labelframe
Listbox
Menu
Menubutton
Message
Panedwindow
Radiobutton
Scale
Scrollbar
Spinbox
Text
Toplevel
Perl/Tk provides an equal number of new widgets, above and beyond this
core set.
Adjuster
Balloon
BrowseEntry
ColorEditor
Dialog
DialogBox
DirTree
ErrorDialog
FBox
FileSelect
HList
LabEntry
LabFrame
NoteBook
Optionmenu
Pane
ProgressBar
ROText
Table
TextUndo
Tiler
TList
Tree
Variables and callback routines
Most graphical interfaces are used to set up a set of values and
conditions, and then perform the appropriate action. The Tk toolkit is
different from your average text-based prompting or menu driven system
in that you do not collect settings yourself, and decide on an action
based on an input code; instead, you leave these values to your toolkit
and only get them when the action is performed.
So, where a traditional text-based system would look like this:
#!/usr/bin/perl -w
use strict;
print "Please type a font name\n";
my $font = <>; chomp $font;
# Validate font
print "Please type a file name\n";
my $filename = <>; chomp $filename;
# Validate filename
print "Type <1> to fax, <2> to print\n";
my $option = <>; chomp $option;
if ($option eq 1) {
print "Faxing $filename in font $font\n";
} elsif ($option eq 2) {
print "Now sending $filename to printer in font $font\n";
}
The slightly larger example below shows how to do this in Tk. Note the
use of callbacks. Note, also, that Tk handles the values, and the
subroutine uses the method get to get at the values. If a user changes
his mind and wants to change the font again, the application never
notices; it's all handled by Tk.
#!/usr/bin/perl -w
use Tk;
use strict;
my $mw = MainWindow->new;
$mw->Label(-text => 'File Name')->pack;
my $filename = $mw->Entry(-width => 20);
$filename->pack;
$mw->Label(-text => 'Font Name')->pack;
my $font = $mw->Entry(-width => 10);
$font->pack;
$mw->Button(
-text => 'Fax',
-command => sub{do_fax($filename, $font)}
)->pack;
$mw->Button(
-text => 'Print',
-command => sub{do_print($filename, $font)}
)->pack;
MainLoop;
sub do_fax {
my ($file, $font) = @_;
my $file_val = $file->get;
my $font_val = $font->get;
print "Now faxing $file_val in font $font_val\n";
}
sub do_print {
my ($file, $font) = @_;
my $file_val = $file->get;
my $font_val = $font->get;
print "Sending file $file_val to printer in font $font_val\n";
}
The packer - grouping with Frame widgets
In the examples above, you must have noticed the pack calls. This is
one of the more complicated parts of Tk. The basic idea is that any
window or widget should be subject to a Tk geometry manager; the packer
is one of the placement managers, and grid is another.
The actions of the packer are rather simple: when applied to a widget,
the packer positions that widget on the indicated position within the
remaining space in its parent. By default, the position is on top; this
means the next items will be put below. You can also specify the left,
right, or bottom positions. Specify position using -side => 'right'.
Additional packing parameters specify the behavior of the widget when
there is some space left in the Frame or when the window size is
increased. If widgets should maintain a fixed size, specify nothing;
this is the default. For widgets that you want to fill up the current
horizontal and/or vertical space, specify -fill => 'x', 'y', or 'both';
for widgets that should grow, specify -expand => 1. These parameters
are not shown in the example below; see the widget demonstration.
If you want to group some items within a window that have a different
packing order than others, you can include them in a Frame. This is a
do-nothing window type that is meant for packing or filling (and to play
games with borders and colors).
The example below shows the use of pack and Frames:
#!/usr/bin/perl -w
use Tk;
use strict;
# Take top and the bottom - now implicit top is in the middle
my $mw = MainWindow->new;
$mw->title( 'The MainWindow' );
$mw->Label(-text => 'At the top (default)')->pack;
$mw->Label(-text => 'At the bottom')->pack(-side => 'bottom');
$mw->Label(-text => 'The middle remains')->pack;
# Since left and right are taken, bottom will not work...
my $top1 = $mw->Toplevel;
$top1->title( 'Toplevel 1' );
$top1->Label(-text => 'Left')->pack(-side => 'left');
$top1->Label(-text => 'Right')->pack(-side => 'right');
$top1->Label(-text => '?Bottom?')->pack(-side => 'bottom');
# But when you use Frames, things work quite alright
my $top2 = $mw->Toplevel;
$top2->title( 'Toplevel 2' );
my $frame = $top2->Frame;
$frame->pack;
$frame->Label(-text => 'Left2')->pack(-side => 'left');
$frame->Label(-text => 'Right2')->pack(-side => 'right');
$top2->Label(-text => 'Bottom2')->pack(-side => 'bottom');
MainLoop;
More than one window
Most real applications require more than one window. As you just saw,
you can create more outermost windows by using a Toplevel widget. Each
window is independent; destroying a Toplevel window does not affect the
others as long as they are not a child of the closed Toplevel. However,
exiting the MainWindow will destroy all remaining Toplevel widgets and
end the application. The example below shows a trivial three-window
application:
#!/usr/bin/perl -w
use Tk;
use strict;
my $mw = MainWindow->new;
fill_window($mw, 'Main');
my $top1 = $mw->Toplevel;
fill_window($top1, 'First top-level');
my $top2 = $mw->Toplevel;
fill_window($top2, 'Second top-level');
MainLoop;
sub fill_window {
my ($window, $header) = @_;
$window->Label(-text => $header)->pack;
$window->Button(
-text => 'close',
-command => [$window => 'destroy']
)->pack(-side => 'left');
$window->Button(
-text => 'exit',
-command => [$mw => 'destroy']
)->pack(-side => 'right');
}
More callbacks
So far, all callback routines shown called a user procedure. You can
also have a callback routine call another Tk routine. This is the way
that scroll bars are implemented: scroll-bars can call a Tk item or a
user procedure, whenever their position has changed. The Tk item that
has a scrollbar attached calls the scrollbar when its size or offset has
changed. In this way, the items are linked. You can still ask a
scrollbar's position, or set it by hand - but the defaults will be taken
care of.
The example below shows a Listbox with a scroll bar. Moving the
scrollbar moves the Listbox. Scanning a Listbox (dragging an item with
the left mouse button) moves the scrollbar.
#!/usr/bin/perl -w
use Tk;
use strict;
my $mw = MainWindow->new;
my $box = $mw->Listbox(
-relief => 'sunken',
-height => 5,
-setgrid => 1,
);
my @items = qw(One Two Three Four Five Six Seven
Eight Nine Ten Eleven Twelve);
foreach (@items) {
$box->insert('end', $_);
}
my $scroll = $mw->Scrollbar(-command => ['yview', $box]);
$box->configure(-yscrollcommand => ['set', $scroll]);
$box->pack(-side => 'left', -fill => 'both', -expand => 1);
$scroll->pack(-side => 'right', -fill => 'y');
MainLoop;
Note that there's a convenience method Scrolled which helps constructing
widgets with automatically managed scrollbars.
Canvases and tags
One of the most powerful widgets in Tk is the Canvas window. In a
Canvas window, you can draw simple graphics and include other widgets.
The Canvas area may be larger than the visible window, and may then be
scrolled. Any item you draw on the canvas has its own id, and may
optionally have one or more tags. You may refer to any item by its id,
and may refer to any group of items by a common tag; you can move,
delete, or change groups of items using these tags, and you can bind
actions to tags. For a properly designed (often structured) Canvas, you
can specify powerful actions quite simply.
In the example below, actions are bound to circles (single click) and
blue items (double-click); obviously, this can be extended to any tag or
group of tags.
#!/usr/bin/perl -w
use Tk;
use strict;
# Create B<MainWindow> and canvas
my $mw = MainWindow->new;
my $canvas = $mw->Canvas;
$canvas->pack(-expand => 1, -fill => 'both');
# Create various items
create_item($canvas, 1, 1, 'circle', 'blue', 'Jane');
create_item($canvas, 4, 4, 'circle', 'red', 'Peter');
create_item($canvas, 4, 1, 'square', 'blue', 'James');
create_item($canvas, 1, 4, 'square', 'red', 'Patricia');
# Single-clicking with left on a 'circle' item invokes a procedure
$canvas->bind('circle', '<1>' => sub {handle_circle($canvas)});
# Double-clicking with left on a 'blue' item invokes a procedure
$canvas->bind('blue', '<Double-1>' => sub {handle_blue($canvas)});
MainLoop;
# Create an item; use parameters as tags (this is not a default!)
sub create_item {
my ($can, $x, $y, $form, $color, $name) = @_;
my $x2 = $x + 1;
my $y2 = $y + 1;
my $kind;
$kind = 'oval' if ($form eq 'circle');
$kind = 'rectangle' if ($form eq 'square');
$can->create(
($kind, "$x" . 'c', "$y" . 'c',
"$x2" . 'c', "$y2" . 'c'),
-tags => [$form, $color, $name],
-fill => $color);
}
# This gets the real name (not current, blue/red, square/circle)
# Note: you'll want to return a list in realistic situations...
sub get_name {
my ($can) = @_;
my $item = $can->find('withtag', 'current');
my @taglist = $can->gettags($item);
my $name;
foreach (@taglist) {
next if ($_ eq 'current');
next if ($_ eq 'red' or $_ eq 'blue');
next if ($_ eq 'square' or $_ eq 'circle');
$name = $_;
last;
}
return $name;
}
sub handle_circle {
my ($can) = @_;
my $name = get_name($can);
print "Action on circle $name...\n";
}
sub handle_blue {
my ($can) = @_;
my $name = get_name($can);
print "Action on blue item $name...\n";
}
Perl/Tk and Unicode
Perl/Tk follows Perl's model of handling Unicode. That is, if a string
is correctly flagged as a "character" string in the sense like described
in "TERMINOLOGY" in Encode, then Perl/Tk will very probably display and
handle this string correctly.
Note that every variable which is passed somehow into a Perl/Tk method
will be implicitely changed into an internally utf8-flagged variable.
Semantically nothing changes, as the series of codepoints stays the
same, but things will change when variables with high-bit iso-8859-1
characters will be passed to the "outer" world. In this case you have to
explicitly mark the encoding of your output stream if using IO, or
encode the variables using Encode for other style of communication.
This is the theory, now some examples.
If you use non-iso-8859-1 characters in the source code, then use either
the "use utf8;" or "use encoding 'encodingname'" pragma:
use utf8;
use Tk;
my $x = "some characters using utf8 encoding";
tkinit->Label(-text => $x)->pack;
MainLoop;
For data that comes from a file you have to specify the encoding unless
it's encoded as ascii or iso-8559-1:
use Tk;
open my $FH, "<:encoding(utf-8)", "filename" or die $!;
# or for utf-16 data: open my $FH, "<:encoding(utf-16)", "filename" or die $!;
my $data = <$FH>;
tkinit->Label(-text => $data)->pack;
MainLoop;
Likewise, the encoding must be specified for all data which is read from
Tk widgets and that shall be output into a file. For the output, the
encoding should be always specified, even if it is iso-8859-1:
use Tk;
$mw = tkinit;
$mw->Entry(-textvariable => \$input)->pack;
$mw->Button(
-text => "Write to file",
-command => sub {
open my $FH, ">:encoding(iso-8859-1)", "filename" or die $!;
print $FH $input;
},
)->pack;
MainLoop;
Note that Tk is Unicode-capable. So you need to be prepared that the
user has the appropriate input methods activated to enter non-ascii
characters. If an output encoding is used which does not cover the whole
of Unicode codepoints then a warning will be issued when writing the
file, like this:
"\x{20ac}" does not map to iso-8859-1 at /usr/local/lib/perl5/site_perl/5.8.8/mach/Tk.pm line 250.
Also, the same hexadecimal notation will be used as replacements for the
unhandled characters.
Handling encoding in I/O is pretty simple using the "encoding" PerlIO
layer, as described above. In other cases, such as when dealing with
databases, encoding the data usually has to be done manually, unless the
database driver has some means for automatically do this for you. So
when working with a MySQL database, one could use:
use Tk;
use DBI;
use Encode qw(encode);
$mw = tkinit;
$mw->Entry(-textvariable => \$input)->pack;
$mw->Button(
-text => "Write to database",
-command => sub {
my $dbh = DBI->connect("dbi:mysql:test", "root", "") or die;
my $encoded_input = encode("iso-8859-1", $input);
$dbh->do("INSERT INTO testtable VALUES (?)", undef, $encoded_input) or die;
},
)->pack;
MainLoop;
Unfortunately, there are still places in Perl ignorant of Unicode. One
of these places are filenames. Consequently, the file selectors in
Perl/Tk do not handle encoding of filenames properly. Currently they
suppose that filenames are in iso-8859-1 encoding, at least on Unix
systems. As soon as Perl has a concept of filename encodings, then
Perl/Tk will also implement such schemes.
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