1UserGuide(3)          User Contributed Perl Documentation         UserGuide(3)
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4

NAME

6       Tk::UserGuide - Writing Tk applications in Perl 5
7

DESCRIPTION

9       This document is for beginners.  It assumes you know some Perl, and
10       have it and Tk running.  If you are not currently reading this document
11       courtesy of the widget demonstration program, please be sure to run
12       widget, as it will show you the various widget types supported by Tk
13       and how to use them. widget should be installed in your default path,
14       so type widget at a command prompt.
15
16       Here are links to other novice tutorials:
17
18       <http://www.lehigh.edu/~sol0/ptk/tpj1.html>
19       <http://www.lehigh.edu/~sol0/ptk/perlmonth01/pm1.html>
20
21       Mastering Perl/Tk is the definitive book on Perl/Tk:
22
23       <http://www.oreilly.com/catalog/mastperltk>
24

Some Background

26       Tk GUI programming is event-driven.  (This may already be familiar to
27       you.)  In event-driven programs, the main GUI loop is outside of the
28       user program and inside the GUI library.  This loop - initiated by
29       calling MainLoop - watches all events of interest and activates the
30       correct handler procedures to handle these events.  Some of these
31       handler procedures may be user-supplied; others will be part of the
32       library.
33
34       For a programmer, this means that you're not watching what is
35       happening; instead, you are requested by the toolkit to perform actions
36       whenever necessary.  So, you're not watching for 'raise window / close
37       window / redraw window' requests, but you tell the toolkit which
38       routine will handle such cases, and the toolkit will call the
39       procedures when required. These procedures are known as callbacks, and
40       some of them you write yourself.
41

First Requirements

43       Perl programs that use Tk need to include "use Tk".  A program should
44       also use "use strict" and the -w switch to ensure the program is
45       working without common errors.
46
47       Any Perl/Tk application starts by creating the Tk MainWindow.  You then
48       create items inside the MainWindow, and/or create new windows called
49       Toplevels that also contain child items, before starting the MainLoop,
50       which is the last logical statment in your program. You can also create
51       more items and windows while you're running, using callbacks.  Items
52       are only shown on the display after they have been arranged by a
53       geometry manager like pack; more information on this later.  MainLoop
54       starts the GUI and handle all events.  That's all there is to it!  A
55       trivial one-window example is shown below:
56
57           #!/usr/bin/perl -w
58           use Tk;
59           use strict;
60
61           my $mw = MainWindow->new;
62           $mw->Label(-text => 'Hello, world!')->pack;
63           $mw->Button(
64               -text    => 'Quit',
65               -command => sub { exit },
66           )->pack;
67           MainLoop;
68
69       Please run this example.  It shows you two widget types, a Label and a
70       Button, and how they are packed. When clicked, the Button widget
71       invokes the callback specified by the "-command" option.  Finally, note
72       the typical Tk style using "-option" => "value" pairs.
73

Widget creation

75       Tk windows and widgets are hierarchical, i.e. one window includes one
76       or more other windows.  You create the first Tk window using
77       "MainWindow->new".  This returns a window handle, assigned to $mw in
78       the example above.  Keep track of the main handle, commonly called a
79       widget reference.
80
81       You can use any Tk handle to create child widgets within the window (or
82       widget).  This is done by calling the Tk constructor method on the
83       variable.  In the example above, the "Label" method called from $mw
84       creates a Label widget inside the MainWindow.  In the constructor call,
85       you can specify various options; you can later add or change options
86       for any widget using the configure method, which takes the same
87       parameters as the constructor.  The one exception to the hierarchical
88       structure is the Toplevel constructor, which creates a new outermost
89       window.
90
91       After you create any widget (other than the MainWindow or Toplevels,
92       you must render it by calling pack.  (This is not entirely true; more
93       later)).  If you do not need to refer to the widget after construction
94       and packing, call pack off the constructor results, as shown for the
95       Label and Button in the example above.  Note that the result of the
96       compound call is the result of pack, which is a valid Tk handle.
97
98       Windows and widgets are deleted by calling destroy on them; this will
99       delete and un-draw the widget and all its children.
100

Standard Tk widgets

102       Here is an itemize of the standard Tk widget set.
103
104       Button
105       Canvas
106       Checkbutton
107       Entry
108       Frame
109       Label
110       Labelframe
111       Listbox
112       Menu
113       Menubutton
114       Message
115       Panedwindow
116       Radiobutton
117       Scale
118       Scrollbar
119       Spinbox
120       Text
121       Toplevel
122
123       Perl/Tk provides an equal number of new widgets, above and beyond this
124       core set.
125
126       Adjuster
127       Balloon
128       BrowseEntry
129       ColorEditor
130       Dialog
131       DialogBox
132       DirTree
133       ErrorDialog
134       FBox
135       FileSelect
136       HList
137       LabEntry
138       LabFrame
139       NoteBook
140       Optionmenu
141       Pane
142       ProgressBar
143       ROText
144       Table
145       TextUndo
146       Tiler
147       TList
148       Tree
149

Variables and callback routines

151       Most graphical interfaces are used to set up a set of values and
152       conditions, and then perform the appropriate action.  The Tk toolkit is
153       different from your average text-based prompting or menu driven system
154       in that you do not collect settings yourself, and decide on an action
155       based on an input code; instead, you leave these values to your toolkit
156       and only get them when the action is performed.
157
158       So, where a traditional text-based system would look like this:
159
160           #!/usr/bin/perl -w
161           use strict;
162
163           print "Please type a font name\n";
164           my $font = <>; chomp $font;
165           # Validate font
166
167           print "Please type a file name\n";
168           my $filename = <>; chomp $filename;
169           # Validate filename
170
171           print "Type <1> to fax, <2> to print\n";
172           my $option = <>; chomp $option;
173           if ($option eq 1) {
174               print "Faxing $filename in font $font\n";
175           } elsif ($option eq 2) {
176               print "Now sending $filename to printer in font $font\n";
177           }
178
179       The slightly larger example below shows how to do this in Tk.  Note the
180       use of callbacks.  Note, also, that Tk handles the values, and the
181       subroutine uses the method get to get at the values.  If a user changes
182       his mind and wants to change the font again, the application never
183       notices; it's all handled by Tk.
184
185           #!/usr/bin/perl -w
186           use Tk;
187           use strict;
188
189           my $mw = MainWindow->new;
190
191           $mw->Label(-text => 'File Name')->pack;
192           my $filename = $mw->Entry(-width => 20);
193           $filename->pack;
194
195           $mw->Label(-text => 'Font Name')->pack;
196           my $font = $mw->Entry(-width => 10);
197           $font->pack;
198
199           $mw->Button(
200               -text => 'Fax',
201               -command => sub{do_fax($filename, $font)}
202           )->pack;
203
204           $mw->Button(
205               -text => 'Print',
206               -command => sub{do_print($filename, $font)}
207           )->pack;
208
209           MainLoop;
210
211           sub do_fax {
212               my ($file, $font) = @_;
213               my $file_val = $file->get;
214               my $font_val = $font->get;
215               print "Now faxing $file_val in font $font_val\n";
216           }
217
218           sub do_print {
219               my ($file, $font) = @_;
220               my $file_val = $file->get;
221               my $font_val = $font->get;
222               print "Sending file $file_val to printer in font $font_val\n";
223           }
224

The packer - grouping with Frame widgets

226       In the examples above, you must have noticed the pack calls.  This is
227       one of the more complicated parts of Tk.  The basic idea is that any
228       window or widget should be subject to a Tk geometry manager; the packer
229       is one of the placement managers, and grid is another.
230
231       The actions of the packer are rather simple: when applied to a widget,
232       the packer positions that widget on the indicated position within the
233       remaining space in its parent.  By default, the position is on top;
234       this means the next items will be put below.  You can also specify the
235       left, right, or bottom positions.  Specify position using -side =>
236       'right'.
237
238       Additional packing parameters specify the behavior of the widget when
239       there is some space left in the Frame or when the window size is
240       increased.  If widgets should maintain a fixed size, specify nothing;
241       this is the default.  For widgets that you want to fill up the current
242       horizontal and/or vertical space, specify -fill => 'x', 'y', or 'both';
243       for widgets that should grow, specify -expand => 1.  These parameters
244       are not shown in the example below; see the widget demonstration.
245
246       If you want to group some items within a window that have a different
247       packing order than others, you can include them in a Frame.  This is a
248       do-nothing window type that is meant for packing or filling (and to
249       play games with borders and colors).
250
251       The example below shows the use of pack and Frames:
252
253           #!/usr/bin/perl -w
254           use Tk;
255           use strict;
256
257           # Take top and the bottom - now implicit top is in the middle
258           my $mw = MainWindow->new;
259           $mw->title( 'The MainWindow' );
260           $mw->Label(-text => 'At the top (default)')->pack;
261           $mw->Label(-text => 'At the bottom')->pack(-side => 'bottom');
262           $mw->Label(-text => 'The middle remains')->pack;
263
264           # Since left and right are taken, bottom will not work...
265           my $top1 = $mw->Toplevel;
266           $top1->title( 'Toplevel 1' );
267           $top1->Label(-text => 'Left')->pack(-side => 'left');
268           $top1->Label(-text => 'Right')->pack(-side => 'right');
269           $top1->Label(-text => '?Bottom?')->pack(-side => 'bottom');
270
271           # But when you use Frames, things work quite alright
272           my $top2 = $mw->Toplevel;
273           $top2->title( 'Toplevel 2' );
274           my $frame = $top2->Frame;
275           $frame->pack;
276           $frame->Label(-text => 'Left2')->pack(-side => 'left');
277           $frame->Label(-text => 'Right2')->pack(-side => 'right');
278           $top2->Label(-text => 'Bottom2')->pack(-side => 'bottom');
279
280           MainLoop;
281

More than one window

283       Most real applications require more than one window.  As you just saw,
284       you can create more outermost windows by using a Toplevel widget.  Each
285       window is independent; destroying a Toplevel window does not affect the
286       others as long as they are not a child of the closed Toplevel.
287       However, exiting the MainWindow will destroy all remaining Toplevel
288       widgets and end the application.  The example below shows a trivial
289       three-window application:
290
291           #!/usr/bin/perl -w
292           use Tk;
293           use strict;
294
295           my $mw = MainWindow->new;
296           fill_window($mw, 'Main');
297           my $top1 = $mw->Toplevel;
298           fill_window($top1, 'First top-level');
299           my $top2 = $mw->Toplevel;
300           fill_window($top2, 'Second top-level');
301           MainLoop;
302
303           sub fill_window {
304               my ($window, $header) = @_;
305               $window->Label(-text => $header)->pack;
306               $window->Button(
307                   -text    => 'close',
308                   -command => [$window => 'destroy']
309               )->pack(-side => 'left');
310               $window->Button(
311                   -text    => 'exit',
312                   -command => [$mw => 'destroy']
313               )->pack(-side => 'right');
314           }
315

More callbacks

317       So far, all callback routines shown called a user procedure.  You can
318       also have a callback routine call another Tk routine.  This is the way
319       that scroll bars are implemented: scroll-bars can call a Tk item or a
320       user procedure, whenever their position has changed.  The Tk item that
321       has a scrollbar attached calls the scrollbar when its size or offset
322       has changed.  In this way, the items are linked.  You can still ask a
323       scrollbar's position, or set it by hand - but the defaults will be
324       taken care of.
325
326       The example below shows a Listbox with a scroll bar.  Moving the
327       scrollbar moves the Listbox.  Scanning a Listbox (dragging an item with
328       the left mouse button) moves the scrollbar.
329
330            #!/usr/bin/perl -w
331            use Tk;
332            use strict;
333
334            my $mw = MainWindow->new;
335            my $box = $mw->Listbox(
336                -relief => 'sunken',
337                -height  => 5,
338                -setgrid => 1,
339           );
340           my @items = qw(One Two Three Four Five Six Seven
341                          Eight Nine Ten Eleven Twelve);
342           foreach (@items) {
343              $box->insert('end', $_);
344           }
345           my $scroll = $mw->Scrollbar(-command => ['yview', $box]);
346           $box->configure(-yscrollcommand => ['set', $scroll]);
347           $box->pack(-side => 'left', -fill => 'both', -expand => 1);
348           $scroll->pack(-side => 'right', -fill => 'y');
349
350           MainLoop;
351
352       Note that there's a convenience method Scrolled which helps
353       constructing widgets with automatically managed scrollbars.
354

Canvases and tags

356       One of the most powerful widgets in Tk is the Canvas window.  In a
357       Canvas window, you can draw simple graphics and include other widgets.
358       The Canvas area may be larger than the visible window, and may then be
359       scrolled.  Any item you draw on the canvas has its own id, and may
360       optionally have one or more tags.  You may refer to any item by its id,
361       and may refer to any group of items by a common tag; you can move,
362       delete, or change groups of items using these tags, and you can bind
363       actions to tags.  For a properly designed (often structured) Canvas,
364       you can specify powerful actions quite simply.
365
366       In the example below, actions are bound to circles (single click) and
367       blue items (double-click); obviously, this can be extended to any tag
368       or group of tags.
369
370           #!/usr/bin/perl -w
371           use Tk;
372           use strict;
373
374           # Create B<MainWindow> and canvas
375           my $mw = MainWindow->new;
376           my $canvas = $mw->Canvas;
377           $canvas->pack(-expand => 1, -fill => 'both');
378
379           # Create various items
380           create_item($canvas, 1, 1, 'circle', 'blue', 'Jane');
381           create_item($canvas, 4, 4, 'circle', 'red', 'Peter');
382           create_item($canvas, 4, 1, 'square', 'blue', 'James');
383           create_item($canvas, 1, 4, 'square', 'red', 'Patricia');
384
385           # Single-clicking with left on a 'circle' item invokes a procedure
386           $canvas->bind('circle', '<1>' => sub {handle_circle($canvas)});
387           # Double-clicking with left on a 'blue' item invokes a procedure
388           $canvas->bind('blue', '<Double-1>' => sub {handle_blue($canvas)});
389           MainLoop;
390
391           # Create an item; use parameters as tags (this is not a default!)
392           sub create_item {
393               my ($can, $x, $y, $form, $color, $name) = @_;
394
395               my $x2 = $x + 1;
396               my $y2 = $y + 1;
397               my $kind;
398               $kind = 'oval' if ($form eq 'circle');
399               $kind = 'rectangle' if ($form eq 'square');
400               $can->create(
401                   ($kind, "$x" . 'c', "$y" . 'c',
402                   "$x2" . 'c', "$y2" . 'c'),
403                   -tags => [$form, $color, $name],
404                   -fill => $color);
405           }
406
407           # This gets the real name (not current, blue/red, square/circle)
408           # Note: you'll want to return a list in realistic situations...
409           sub get_name {
410               my ($can) = @_;
411               my $item = $can->find('withtag', 'current');
412               my @taglist = $can->gettags($item);
413               my $name;
414               foreach (@taglist) {
415                   next if ($_ eq 'current');
416                   next if ($_ eq 'red' or $_ eq 'blue');
417                   next if ($_ eq 'square' or $_ eq 'circle');
418                   $name = $_;
419                   last;
420               }
421               return $name;
422           }
423
424           sub handle_circle {
425               my ($can) = @_;
426               my $name = get_name($can);
427               print "Action on circle $name...\n";
428           }
429
430           sub handle_blue {
431               my ($can) = @_;
432               my $name = get_name($can);
433               print "Action on blue item $name...\n";
434           }
435

Perl/Tk and Unicode

437       Perl/Tk follows Perl's model of handling Unicode. That is, if a string
438       is correctly flagged as a "character" string in the sense like
439       described in "TERMINOLOGY" in Encode, then Perl/Tk will very probably
440       display and handle this string correctly.
441
442       Note that every variable which is passed somehow into a Perl/Tk method
443       will be implicitely changed into an internally utf8-flagged variable.
444       Semantically nothing changes, as the series of codepoints stays the
445       same, but things will change when variables with high-bit iso-8859-1
446       characters will be passed to the "outer" world. In this case you have
447       to explicitely mark the encoding of your output stream if using IO, or
448       encode the variables using Encode for other style of communication.
449
450       This is the theory, now some examples.
451
452       If you use non-iso-8859-1 characters in the source code, then use
453       either the "use utf8;" or "use encoding 'encodingname'" pragma:
454
455            use utf8;
456            use Tk;
457            my $x = "some characters using utf8 encoding";
458            tkinit->Label(-text => $x)->pack;
459            MainLoop;
460
461       For data that comes from a file you have to specify the encoding unless
462       it's encoded as ascii or iso-8559-1:
463
464            use Tk;
465            open my $FH, "<:encoding(utf-8)", "filename" or die $!;
466            # or for utf-16 data: open my $FH, "<:encoding(utf-16)", "filename" or die $!;
467            my $data = <$FH>;
468            tkinit->Label(-text => $data)->pack;
469            MainLoop;
470
471       Likewise, the encoding must be specified for all data which is read
472       from Tk widgets and that shall be output into a file. For the output,
473       the encoding should be always specified, even if it is iso-8859-1:
474
475            use Tk;
476            $mw = tkinit;
477            $mw->Entry(-textvariable => \$input)->pack;
478            $mw->Button(
479                -text => "Write to file",
480                -command => sub {
481                    open my $FH, ">:encoding(iso-8859-1)", "filename" or die $!;
482                    print $FH $input;
483                },
484            )->pack;
485            MainLoop;
486
487       Note that Tk is Unicode-capable. So you need to be prepared that the
488       user has the appropriate input methods activated to enter non-ascii
489       characters. If an output encoding is used which does not cover the
490       whole of Unicode codepoints then a warning will be issued when writing
491       the file, like this:
492
493           "\x{20ac}" does not map to iso-8859-1 at /usr/local/lib/perl5/site_perl/5.8.8/mach/Tk.pm line 250.
494
495       Also, the same hexadecimal notation will be used as replacements for
496       the unhandled characters.
497
498       Handling encoding in I/O is pretty simple using the "encoding" PerlIO
499       layer, as described above. In other cases, such as when dealing with
500       databases, encoding the data usually has to be done manually, unless
501       the database driver has some means for automatically do this for you.
502       So when working with a MySQL database, one could use:
503
504            use Tk;
505            use DBI;
506            use Encode qw(encode);
507            $mw = tkinit;
508            $mw->Entry(-textvariable => \$input)->pack;
509            $mw->Button(
510                -text => "Write to database",
511                -command => sub {
512                    my $dbh = DBI->connect("dbi:mysql:test", "root", "") or die;
513                    my $encoded_input = encode("iso-8859-1", $input);
514                    $dbh->do("INSERT INTO testtable VALUES (?)", undef, $encoded_input) or die;
515                },
516            )->pack;
517            MainLoop;
518
519       Unfortunately, there are still places in Perl ignorant of Unicode. One
520       of these places are filenames. Consequently, the file selectors in
521       Perl/Tk do not handle encoding of filenames properly. Currently they
522       suppose that filenames are in iso-8859-1 encoding, at least on Unix
523       systems. As soon as Perl has a concept of filename encodings, then
524       Perl/Tk will also implement such schemes.
525
526
527
528perl v5.32.0                      2020-07-28                      UserGuide(3)
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