NAME¶
Tkx::Tutorial - How to use Tkx
DESCRIPTION¶
Tk is a toolkit for creating applications with graphical interfaces on
Windows, Mac OS X and X11. The Tk toolkit is native to the
Tcl
programming language, but its ease of use and cross-platform availability has
made it the GUI toolkit of choice for many other dynamic languages.
Tkx is a Perl module that makes the Tk toolkit available to Perl
programs. By loading the Tkx module Perl programs can create windows and fill
them with text, images, buttons and other controls that make up the user
interface of the application.
Hello World¶
Let's start with the mandatory exercise of creating an application that greats
the world. We'll make the application window contain a single button which
will shut down the application if clicked. The code to make this happen is:
use Tkx;
Tkx::button(".b",
-text => "Hello, world",
-command => sub { Tkx::destroy("."); },
);
Tkx::pack(".b");
Tkx::MainLoop()
Save this to a file called
hello.pl and then run "perl
hello.pl" to start the application. A window with the text "Hello,
world" should appear on your screen. Let's look at what this code is
doing.
After the Tkx module has been loaded by the "use Tkx" statement, the
application will show an empty window called ".". We create a
button with the name ".b" and tell the window to display the
button with the call to "Tkx::pack()". After the layout of the
window has been set up, we need to pass control back to Tk so that it can draw
the window and invoke our callback if the button is clicked. This is done with
the "Tkx::MainLoop()" call at the end. Clicking the button will
invoke the subroutine registered with the button's "-command"
option. In this case the callback destroys the window, which in turn
terminates the application.
For reference, this is how the same program would look in Tcl:
package require Tk
button .b \
-text "Hello, world" \
-command { destroy . }
pack .b
This program can be executed by the
tclsh binary that comes with Tcl/Tk.
As you can see the code is mostly identical, but with a slightly different
syntax. The only difference is that the call to
MainLoop() is implicit
in Tcl and does not have to be spelled out.
Tkx does not include documentation for all the Tk widgets available for use.
Instead you will need to read the mostly excellent documentation that comes
with Tcl/Tk and extrapolate the Tkx syntax. This translation is relatively
straightforward and basically involves adding the prefix "Tkx::" to
all the functions and passing arguments with Perl syntax (as with the
Tkx::button examples above). The Tk documentation can be found here:
<
http://aspn.activestate.com/ASPN/docs/ActiveTcl/at.pkg_index.html>.
This documents core Tk and useful add-on packages that are part of ActiveTcl.
The ActiveTcl HTML documentation can also be downloaded from
<
http://downloads.activestate.com/ActiveTcl/html/> and installed
locally. The official Tcl/Tk docs are found at <
http://www.tcl.tk/doc/>.
A major complication in the mapping to Perl is how to invoke subcommands on Tk
widgets. For example, if you want to change the text of the button created
above you might in Tcl do:
.b configure -text "Goodbye, cuel world"
a literal translation to Tkx would be:
Tkx::.b("configure", -text => "Goodbye, cruel world");
or
Tkx::.b_configure(-text => "Goodbye, cruel world");
but neither of those work as you can't use "." as part of function
names in Perl. Because of this we almost always use objects when working with
Tkx widgets.
Hello World with objects¶
The windows and controls that make up a Tk interface are called
widgets.
The widgets are identified by path names of the form ".foo.bar.baz".
These names are hierarchical in the same way as file system names are, but
"." is used instead of "/" to separate levels. The name
".foo.bar.baz" is the name of a widget that is child of widget
".foo.bar" which in turn is a child of ".foo". At the top
of this hierarchy we have a widget called ".", which is the main
window of the application.
The Tkx module provides the "Tkx::widget" class, which can be used to
hide the details of Tk path names from Tkx applications. This provide a more
"perlish" way to create and manipulate Tk widgets. It also provide a
convenient way to invoke subcommands (methods) on the widgets.
Our "Hello, world" program can be rewritten like this using the
"Tkx::widget" class:
use Tkx;
my $mw = Tkx::widget->new(".");
my $b = $mw->new_button(
-text => "Hello, world",
-command => sub { $mw->g_destroy; },
);
$b->g_pack;
Tkx::MainLoop()
By loading the Tkx module, we make the "Tkx::widget" class available
and create the main window (the widget called "."). Next, we
instantiate a new "Tkx::widget" object wrapping the main window. It
is customary to name this object $mw.
To create a new button child widget we call the "$mw->new_button"
method. Constructor methods are always prefixed with "new_". The
rest of the method name is the name of the Tk widget to create; i.e.
"button" in this case. Arguments are passed as before.
Calling a "g_" method will invoke the corresponding Tk command with
the widget path as argument. In the code above we destroy the main window by
calling "$mw->g_destroy" and we pack the button in the main
window by invoking "$b->g_pack".
In the end the MainLoop is invoked as before.
For trivial programs like the one above, using "Tkx::widget" wrappers
does not appear to be very helpful, but as the application grows and the Tk
path names get longer, the advantage is more noticeable.
Hello World expanded¶
The following, slightly expanded version of the previous Hello World program,
introduces a few more Tkx features. Line numbers have been added to the
program for easier to reference back to its statements:
1 use strict;
2 use Tkx;
3
4 my $mw = Tkx::widget->new(".");
5 $mw->g_wm_title("Hello, world");
6 $mw->g_wm_minsize(300, 200);
7
8 my $b;
9 $b = $mw->new_button(
10 -text => "Hello, world",
11 -command => sub {
12 $b->m_configure(
13 -text => "Goodbye, cruel world",
14 );
15 Tkx::after(1500, sub { $mw->g_destroy });
16 },
17 );
18 $b->g_pack(
19 -padx => 10,
20 -pady => 10,
21 );
22
23 Tkx::tk___messageBox(
24 -parent => $mw,
25 -icon => "info",
26 -title => "Tip of the Day",
27 -message => "Please be nice!",
28 );
29
30 Tkx::MainLoop()
The first thing we add is the "use strict" statement, because that's a
good practice in general.
In line 5 and 6 we set up some window manager attributes of the main application
window. We use underscore in the g_ method names where Tcl would use space
between words. The same rules apply to the function names in the
"Tkx::" namespace directly. We could alternatively have modified the
window attributes with:
Tkx::wm_title($mw, "Hello, world");
Tkx::wm_minsize($mw, 300, 200);
In Tcl, this would be:
wm title . "Hello, world"
wm minsize . 300 200
The rule is: A single underscore on the Perl side turns into space on the Tcl
side.
In line 11 to 16 we have expanded the button callback to change the text of
button and wait 1.5 seconds before shutting down the application. In addition
to the "g_" methods described in the previous section,
"Tkx::widget" also provides "m_" methods which are
forwarded as Tcl subcommands of the current widget. The most commonly used
subcommand is "configure" that is used to change the attributes of a
widget as we do in line 12. Since we now reference $b from the callback, we
had to declare the variable upfront in line 8 instead of declaring it together
with the assignment as we did previously. In line 15 we destroy the window
after a delay of 1500ms, which should be enough time to read the new
"Goodbye, cruel world" text.
The "m_" method prefix is optional, you might prefer to leave it out.
Line 18 adds padding around buttons, which is usually a good idea.
In line 23 we invoke the messageBox command to pop up a useful reminder to our
user. But what's up with the "tk___" prefix? In the Tcl docs you
will find that the name of this command is actually "tk_messageBox".
Remember the previous rule that an underscore in Tkx:: names turn into a space
on the Tcl side? If you try to call "Tkx::tk_messageBox()" you will
get an error telling you:
bad option "messageBox": must be appname, caret, scaling,
useinputmethods, or windowingsystem
What happens is that Tkx invoked the "tk messageBox" command, but the
Tcl "tk" command only takes the subcommands listed in the error
message above and refuse to do anything about "messageBox". In order
to invoke Tcl commands with underscore their name, you need to
triple
the underscore on the Perl side, which gives us
"Tkx::tk___messageBox()". Double underscores in names have yet
another meaning that we will tell you about in the next section.
Most real GUI application will need a menu line at the top of the application
window or screen. The following runnable program shows how a minimal menu can
be set up with Tkx:
1 #!/usr/bin/perl -w
2
3 use strict;
4 use Tkx;
5
6 our $VERSION = "1.00";
7
8 (my $progname = $0) =~ s,.*[\\/],,;
9 my $IS_AQUA = Tkx::tk_windowingsystem() eq "aqua";
10
11 Tkx::package_require("style");
12 Tkx::style__use("as", -priority => 70);
13
14 my $mw = Tkx::widget->new(".");
15 $mw->configure(-menu => mk_menu($mw));
16
17 Tkx::MainLoop();
18 exit;
19
20 sub mk_menu {
21 my $mw = shift;
22 my $menu = $mw->new_menu;
23
24 my $file = $menu->new_menu(
25 -tearoff => 0,
26 );
27 $menu->add_cascade(
28 -label => "File",
29 -underline => 0,
30 -menu => $file,
31 );
32 $file->add_command(
33 -label => "New",
34 -underline => 0,
35 -accelerator => "Ctrl+N",
36 -command => \&new,
37 );
38 $mw->g_bind("<Control-n>", \&new);
39 $file->add_command(
40 -label => "Exit",
41 -underline => 1,
42 -command => [\&Tkx::destroy, $mw],
43 ) unless $IS_AQUA;
44
45 my $help = $menu->new_menu(
46 -name => "help",
47 -tearoff => 0,
48 );
49 $menu->add_cascade(
50 -label => "Help",
51 -underline => 0,
52 -menu => $help,
53 );
54 $help->add_command(
55 -label => "\u$progname Manual",
56 -command => \&show_manual,
57 );
58
59 my $about_menu = $help;
60 if ($IS_AQUA) {
61 # On Mac OS we want about box to appear in the application
62 # menu. Anything added to a menu with the name "apple" will
63 # appear in this menu.
64 $about_menu = $menu->new_menu(
65 -name => "apple",
66 );
67 $menu->add_cascade(
68 -menu => $about_menu,
69 );
70 }
71 $about_menu->add_command(
72 -label => "About \u$progname",
73 -command => \&about,
74 );
75
76 return $menu;
77 }
78
79
80 sub about {
81 Tkx::tk___messageBox(
82 -parent => $mw,
83 -title => "About \u$progname",
84 -type => "ok",
85 -icon => "info",
86 -message => "$progname v$VERSION\n" .
87 "Copyright 2005 ActiveState. " .
88 "All rights reserved.",
89 );
90 }
We start out as all proper Perl programs should by enabling warnings and
stricture at line 1 and 3. Then, we load Tkx which will create our main
application window at line 4.
In line 9 we initialize the $IS_AQUA constant. Aqua is the native interface of
Mac OS X. We need this constant because the menu layout on Aqua is not the
same as in other windowing systems. Note that Tk on Mac OS X can be compiled
against either Aqua or X11. When our application runs under X11 we want to use
the standard Unix menu layout, so it would not be correct to just make our
code conditional on what operating system it runs under ("$^O eq
'darwin'" for Mac OS X).
In line 11 and 12 we override the default look&feel style of Tk to a more
modern variant. Tcl packages can be loaded with the
"Tkx::package_require()" function and we can access the Tcl command
"style::use" as "Tkx::style__use" in Perl, i.e. we need to
turn the double colon into a double underscore. More about Tcl packages and
namespaces in the next section.
In line 14, we obtain a "Tkx::widget" reference to the main window as
before, then set up the application menu by setting up the "-menu"
option of the main window in line 15.
In a real application there would be additional code between line 15 and 17 to
set up the rest of the application window, but for this demonstration we'll
just leave the window empty.
In line 17, we ask Tk to start processing events by invoking
"Tkx::MainLoop()". This function will return when the application
window has been destroyed. When that happens, we exit at line 18.
The application menu itself is set up and returned by the "mk_menu()"
function in line 20 to 77. This code should be easy enough to follow. Note how
we make
File | New and
Help | Foo Manual both reference
functions that are not yet written. The application will still run, but when
you try to invoke these menu entries you get an "Application Error
Dialog" from Tk. It is handy to be able to leave stubs like this around
during the development, just remember to add the "new" and
"show_manual" functions before the application ships.
The "-underline" options are provided to make it possible to select
menu entries with the keyboard. The corresponding character of the
"-label" will be underlined and you will be able to select this
entry by pressing the key when the menu is active.
It is also possible to set up direct keyboard shortcuts as we've done for the
File | New function at line 32. Note that the "-accelerator"
option only adds the text to the menu item, so we need to use an explicit call
to set up this binding in line 38.
For Aqua we don't want to add the "File | Exit" entry to the menu
because the OS itself always provide a Quit action in the application menu.
Aqua applications will also need to add the "About" function on the
application menu instead of the "Help" menu as is common on other
platforms.
The menu names "apple" and "help" provided in line 46 and 65
has special significance to Tk. Menu items added to the "apple" menu
will show up in the application menu. In Mac OS X these entries show up at the
top of the menu just right of the apple. If not provided, Tk provides its own
"About" entry that will tell you about what version of Tcl/Tk you
are using. A menu called "help" will be flushed right on Unix, even
though this style seems to be out of fashion in modern Unix applications.
The Tkx distribution contains a script called
menu which is a runnable
version of the program shown here. You might want to use this as a starting
point for your own Tkx applications.
Using Tcl packages¶
When the Perl application starts up and loads Tkx, the only functions available
in the "Tkx::" namespace are those commands provided by core Tcl/Tk.
These commands are described in the "Tcl" and "Tk"
sections at
<
http://aspn.activestate.com/ASPN/docs/ActiveTcl/at.pkg_index.html>.
Additional commands can be loaded from Tcl packages. Once loaded, new commands
show up in the "Tkx::" namespace. This example loads the
"Tktable" package in order to make the "table" command
available for createing
table widgets:
use Tkx;
Tkx::package_require("Tktable");
my $mw = Tkx::widget->new(".");
my $t = $mw->new_table(
-rows => 5,
-cols => 3,
);
$t->g_pack;
Tkx::MainLoop()
Packages are loaded by calling the "Tkx::package_require()" function
taking the package name as argument. An optional version number can be
provided as the second argument if you want to make sure a certain version or
newer is loaded.
One source of confusion here is the proper spelling of the package name to
provide to
Tkx::package_require(). The Tcl/Tk documentation will call
the package in the example above
TkTable (with two upper case
"T"s) and not really mention the exact spelling of the package name
(only one upper case "T"). In some cases the "synopsis"
section describing the package will spell out the package name, but in cases
like this we have found no better way than to look into the
pkgIndex.tcl files in the Tcl
lib/ area if loading the package
fails. The package documented as "BWidgets" should be loaded as
"BWidget" (without the "s") and the package documented as
"IWidgets" should be loaded as "Iwidgets" (with a lower
case "w").
Most modern Tcl packages do not create names at the top level like TkTable
above. Instead, they create functions in a Tcl namespace with a name matching
the package name. In the menu example of the previous section we loaded the
"style" package which created a command called "use" in
the "style" namespace. This command can be referenced as
"::style::use" or "style::use" from Tcl. From Perl this
maps to a function called "Tkx::style__use" (i.e. we replace the
double colon with double underscore and ignore the colon in the front). Read
Tkx for details about how sequences of "_" in "Tkx::"
names are mapped to Tcl names.
In Tkx applications it is often convenient to use your own subclass of
"Tkx::widget" where you can introduce shortcuts and adapters for the
raw Tcl commands. The following is an example class, which could be saved to
the file
MyWidget.pm:
1 package MyWidget;
2
3 use strict;
4 use base qw(Tkx::widget);
5 use Carp qw(croak);
6
7 sub messageBox {
8 my $self = shift;
9 return Tkx::tk___messageBox(-parent => $self, @_);
10 }
11
12 sub getOpenFile {
13 my $self = shift;
14 return Tkx::tk___getOpenFile(-parent => $self, @_);
15 }
16
17 sub bell {
18 my $self = shift;
19 Tkx::bell(-displayof => $self, @_);
20 }
21
30 sub pack {
31 my $self = shift;
32 $self->g_pack(@_);
33 return $self;
34 }
35
36 sub _nclass {
37 return __PACKAGE__;
38 }
39
40 1;
The main program would use it like this:
use Tkx;
use MyWidget;
my $mw = MyWidget->new(".");
$mw->messageBox(...);
...
Tkx::MainLoop();
The MyWidget class above provides shortcuts for the "messageBox" and
"getOpenFile" in order to hide the triple underscore ugliness and
propagate the "-parent" attribute. Similar reasoning exists for the
"bell".
The "pack" method is provided so that we can initialize and pack a
widget in the same statement and avoid repeated typing of the "g_"
method prefix:
my $b = $mw->new_button(...)->pack;
The "_nclass" method needs to be overridden so that any new widget
children created also end up as MyWidget objects. This method is called
internally by methods like "$mw->new_button(...)" to determine
which kind of object will wrap the newly created widget path.
Having you own application-specific widget class provides a place to add methods
discovered by refactoring repeated code in your application.
LICENSE¶
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.
Copyright 2005 ActiveState. All rights reserved.
SEE ALSO¶
Tkx
The bundled sample programs; tkx-ed, tkx-prove.