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<html>
<head>
<meta name="description" content="Pmw - a toolkit for building high-level compound widgets in Python">
<meta name="content" content="python, megawidget, mega widget, compound widget, gui, tkinter">
<title>How to use Pmw megawidgets</title>
</head>
<body bgcolor="#ffffff" text="#000000" link="#0000ee"
vlink="551a8b" alink="ff0000">
<h1 ALIGN="CENTER">How to use Pmw megawidgets</h1>
<center><P ALIGN="CENTER">
<IMG SRC = blue_line.gif ALT = "" WIDTH=320 HEIGHT=5>
</p></center>
<dl>
<dt> <h3>Introduction</h3></dt><dd>
<p>
This document briefly describes the features of the Pmw megawidget
toolkit and how to use the megawidgets. Using examples, it
describes those features common to all Pmw megawidgets. For a
description of individual Pmw megawidgets see the
<a href="refindex.html">reference manuals</a>.
For complete information on general Pmw megawidget functionality see the
<a href="MegaArchetype.html">Pmw.MegaArchetype reference manual</a>.
For a lot more example code, run any of the files in the
Pmw <code>demos</code> directory.
</p>
<p>
A simple example of a megawidget is a counter. This widget
contains an entry field and two small arrow buttons. Users may
enter a value directly into the entry field or they may use the
buttons to increment and decrement the value displayed without
having to use the keyboard. Having this and other megawidgets in
your toolbox allows you to choose the best graphical interface for
your application.
</p>
</dd>
<dt> <h3>Getting started</h3></dt><dd>
<b>Initialisation of Pmw</b>
<br>
<p>
To run the examples in the tutorial, make sure that the
Pmw <code>lib</code> directory is in <code>sys.path</code>. You
should be able to cut and paste the examples into an interactive
python session, or you can copy them to a file and run the file with
python.
</p>
<p>
The following two lines should be entered before any of the
examples. These import and initialise Pmw.
For more information on <code>Pmw.initialise()</code> see the
<a href="PmwFunctions.html">Pmw functions reference manual</a>.
</p>
<dl>
<dd>
<pre>
import Pmw
root = Pmw.initialise()
</pre>
</dd>
</dl>
<p>
If necessary, you can have more control over how Tkinter and Pmw are
initialised by using this form of initialisation:
</p>
<dl>
<dd>
<pre>
import Tkinter
root = Tkinter.Tk()
import Pmw
Pmw.initialise(root)
</pre>
</dd>
</dl>
</dd>
<dt> <h3>Megawidget construction</h3></dt><dd>
<b>Creating a counter</b>
<br>
<p>
Now that you have the formalities out of the way, you can create and
pack a counter megawidget (see
<a href="Counter.html">Pmw.Counter reference manual</a>) using
its default configuration like this:
</p>
<dl>
<dd>
<pre>
counter1 = Pmw.Counter()
counter1.pack(padx = 10, pady = 10)
</pre>
</dd>
</dl>
<p>
Now enter a number and click on the arrow buttons to see the number
increment or decrement. The result looks something like this:
</p>
<center><P ALIGN="CENTER">
<IMG SRC = counter1.gif ALT = "Counter 1" WIDTH=220 HEIGHT=46>
</p></center>
<p>
The above example creates the counter as a child of the root window.
If you want to create it as a child of another window (for example,
a Tkinter.Frame widget called 'frame'), add the parent as an
argument to the constructor:
</p>
<dl>
<dd>
<pre>
counter1a = Pmw.Counter(frame)
</pre>
</dd>
</dl>
</dd>
<dt> <h3>Methods</h3></dt><dd>
<p>
Once a megawidget has been created, you can call any of its other
methods in a similar way to Tk widgets. The following sets the value
of the counter and then increments it:
</p>
<dl>
<dd>
<pre>
counter1.setentry(41)
counter1.increment()
</pre>
</dd>
</dl>
</dd>
<dt> <h3>Options</h3></dt><dd>
<p>
Like any widget, a megawidget may have options to allow it to be
configured for a particular use. Options allow the megawidget user
to modify the appearance and behaviour of the megawidget. The
counter megawidget has several such options. One of them,
<strong>datatype</strong>, specifies how the counter should count up
and down, such as, for example, by integers, reals, times or dates.
The default value is <strong>'numeric'</strong>, which means the
counter expects integers to be entered and will support
incrementing and decrementing by whole numbers.
</p>
<p>
Another option is
<strong>increment</strong>, which specifies how many units should be
added or subtracted when the counter is incremented or decremented.
Using these options, you can create a time counter, supporting the
format <strong>HH:MM:SS</strong>, and counting in minutes, like
this (note also the call to the <code>setentry</code> method to set
the contents of the entry field):
</p>
<dl>
<dd>
<pre>
counter2 = Pmw.Counter(
datatype = 'time',
increment = 60)
counter2.setentry('00:00:00')
counter2.pack(padx = 10, pady = 10)
</pre>
</dd>
</dl>
<p>
Many megawidget options can be modified using the
<code>configure()</code> method. For example, you can change the
value of the <strong>increment</strong> option to 10 minutes like
this:
</p>
<dl>
<dd>
<pre>
counter2.configure(increment = 60 * 10)
</pre>
</dd>
</dl>
<b>Initialisation options</b>
<br>
<p>
Some megawidget options can only be set when creating the megawidget.
These options can not be set by calling the <code>configure()</code>
method, but they can be queried in all the usual ways. For example,
the counter has an <strong>orient</strong> initialisation option
which specifies whether the arrow buttons should appear to the
left and right of the entry field (<strong>'horizontal'</strong>)
or above and below (<strong>'vertical'</strong>). You can create a
numeric counter with arrow buttons above and below the entry
field like this:
</p>
<dl>
<dd>
<pre>
counter3 = Pmw.Counter(orient = 'vertical')
counter3.pack(padx = 10, pady = 10)
</pre>
</dd>
</dl>
<b>Querying options</b>
<br>
<p>
You can query the value of megawidget options (initialisation or
not) in similar ways as for normal Tkinter widgets. For example,
the following code prints the values of some of the counter options.
</p>
<dl>
<dd>
<pre>
print counter3.cget('increment')
--> 1
print counter3.configure('orient')
--> ('orient', 'orient', 'Orient', 'horizontal', 'vertical')
</pre>
</dd>
</dl>
<p>
When a Tk widget option is queried, its value is always
returned as a string, regardless of the type used when setting the
option. However, when a Pmw megawidget option is queried, a
reference to the object used when setting the option is returned.
In other words it is not always a string. For example, the type
returned by <code>cget('increment')</code> above was integer.
</p>
</dd>
<dt> <h3>Components</h3></dt><dd>
<p>
Megawidgets are made up of other widgets, which we call
<em>components</em>. Each component is known by a logical name and
may be either a simple Tk widget, or may itself be a megawidget.
Pmw gives the megawidget user access to not only the functionality
supported directly by the megawidget through its options and methods,
but also to the components of the megawidget and their options and
methods. To access a component directly, use the
<code>component()</code> method. For example, to call method
<strong>doit</strong> of component <strong>comp</strong>
of megawidget <strong>mega</strong>:
</p>
<dl>
<dd>
<pre>
mega.component('comp').doit()
</pre>
</dd>
</dl>
<b>Component options</b>
<br>
<p>
There is a short-hand way to access the options of components, by
using the notation <em>component_option</em>. This allows, for
example, a counter megawidget to be configured with different
colored backgrounds for each of its arrow button components (these
components are called <strong>downarrow</strong> and
<strong>uparrow</strong>):
</p>
<dl>
<dd>
<pre>
counter2.configure(
downarrow_background = 'green',
uparrow_background = 'red')
</pre>
</dd>
</dl>
<b>The hull</b>
<br>
<p>
All megawidgets are enclosed in a containing widget which is created
automatically by the Pmw base classes. For normal megawidgets the
container is a Tkinter Frame widget. For megawidgets which are
toplevel windows, the container is a Tkinter Toplevel widget. The
containing widget is accessible as the <strong>hull</strong>
component.
</p>
<p>
To access options of the containing widget use the form
<strong>hull_</strong><em>option</em>. For example to create a
counter megawidget with a wide sunken border around it:
</p>
<dl>
<dd>
<pre>
counter4 = Pmw.Counter(
hull_relief = 'sunken',
hull_borderwidth = 5
)
</pre>
</dd>
</dl>
<b>The interior</b>
<br>
<p>
Some megawidgets, such as Dialog and LabeledWidget, also have a
frame into which users can pack other widgets. This frame may be a
component but can also be accessed with the <code>interior()</code>
method. For the Pmw.MegaToplevel and Pmw.MegaWidget classes, the
interior widget is the same as the hull widget. For other
megawidgets, the hull is the outer, containing widget and the
interior is the empty frame which can be used to extend the
megawidget by including extra internal widgets.
</p>
<b>Sub components and aliases</b>
<br>
<p>
Components may themselves be megawidgets and so their
(sub-)components can be referred to using the notation
<em>component_sub-component</em>. For example, the
<strong>entryfield</strong> component of the counter is a
Pmw.EntryField megawidget (which handles the input validation). In
turn, this has a Tkinter.Entry component named
<strong>entry</strong>. Therefore, you can change the background of
the counter's Tkinter.Entry widget with:
</p>
<dl>
<dd>
<pre>
counter2.configure(entryfield_entry_background = 'yellow')
</pre>
</dd>
</dl>
<p>
Most component path names (like <strong>entryfield_entry</strong>)
have a shorter <strong>alias</strong> defined for them. In this
case, you can use the equivalent:
</p>
<dl>
<dd>
<pre>
counter2.configure(entry_background = 'yellow')
</pre>
</dd>
</dl>
<b>Changing the python class of a component</b>
<br>
<p>
Each megawidget component is an instance of some python class. The
default class of each component is given in the reference manual.
By using the special <strong>pyclass</strong> component option, you
can specify a different python class to use when creating the
component. For example, to create a Pmw.Counter megawidget which
has a Tkinter.Button as its label, rather than the default
Tkinter.Label:
</p>
<dl>
<dd>
<pre>
counter5 = Pmw.Counter(
labelpos = 'w',
label_text = 'Hello',
label_pyclass = Tkinter.Button
)
</pre>
</dd>
</dl>
</dd>
<dt> <h3>Forwarding methods</h3></dt><dd>
<p>
Since a Pmw megawidget is a normal python class, it both inherits
methods from its base classes and also may have other methods
defined for it in the usual way.
Pmw also supports a third way that a megawidget may gain methods -
by 'forwarding' methods to one or more of its subwidgets. This is
also known as 'delegating'.
For example, a Pmw.Counter megawidget delegates the methods related
to its Pmw.EntryField component, <strong>entryfield</strong>, to the
component. It does not have to explicitely define methods which
call the component methods.
This is why we can call <strong>counter2.setentry()</strong> - since
<strong>setentry()</strong> is a method of the Pmw.EntryField
component, it is available to the Pmw.Counter.
</p>
<p>
Methods already defined by a class or its base classes take
precedence over delegated methods. For example, Pmw.Counter
inherits a <strong>cget</strong> method from Pmw.MegaArchetype.
Therefore, this method is not delegated to the <strong>cget</strong>
method of Pmw.EntryField.
</p>
</dd>
<dt> <h3>Extending Pmw megawidgets</h3></dt><dd>
<p>
There are several ways of extending Pmw megawidgets. Firstly, the
flexibility of the options and components allows the widget's
appearance and behaviour to be greatly modified. Secondly, widgets
of the user's choice can be added inside some megawidgets by using
the interior() method. The Pmw classes MegaToplevel, MegaWidget,
Dialog and LabeledWidget are particularly designed to be extended in
this way. For example, to create a dialog window containing a
counter:
</p>
<dl>
<dd>
<pre>
dialog = Pmw.Dialog(
title = 'Counter dialog',
buttons = ('OK', 'Cancel'))
interior = dialog.interior()
counter = Pmw.Counter(interior)
counter.pack(padx = 20, pady = 20)
</pre>
</dd>
</dl>
<center><P ALIGN="CENTER">
<IMG SRC = counter2.gif ALT = "Counter 2" WIDTH=266 HEIGHT=126>
</p></center>
<p>
A third way to extend megawidgets is to inherit from (or subclass)
them. See <a href="howtobuild.html">How to build Pmw
megawidgets</a> for information on how to use inheritance to extend
a megawidget by adding new options. For simpler cases, where new
methods are to be added to an existing megawidget and/or the default
values for some options are to be changed, normal subclassing can be
used. For example, to create new classes based on a Pmw.Counter,
one with a new method <code>getminutes()</code> and one with a
default datatype of 'time' and a white entry background:
</p>
<dl>
<dd>
<pre>
class MinuteCounter1(Pmw.Counter):
def getminutes(self):
return Pmw.timestringtoseconds(self.getvalue()) / 60
class MinuteCounter2(Pmw.Counter):
def __init__(self, parent = None, **kw):
kw['datatype'] = 'time'
kw['entry_background'] = 'white'
kw['entryfield_value'] = '00:00:00'
kw['increment'] = 60
apply(Pmw.Counter.__init__, (self, parent), kw)
</pre>
</dd>
</dl>
</dd>
<dt> <h2>A quick example</h2></dt><dd>
<p>
The following code is a small example of how to use Pmw megawidgets.
It is a complete program which displays three ways for the user to
enter a value - using an up-down counter, an entry field with
validation and a dropdown combobox.
</p>
<dl>
<dd>
<pre>
import Pmw
root = Pmw.initialise(fontScheme = 'pmw1')
counter = Pmw.Counter(
label_text = 'Counter:',
labelpos = 'w',
entryfield_value = '00:00:00',
entryfield_validate = 'time',
datatype='time',
increment=5*60,
)
counter.pack(fill = 'x', padx = 10, pady = 10)
entry = Pmw.EntryField(
label_text = 'Real entry:',
labelpos = 'w',
value = '+2.9979e+8',
validate = 'real',
)
entry.pack(fill = 'x', padx = 10, pady = 10)
combo = Pmw.ComboBox(
label_text = 'ComboBox:',
labelpos = 'w',
scrolledlist_items = map(str, range(20))
)
combo.pack(fill = 'x', padx = 10, pady = 10)
# Make the labels line up neatly
Pmw.alignlabels((counter, entry, combo))
root.title('Pmw megawidgets example')
root.mainloop()
</pre>
</dd>
</dl>
<center><P ALIGN="CENTER">
<IMG SRC = example1.gif ALT = "Example 1" WIDTH=321 HEIGHT=140>
</p></center>
</dd>
<dt> <h3>Another example</h3></dt><dd>
<p>
The following also shows how to use Pmw megawidgets. It displays a
RadioSelect megawidget and an exit button packed into the root
window.
</p>
<dl>
<dd>
<pre>
import Tkinter
import Pmw
def callback(tag):
# This is called whenever the user clicks on a
# button in the RadioSelect widget.
print tag, 'was pressed.'
# Initialise Tkinter and Pmw.
root = Pmw.initialise(fontScheme = 'pmw1')
root.title('Pmw RadioSelect demonstration')
# Create and pack a RadioSelect widget.
radio = Pmw.RadioSelect(
command = callback,
labelpos = 'w',
label_text = 'Food group:')
radio.pack(padx = 20, pady = 20)
# Add some buttons to the RadioSelect.
for text in ('Fruit', 'Vegetables', 'Cereals', 'Legumes'):
radio.add(text)
radio.invoke('Vegetables')
# Create an exit button.
exit = Tkinter.Button(text = 'Exit', command = root.destroy)
exit.pack(pady = 20)
# Let's go.
root.mainloop()
</pre>
</dd>
</dl>
<center><P ALIGN="CENTER">
<IMG SRC = example2.gif ALT = "Example 2" WIDTH=503 HEIGHT=158>
</p></center>
</dd>
<dt> <h3>Using the Tk option database</h3></dt><dd>
<p>
There are several ways to use the Tk option database to customise a
Pmw application. Firstly you can customise all the basic Tk widgets
in the usual way. For example, to set the background of all
Tkinter.Label widgets (whether a megawidget component or not):
</p>
<dl>
<dd>
<pre>
root.option_add('*Label.background', 'pink')
</pre>
</dd>
</dl>
<p>
To set the background of all Pmw.EntryField <strong>label</strong>
components:
</p>
<dl>
<dd>
<pre>
root.option_add('*EntryField.Label.background', 'green')
</pre>
</dd>
</dl>
<p>
To set the background of all Pmw.EntryField components, including
the <strong>hull</strong> component:
</p>
<dl>
<dd>
<pre>
root.option_add('*EntryField*background', 'blue')
</pre>
</dd>
</dl>
<p>
The above option settings affect basic Tk widgets and, since it is
built into the Tk widgets, this functionality is always available.
However, to be able to use the Tk option database to set the default
values for Pmw megawidget options, <code>Pmw.initialise()</code>
must be called with <code>useTkOptionDb = 1</code>. If this is not
done, Pmw does not query the Tk option database for megawidget
option defaults. This is the default behaviour because there is a
slight performance penalty for using the Tk option database.
</p>
<p>
Assuming <code>useTkOptionDb</code> has been set, the default
buttonbox position of all Pmw.Dialog megawidgets can be changed
with:
</p>
<dl>
<dd>
<pre>
root.option_add('*Dialog.buttonboxpos', 'e')
</pre>
</dd>
</dl>
<p>
To set the label position of all Pmw.EntryField megawidgets, thus giving
them a <strong>label</strong> component by default:
</p>
<dl>
<dd>
<pre>
root.option_add('*EntryField.labelpos', 'w')
</pre>
</dd>
</dl>
</dd>
</dl>
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Pmw 1.2 -
5 Aug 2003
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