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<?xml version="1.0" encoding="utf-8"?>
<page xmlns="http://projectmallard.org/1.0/" xmlns:its="http://www.w3.org/2005/11/its" xmlns:xi="http://www.w3.org/2001/XInclude" type="guide" style="task" id="scale.py" xml:lang="ca">
<info>
<title type="text">Scale (Python)</title>
<link type="guide" xref="beginner.py#entry"/>
<link type="seealso" xref="grid.py"/>
<link type="next" xref="textview.py"/>
<revision version="0.2" date="2012-06-23" status="draft"/>
<credit type="author copyright">
<name>Marta Maria Casetti</name>
<email its:translate="no">mmcasetti@gmail.com</email>
<years>2012</years>
</credit>
<desc>A slider widget for selecting a value from a range</desc>
</info>
<title>Scale</title>
<media type="image" mime="image/png" src="media/scale.png"/>
<p>Slide the scales!</p>
<links type="section"/>
<section id="code">
<title>Code used to generate this example</title>
<code mime="text/x-python" style="numbered">from gi.repository import Gtk
import sys
class MyWindow(Gtk.ApplicationWindow):
def __init__(self, app):
Gtk.Window.__init__(self, title="Scale Example", application=app)
self.set_default_size(400, 300)
self.set_border_width(5)
# two adjustments (initial value, min value, max value,
# step increment - press cursor keys to see!,
# page increment - click around the handle to see!,
# page size - not used here)
ad1 = Gtk.Adjustment(0, 0, 100, 5, 10, 0)
ad2 = Gtk.Adjustment(50, 0, 100, 5, 10, 0)
# an horizontal scale
self.h_scale = Gtk.Scale(
orientation=Gtk.Orientation.HORIZONTAL, adjustment=ad1)
# of integers (no digits)
self.h_scale.set_digits(0)
# that can expand horizontally if there is space in the grid (see
# below)
self.h_scale.set_hexpand(True)
# that is aligned at the top of the space allowed in the grid (see
# below)
self.h_scale.set_valign(Gtk.Align.START)
# we connect the signal "value-changed" emitted by the scale with the callback
# function scale_moved
self.h_scale.connect("value-changed", self.scale_moved)
# a vertical scale
self.v_scale = Gtk.Scale(
orientation=Gtk.Orientation.VERTICAL, adjustment=ad2)
# that can expand vertically if there is space in the grid (see below)
self.v_scale.set_vexpand(True)
# we connect the signal "value-changed" emitted by the scale with the callback
# function scale_moved
self.v_scale.connect("value-changed", self.scale_moved)
# a label
self.label = Gtk.Label()
self.label.set_text("Move the scale handles...")
# a grid to attach the widgets
grid = Gtk.Grid()
grid.set_column_spacing(10)
grid.set_column_homogeneous(True)
grid.attach(self.h_scale, 0, 0, 1, 1)
grid.attach_next_to(
self.v_scale, self.h_scale, Gtk.PositionType.RIGHT, 1, 1)
grid.attach(self.label, 0, 1, 2, 1)
self.add(grid)
# any signal from the scales is signaled to the label the text of which is
# changed
def scale_moved(self, event):
self.label.set_text("Horizontal scale is " + str(int(self.h_scale.get_value())) +
"; vertical scale is " + str(self.v_scale.get_value()) + ".")
class MyApplication(Gtk.Application):
def __init__(self):
Gtk.Application.__init__(self)
def do_activate(self):
win = MyWindow(self)
win.show_all()
def do_startup(self):
Gtk.Application.do_startup(self)
app = MyApplication()
exit_status = app.run(sys.argv)
sys.exit(exit_status)
</code>
</section>
<section id="methods">
<title>Useful methods for a Scale widget</title>
<p>A Gtk.Adjustment is needed to construct the Gtk.Scale. This is the representation of a value with a lower and upper bound, together with step and page increments, and a page size, and it is constructed as <code>Gtk.Adjustment(value, lower, upper, step_increment, page_increment, page_size)</code> where the fields are of type <code>float</code>; <code>step_increment</code> is the increment/decrement that is obtained by using the cursor keys, <code>page_increment</code> the one that is obtained clicking on the scale itself. Note that <code>page_size</code> is not used in this case, it should be set to <code>0</code>.</p>
<p>In line 28 the signal <code>"value-changed"</code> is connected to the callback function <code>scale_moved()</code> using <code><var>widget</var>.connect(<var>signal</var>, <var>callback function</var>)</code>. See <link xref="signals-callbacks.py"/> for a more detailed explanation.</p>
<list>
<item><p><code>get_value()</code> retrieves the current value of the scale; <code>set_value(value)</code> sets it (if the <code>value</code>, of type <code>float</code>, is outside the minimum or maximum range, it will be clamped to fit inside them). These are methods of the class Gtk.Range.</p></item>
<item><p>Use <code>set_draw_value(False)</code> to avoid displaying the current value as a string next to the slider.</p></item>
<item><p>To highlight the part of the scale between the origin and the current value:</p>
<code mime="text/x-python">
self.h_scale.set_restrict_to_fill_level(False)
self.h_scale.set_fill_level(self.h_scale.get_value())
self.h_scale.set_show_fill_level(True)</code>
<p>in the callback function of the "value-changed" signal, so to have the new filling every time the value is changed. These are methods of the class Gtk.Range.</p>
</item>
<item><p><code>add_mark(value, position, markup)</code> adds a mark at the <code>value</code> (<code>float</code> or <code>int</code> if that is the precision of the scale), in <code>position</code> (<code>Gtk.PositionType.LEFT, Gtk.PositionType.RIGHT, Gtk.PositionType.TOP, Gtk.PositionType.BOTTOM</code>) with text <code>Null</code> or <code>markup</code> in the Pango Markup Language. To clear marks, <code>clear_marks()</code>.</p></item>
<item><p><code>set_digits(digits)</code> sets the precision of the scale at <code>digits</code> digits.</p></item>
</list>
</section>
<section id="references">
<title>API References</title>
<p>In this sample we used the following:</p>
<list>
<item><p><link href="http://developer.gnome.org/gtk3/unstable/GtkScale.html">GtkScale</link></p></item>
<item><p><link href="http://developer.gnome.org/gtk3/unstable/GtkAdjustment.html">GtkAdjustment</link></p></item>
<item><p><link href="http://developer.gnome.org/gtk3/unstable/gtk3-Standard-Enumerations.html">Standard Enumerations</link></p></item>
</list>
</section>
</page>
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