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<a name="sec-adjustment-internals"></a>Adjustment Internals</h2></div></div></div>
<p>
OK, you say, that's nice, but what if I want to create my own handlers to
respond when the user adjusts a <code class="classname">Range</code> widget or a
<code class="classname">SpinButton</code>. To access the value of a
<code class="classname">Gtk::Adjustment</code>, you can use the
<code class="methodname">get_value()</code> and <code class="methodname">set_value()</code> methods:
</p>
<p>
As mentioned earlier, <code class="classname">Gtk::Adjustment</code> can emit signals.
This is, of course, how updates happen automatically when you share an
<code class="classname">Adjustment</code> object between a
<code class="classname">Scrollbar</code> and another adjustable widget; all adjustable
widgets connect signal handlers to their adjustment's
<code class="literal">value_changed</code> signal, as can your program.
</p>
<p>
So, for example, if you have a <code class="classname">Scale</code> widget, and you
want to change the rotation of a picture whenever its value changes, you would
create a signal handler like this:
</p>
<pre class="programlisting"><code class="code">void cb_rotate_picture(MyPicture* picture)
{
picture->set_rotation(adj->get_value());
...</code></pre>
<p>
and connect it to the scale widget's adjustment like this:
</p>
<pre class="programlisting"><code class="code">adj->signal_value_changed().connect(sigc::bind<MyPicture*>(sigc::mem_fun(*this,
&cb_rotate_picture), picture));</code></pre>
<p>
What if a widget reconfigures the <em class="parameter"><code>upper</code></em> or
<em class="parameter"><code>lower</code></em> fields of its <code class="classname">Adjustment</code>,
such as when a user adds more text to a text widget? In this case, it emits
the <code class="literal">changed</code> signal.
</p>
<p>
<code class="classname">Range</code> widgets typically connect a handler to this
signal, which changes their appearance to reflect the change - for example, the
size of the slider in a scrollbar will grow or shrink in inverse proportion to
the difference between the <em class="parameter"><code>lower</code></em> and
<em class="parameter"><code>upper</code></em> values of its
<code class="classname">Adjustment</code>.
</p>
<p>
You probably won't ever need to attach a handler to this signal, unless you're
writing a new type of range widget.
</p>
<pre class="programlisting"><code class="code">adjustment->signal_changed();</code></pre>
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