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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 7. Adjustments</title><meta name="generator" content="DocBook XSL Stylesheets V1.65.1"><link rel="home" href="index.html" title="PyGTK 2.0 Tutorial"><link rel="up" href="index.html" title="PyGTK 2.0 Tutorial"><link rel="previous" href="sec-RadioButtons.html" title="6.4. Radio Buttons"><link rel="next" href="sec-UsingAdjustmentsTheEasyWay.html" title="7.2. Using Adjustments the Easy Way"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 7. Adjustments</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="sec-RadioButtons.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="sec-UsingAdjustmentsTheEasyWay.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="ch-Adjustments"></a>Chapter 7. Adjustments</h2></div></div><div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ch-Adjustments.html#sec-CreatingAnAdjustment">7.1. Creating an Adjustment</a></span></dt><dt><span class="sect1"><a href="sec-UsingAdjustmentsTheEasyWay.html">7.2. Using Adjustments the Easy Way</a></span></dt><dt><span class="sect1"><a href="sec-AdjustmentInternals.html">7.3. Adjustment Internals</a></span></dt></dl></div><p>GTK has various widgets that can be visually adjusted by the user
using the mouse or the keyboard, such as the range widgets, described in the
Range Widgets section. There are also a few widgets that display some
adjustable portion of a larger area of data, such as the text widget and the
viewport widget.</p><p>Obviously, an application needs to be able to react to changes the
user makes in range widgets. One way to do this would be to have each widget
emit its own type of signal when its adjustment changes, and either pass the
new value to the signal handler, or require it to look inside the widget's
data structure in order to ascertain the value. But you may also want to
connect the adjustments of several widgets together, so that adjusting one
adjusts the others. The most obvious example of this is connecting a
scrollbar to a panning viewport or a scrolling text area. If each widget has
its own way of setting or getting the adjustment value, then the programmer
may have to write their own signal handlers to translate between the output
of one widget's signal and the "input" of another's adjustment setting
method.</p><p>GTK solves this problem using the
<tt class="classname">Adjustment</tt> object, which is not a widget but a way
for widgets to store and pass adjustment information in an abstract and
flexible form. The most obvious use of <tt class="classname">Adjustment</tt> is
to store the configuration parameters and values of range widgets, such as
scrollbars and scale controls. However, since
<tt class="classname">Adjustment</tt>s are derived from
<tt class="classname">Object</tt>, they have some special powers beyond those of
normal data structures. Most importantly, they can emit signals, just like
widgets, and these signals can be used not only to allow your program to
react to user input on adjustable widgets, but also to propagate adjustment
values transparently between adjustable widgets.</p><p>You will see how adjustments fit in when you see the other widgets
that incorporate them: Progress Bars, Viewports, Scrolled Windows, and
others.</p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sec-CreatingAnAdjustment"></a>7.1. Creating an Adjustment</h2></div></div><div></div></div><p>Many of the widgets which use adjustment objects do so
automatically, but some cases will be shown in later examples where you may
need to create one yourself. You create an adjustment using:</p><table border="0" bgcolor="#E0E0E0" width="100%"><tr><td><pre class="programlisting">
adjustment = gtk.Adjustment(<b class="parameter"><tt>value</tt></b>=0, <b class="parameter"><tt>lower</tt></b>=0, <b class="parameter"><tt>upper</tt></b>=0, <b class="parameter"><tt>step_incr</tt></b>=0, <b class="parameter"><tt>page_incr</tt></b>=0, <b class="parameter"><tt>page_size</tt></b>=0)
</pre></td></tr></table><p>The <i class="parameter"><tt>value</tt></i> argument is the initial value
you want to give to the <i class="parameter"><tt>adjustment</tt></i>, usually
corresponding to the topmost or leftmost position of an adjustable
widget. The <i class="parameter"><tt>lower</tt></i> argument specifies the lowest value
which the <i class="parameter"><tt>adjustment</tt></i> can hold. The
<i class="parameter"><tt>step_incr</tt></i> argument specifies the "smaller" of the two
increments by which the user can change the value, while the
<i class="parameter"><tt>page_incr</tt></i> is the "larger" one. The
<i class="parameter"><tt>page_size</tt></i> argument usually corresponds somehow to the
visible area of a panning widget. The <i class="parameter"><tt>upper</tt></i> argument
is used to represent the bottom most or right most coordinate in a panning
widget's child. Therefore it is not always the largest number that
<i class="parameter"><tt>value</tt></i> can take, since the
<i class="parameter"><tt>page_size</tt></i> of such widgets is usually non-zero.</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sec-RadioButtons.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="index.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sec-UsingAdjustmentsTheEasyWay.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">6.4. Radio Buttons </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 7.2. Using Adjustments the Easy Way</td></tr></table></div></body></html>
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