File: //usr/local/ssl/share/gtk-doc/html/gtk/checklist-modifiers.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Test for modifier keys correctly</title>
<meta name="generator" content="DocBook XSL Stylesheets V1.69.1">
<link rel="start" href="index.html" title="GTK+ Reference Manual">
<link rel="up" href="gtk-migrating-checklist.html" title="Migration Checklist">
<link rel="prev" href="checklist-gdkeventexpose-region.html" title="Use GdkEventExpose.region">
<link rel="next" href="checklist-named-icons.html" title="Use named icons">
<meta name="generator" content="GTK-Doc V1.6 (XML mode)">
<link rel="stylesheet" href="style.css" type="text/css">
<link rel="part" href="gtk.html" title="Part I. GTK+ Overview">
<link rel="part" href="gtkbase.html" title="Part II. GTK+ Core Reference">
<link rel="part" href="gtkobjects.html" title="Part III. GTK+ Widgets and Objects">
<link rel="chapter" href="ch01.html" title="Object Hierarchy">
<link rel="chapter" href="ch02.html" title="Widget Gallery">
<link rel="chapter" href="WindowWidgets.html" title="Windows">
<link rel="chapter" href="DisplayWidgets.html" title="Display Widgets">
<link rel="chapter" href="ButtonWidgets.html" title="Buttons and Toggles">
<link rel="chapter" href="NumericEntry.html" title="Numeric/Text Data Entry">
<link rel="chapter" href="TextWidgetObjects.html" title="Multiline Text Editor">
<link rel="chapter" href="TreeWidgetObjects.html" title="Tree, List and Icon Grid Widgets">
<link rel="chapter" href="MenusAndCombos.html" title="Menus, Combo Box, Toolbar">
<link rel="chapter" href="Actions.html" title="Action-based menus and toolbars">
<link rel="chapter" href="SelectorWidgets.html" title="Selectors (File/Font/Color/Input Devices)">
<link rel="chapter" href="LayoutContainers.html" title="Layout Containers">
<link rel="chapter" href="Ornaments.html" title="Ornaments">
<link rel="chapter" href="ScrollingWidgets.html" title="Scrolling">
<link rel="chapter" href="Printing.html" title="Printing">
<link rel="chapter" href="MiscObjects.html" title="Miscellaneous">
<link rel="chapter" href="AbstractObjects.html" title="Abstract Base Classes">
<link rel="chapter" href="PlugSocket.html" title="Cross-process Embedding">
<link rel="chapter" href="SpecialObjects.html" title="Special-purpose features">
<link rel="chapter" href="RecentDocuments.html" title="Recently Used Documents">
<link rel="chapter" href="DeprecatedObjects.html" title="Deprecated">
<link rel="part" href="migrating.html" title="Part IV. Migrating from Previous Versions of GTK+">
<link rel="chapter" href="gtk-migrating-checklist.html" title="Migration Checklist">
<link rel="chapter" href="gtk-migrating-GtkFileChooser.html" title="Migrating from GtkFileSelection to GtkFileChooser">
<link rel="chapter" href="gtk-migrating-GtkAction.html" title="Migrating from old menu and toolbar systems to GtkAction">
<link rel="chapter" href="gtk-migrating-GtkComboBox.html" title="Migrating from GtkOptionMenu and GtkCombo to GtkComboBox and
GtkComboBoxEntry">
<link rel="chapter" href="gtk-migrating-GtkIconView.html" title="Migrating from GnomeIconList to GtkIconView">
<link rel="chapter" href="gtk-migrating-GtkAboutDialog.html" title="Migrating from GnomeAbout to GtkAboutDialog">
<link rel="chapter" href="gtk-migrating-GtkColorButton.html" title="Migrating from GnomeColorPicker to GtkColorButton">
<link rel="chapter" href="gtk-migrating-GtkAssistant.html" title="Migrating from GnomeDruid to GtkAssistant">
<link rel="chapter" href="gtk-migrating-GtkRecentChooser.html" title="Migrating from EggRecent to GtkRecentChooser">
<link rel="chapter" href="gtk-migrating-GtkLinkButton.html" title="Migrating from GnomeHRef to GtkLinkButton">
<link rel="part" href="pt05.html" title="Part V. GTK+ Tools">
<link rel="glossary" href="glossary.html" title="Glossary">
<link rel="index" href="ix01.html" title="Index">
<link rel="index" href="ix02.html" title="Index of deprecated symbols">
<link rel="index" href="ix03.html" title="Index of new symbols in 2.2">
<link rel="index" href="ix04.html" title="Index of new symbols in 2.4">
<link rel="index" href="ix05.html" title="Index of new symbols in 2.6">
<link rel="index" href="ix06.html" title="Index of new symbols in 2.8">
<link rel="index" href="ix07.html" title="Index of new symbols in 2.10">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="2"><tr valign="middle">
<td><a accesskey="p" href="checklist-gdkeventexpose-region.html"><img src="left.png" width="24" height="24" border="0" alt="Prev"></a></td>
<td><a accesskey="u" href="gtk-migrating-checklist.html"><img src="up.png" width="24" height="24" border="0" alt="Up"></a></td>
<td><a accesskey="h" href="index.html"><img src="home.png" width="24" height="24" border="0" alt="Home"></a></td>
<th width="100%" align="center">GTK+ Reference Manual</th>
<td><a accesskey="n" href="checklist-named-icons.html"><img src="right.png" width="24" height="24" border="0" alt="Next"></a></td>
</tr></table>
<div class="section" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="checklist-modifiers"></a>Test for modifier keys correctly</h2></div></div></div>
<p><b>Why. </b>
With
<a href="gtk-Keyboard-Accelerators.html#gtk-accelerator-get-default-mod-mask"><code class="function">gtk_accelerator_get_default_mod_mask()</code></a>
you can test for modifier keys reliably; this way your key
event handlers will work correctly even if
<span><strong class="keycap">NumLock</strong></span> or <span><strong class="keycap">CapsLock</strong></span> are
activated.
</p>
<p>
In a <span class="structname">GdkEventKey</span>, the
<em class="structfield"><code>state</code></em> field is a bit mask which
indicates the modifier state at the time the key was pressed.
Modifiers are keys like <span><strong class="keycap">Control</strong></span> and
<span><strong class="keycap">NumLock</strong></span>. When implementing a <a href="GtkWidget.html#GtkWidget-key-press-event">GtkWidget::key_press_event</a>
handler, you should use <a href="gtk-Keyboard-Accelerators.html#gtk-accelerator-get-default-mod-mask"><code class="function">gtk_accelerator_get_default_mod_mask()</code></a> to
test against modifier keys. This function returns a bit mask
which encompasses all the modifiers which the user may be
actively pressing, such as <span><strong class="keycap">Control</strong></span>,
<span><strong class="keycap">Shift</strong></span>, and <span><strong class="keycap">Alt</strong></span>, but ignores
"inocuous" modifiers such as <span><strong class="keycap">NumLock</strong></span> and
<span><strong class="keycap">CapsLock</strong></span>.
</p>
<p>
Say you want to see if
<span><strong class="keycap">Control</strong></span>-<span><strong class="keycap">F10</strong></span>
was pressed. Doing a simple test like
<code class="literal">event->keysym == GDK_F10 &&
event->state == GDK_CONTROL_MASK</code> is not
enough. If <span><strong class="keycap">CapsLock</strong></span> is pressed, then
<em class="structfield"><code>event->state</code></em> will be equal to
<code class="literal">GDK_CONTROL_MASK | GDK_LOCK_MASK</code>, and the
simple test will fail. By taking the logical-and of
<em class="structfield"><code>event->state</code></em> and
<a href="gtk-Keyboard-Accelerators.html#gtk-accelerator-get-default-mod-mask"><code class="function">gtk_accelerator_get_default_mod_mask()</code></a>, you
can ignore the modifiers which are not actively pressed by the
user at the same time as the base key.
</p>
<p>
The following example correctly tests for
<span><strong class="keycap">Control</strong></span>-<span><strong class="keycap">F10</strong></span>
being pressed.
</p>
<a name="default-mod-mask"></a><pre class="programlisting">
static gboolean
my_widget_key_press_event_handler (GtkWidget *widget, GdkEventKey *event)
{
guint modifiers;
modifiers = gtk_accelerator_get_default_mod_mask ();
if (event->keysym == GDK_F10
&& (event->state & modifiers) == GDK_CONTROL_MASK)
{
g_print ("Control-F10 was pressed\n");
return TRUE;
}
return FALSE;
}
</pre>
</div>
</body>
</html>