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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Test for modifier keys correctly: GTK+ 3 Reference Manual</title> <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> <link rel="home" href="index.html" title="GTK+ 3 Reference Manual"> <link rel="up" href="gtk-migrating-checklist.html" title="Migration Details 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 V1.32 (XML mode)"> <link rel="stylesheet" href="style.css" type="text/css"> </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="5"><tr valign="middle"> <td width="100%" align="left" class="shortcuts"></td> <td><a accesskey="h" href="index.html"><img src="home.png" width="16" height="16" border="0" alt="Home"></a></td> <td><a accesskey="u" href="gtk-migrating-checklist.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td> <td><a accesskey="p" href="checklist-gdkeventexpose-region.html"><img src="left.png" width="16" height="16" border="0" alt="Prev"></a></td> <td><a accesskey="n" href="checklist-named-icons.html"><img src="right.png" width="16" height="16" border="0" alt="Next"></a></td> </tr></table> <div class="section"> <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 class="link" href="gtk3-Keyboard-Accelerators.html#gtk-accelerator-get-default-mod-mask" title="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 class="keycap"><strong>NumLock</strong></span> or <span class="keycap"><strong>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 class="keycap"><strong>Control</strong></span> and <span class="keycap"><strong>NumLock</strong></span>. When implementing a <a class="link" href="GtkWidget.html#GtkWidget-key-press-event" title="The “key-press-event” signal"><span class="type">“key-press-event”</span></a> handler, you should use <a class="link" href="gtk3-Keyboard-Accelerators.html#gtk-accelerator-get-default-mod-mask" title="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 class="keycap"><strong>Control</strong></span>, <span class="keycap"><strong>Shift</strong></span>, and <span class="keycap"><strong>Alt</strong></span>, but ignores "innocuous" modifiers such as <span class="keycap"><strong>NumLock</strong></span> and <span class="keycap"><strong>CapsLock</strong></span>. </p> <p> Say you want to see if <span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>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 class="keycap"><strong>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 class="link" href="gtk3-Keyboard-Accelerators.html#gtk-accelerator-get-default-mod-mask" title="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 class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>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) { GdkModifierType 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> <div class="footer"> <hr>Generated by GTK-Doc V1.32</div> </body> </html>