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88 lines
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<title>Test for modifier keys correctly: GTK+ 3 Reference Manual</title>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="checklist-modifiers"></a>Test for modifier keys correctly</h2></div></div></div>
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<p><b>Why. </b>
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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
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modifier keys reliably; this way your key event handlers will
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work correctly even if <span class="keycap"><strong>NumLock</strong></span> or
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<span class="keycap"><strong>CapsLock</strong></span> are activated.
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</p>
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<p>
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In a <span class="structname">GdkEventKey</span>, the
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<em class="structfield"><code>state</code></em> field is a bit mask which
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indicates the modifier state at the time the key was pressed.
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Modifiers are keys like <span class="keycap"><strong>Control</strong></span> and
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<span class="keycap"><strong>NumLock</strong></span>. When implementing a
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<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
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<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
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test against modifier keys. This function returns a bit mask
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which encompasses all the modifiers which the user may be
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actively pressing, such as <span class="keycap"><strong>Control</strong></span>,
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<span class="keycap"><strong>Shift</strong></span>, and <span class="keycap"><strong>Alt</strong></span>, but ignores
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"innocuous" modifiers such as <span class="keycap"><strong>NumLock</strong></span> and
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<span class="keycap"><strong>CapsLock</strong></span>.
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</p>
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<p>
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Say you want to see if
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<span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>F10</strong></span>
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was pressed. Doing a simple test like
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<code class="literal">event->keysym == GDK_F10 &&
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event->state == GDK_CONTROL_MASK</code> is not
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enough. If <span class="keycap"><strong>CapsLock</strong></span> is pressed, then
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<em class="structfield"><code>event->state</code></em> will be equal to
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<code class="literal">GDK_CONTROL_MASK | GDK_LOCK_MASK</code>, and the
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simple test will fail. By taking the logical-and of
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<em class="structfield"><code>event->state</code></em> and
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<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
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can ignore the modifiers which are not actively pressed by the
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user at the same time as the base key.
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</p>
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<p>
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The following example correctly tests for
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<span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>F10</strong></span>
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being pressed.
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</p>
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<a name="default-mod-mask"></a><pre class="programlisting">
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static gboolean
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my_widget_key_press_event_handler (GtkWidget *widget, GdkEventKey *event)
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{
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GdkModifierType modifiers;
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modifiers = gtk_accelerator_get_default_mod_mask ();
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if (event->keysym == GDK_F10
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&& (event->state & modifiers) == GDK_CONTROL_MASK)
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{
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g_print ("Control-F10 was pressed\n");
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return TRUE;
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}
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return FALSE;
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}
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</pre>
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