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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="id3003855"></a>How users can abuse signals (and why some think it is good)</h2></div></div></div>
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<p>Now that you know how to create signals to which the users can connect easily and at any point in
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the signal emission process thanks to <code class="function"><a class="link" href="gobject-Signals.html#g-signal-connect">g_signal_connect</a></code>,
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<code class="function"><a class="link" href="gobject-Signals.html#g-signal-connect-after">g_signal_connect_after</a></code> and G_SIGNAL_RUN_LAST, it is time to look into how your
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users can and will screw you. This is also interesting to know how you too, can screw other people.
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This will make you feel good and eleet.
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<div class="itemizedlist"><ul type="disc">
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<li><p>stop the emission of the signal at anytime</p></li>
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<li><p>override the default handler of the signal if it is stored as a function
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pointer in the class structure (which is the preferred way to create a default signal handler,
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as discussed in the previous section).</p></li>
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In both cases, the original programmer should be as careful as possible to write code which is
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resistant to the fact that the default handler of the signal might not able to run. This is obviously
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not the case in the example used in the previous sections since the write to the file depends on whether
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or not the default handler runs (however, this might be your goal: to allow the user to prevent the file
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write if he wishes to).
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If all you want to do is to stop the signal emission from one of the callbacks you connected yourself,
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you can call <code class="function">g_signal_stop_by_name</code>. Its use is very simple which is why I won't detail
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If the signal's default handler is just a class function pointer, it is also possible to override
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it yourself from the class_init function of a type which derives from the parent. That way, when the signal
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is emitted, the parent class will use the function provided by the child as a signal default handler.
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Of course, it is also possible (and recommended) to chain up from the child to the parent's default signal
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handler to ensure the integrity of the parent object.
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Overriding a class method and chaining up was demonstrated in <a class="xref" href="howto-gobject-methods.html" title="Object methods">the section called “Object methods”</a>
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which is why I won't bother to show exactly how to do it here again.
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