glib/docs/reference/gobject/html/howto-gobject-code.html - nest-cam/4320010/glib - Git at Google

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 <div class="sect1">
 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 <a name="howto-gobject-code"></a>Boilerplate code</h2></div></div></div>
 <p>
       In your code, the first step is to <code class="function">#include</code> the
       needed headers:
 </p>
 <div class="informalexample">
   <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
     <tbody>
       <tr>
         <td class="listing_lines" align="right"><pre>1
 2
 3
 4
 5
 6
 7
 8
 9
 10
 11
 12
 13
 14
 15</pre></td>
         <td class="listing_code"><pre class="programlisting"><span class="comment">/*</span>
 <span class="comment"> * Copyright information</span>
 <span class="comment"> */</span>

 <span class="preproc">#include</span><span class="normal"> </span><span class="string">"viewer-file.h"</span>

 <span class="comment">/* Private structure definition. */</span>
 <span class="keyword">typedef</span><span class="normal"> </span><span class="keyword">struct</span><span class="normal"> </span><span class="cbracket">{</span>
 <span class="normal">  </span><span class="usertype">gchar</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">filename</span><span class="symbol">;</span>
 <span class="normal">  </span><span class="comment">/* stuff */</span>
 <span class="cbracket">}</span><span class="normal"> ViewerFilePrivate</span><span class="symbol">;</span>

 <span class="comment">/* </span>
 <span class="comment"> * forward definitions</span>
 <span class="comment"> */</span></pre></td>
       </tr>
     </tbody>
   </table>
 </div>

 <p>
     </p>
 <p>
       If the class is being declared as final using
       <code class="function">G_DECLARE_FINAL_TYPE</code>, its instance structure should
       be defined in the C file:
 </p>
 <div class="informalexample">
   <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
     <tbody>
       <tr>
         <td class="listing_lines" align="right"><pre>1
 2
 3
 4
 5
 6</pre></td>
         <td class="listing_code"><pre class="programlisting"><span class="keyword">struct</span><span class="normal"> </span><span class="classname">_ViewerFile</span>
 <span class="cbracket">{</span>
 <span class="normal">  </span><span class="usertype">GObject</span><span class="normal"> parent_instance</span><span class="symbol">;</span>

 <span class="normal">  </span><span class="comment">/* Other members, including private data. */</span>
 <span class="cbracket">}</span></pre></td>
       </tr>
     </tbody>
   </table>
 </div>

 <p>
     </p>
 <p>
       Call the <code class="function">G_DEFINE_TYPE</code> macro (or
       <code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code> if your class needs
       private data — final types do <span class="emphasis"><em>not</em></span> need private data)
       using the name
       of the type, the prefix of the functions and the parent GType to
       reduce the amount of boilerplate needed. This macro will:

       </p>
 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 <li class="listitem">implement the <code class="function">viewer_file_get_type</code>
         function</li>
 <li class="listitem">define a parent class pointer accessible from
         the whole .c file</li>
 <li class="listitem">add private instance data to the type (if using
         <code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code>)</li>
 </ul></div>
 <p>
     </p>
 <p>
       If the class has been declared as final using
       <code class="function">G_DECLARE_FINAL_TYPE</code> (see
       <a class="xref" href="howto-gobject.html#howto-gobject-header" title="Boilerplate header code">the section called “Boilerplate header code”</a>), private data should be placed in
       the instance structure, <span class="type">ViewerFile</span>, and
       <code class="function">G_DEFINE_TYPE</code> should be used instead of
       <code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code>. The instance structure
       for a final class is not exposed publicly, and is not embedded in the
       instance structures of any derived classes (because the class is final);
       so its size can vary without causing incompatibilities for code which uses
       the class. Conversely, private data for derivable classes
       <span class="emphasis"><em>must</em></span> be included in a private structure, and
       <code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code> must be used.

 </p>
 <div class="informalexample">
   <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
     <tbody>
       <tr>
         <td class="listing_lines" align="right"><pre>1</pre></td>
         <td class="listing_code"><pre class="programlisting"><span class="function"><a href="gobject-Type-Information.html#G-DEFINE-TYPE:CAPS">G_DEFINE_TYPE</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">ViewerFile</span><span class="symbol">,</span><span class="normal"> viewer_file</span><span class="symbol">,</span><span class="normal"> <a href="gobject-Type-Information.html#G-TYPE-OBJECT:CAPS">G_TYPE_OBJECT</a></span><span class="symbol">)</span></pre></td>
       </tr>
     </tbody>
   </table>
 </div>

 <p>
 or
 </p>
 <div class="informalexample">
   <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
     <tbody>
       <tr>
         <td class="listing_lines" align="right"><pre>1</pre></td>
         <td class="listing_code"><pre class="programlisting"><span class="function"><a href="gobject-Type-Information.html#G-DEFINE-TYPE-WITH-PRIVATE:CAPS">G_DEFINE_TYPE_WITH_PRIVATE</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">ViewerFile</span><span class="symbol">,</span><span class="normal"> viewer_file</span><span class="symbol">,</span><span class="normal"> <a href="gobject-Type-Information.html#G-TYPE-OBJECT:CAPS">G_TYPE_OBJECT</a></span><span class="symbol">)</span></pre></td>
       </tr>
     </tbody>
   </table>
 </div>

 <p>
     </p>
 <p>
       It is also possible to use the
       <code class="function">G_DEFINE_TYPE_WITH_CODE</code> macro to control the
       <code class="function">get_type</code> function implementation — for instance, to
       add a call to the <code class="function">G_IMPLEMENT_INTERFACE</code> macro to
       implement an interface.
     </p>
 </div>
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	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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	<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
	<link rel="home" href="index.html" title="GObject Reference Manual">
	<link rel="up" href="howto-gobject.html" title="How to define and implement a new GObject">
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	<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="howto-gobject.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td>
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	</tr></table>
	<div class="sect1">
	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
	<a name="howto-gobject-code"></a>Boilerplate code</h2></div></div></div>
	<p>
	In your code, the first step is to <code class="function">#include</code> the
	needed headers:
	</p>
	<div class="informalexample">
	<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
	<tbody>
	<tr>
	<td class="listing_lines" align="right"><pre>1
	2
	3
	4
	5
	6
	7
	8
	9
	10
	11
	12
	13
	14
	15</pre></td>
	<td class="listing_code"><pre class="programlisting"><span class="comment">/*</span>
	<span class="comment"> * Copyright information</span>
	<span class="comment"> */</span>

	<span class="preproc">#include</span><span class="normal"> </span><span class="string">"viewer-file.h"</span>

	<span class="comment">/* Private structure definition. */</span>
	<span class="keyword">typedef</span><span class="normal"> </span><span class="keyword">struct</span><span class="normal"> </span><span class="cbracket">{</span>
	<span class="normal"> </span><span class="usertype">gchar</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">filename</span><span class="symbol">;</span>
	<span class="normal"> </span><span class="comment">/* stuff */</span>
	<span class="cbracket">}</span><span class="normal"> ViewerFilePrivate</span><span class="symbol">;</span>

	<span class="comment">/* </span>
	<span class="comment"> * forward definitions</span>
	<span class="comment"> */</span></pre></td>
	</tr>
	</tbody>
	</table>
	</div>

	<p>
	</p>
	<p>
	If the class is being declared as final using
	<code class="function">G_DECLARE_FINAL_TYPE</code>, its instance structure should
	be defined in the C file:
	</p>
	<div class="informalexample">
	<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
	<tbody>
	<tr>
	<td class="listing_lines" align="right"><pre>1
	2
	3
	4
	5
	6</pre></td>
	<td class="listing_code"><pre class="programlisting"><span class="keyword">struct</span><span class="normal"> </span><span class="classname">_ViewerFile</span>
	<span class="cbracket">{</span>
	<span class="normal"> </span><span class="usertype">GObject</span><span class="normal"> parent_instance</span><span class="symbol">;</span>

	<span class="normal"> </span><span class="comment">/* Other members, including private data. */</span>
	<span class="cbracket">}</span></pre></td>
	</tr>
	</tbody>
	</table>
	</div>

	<p>
	</p>
	<p>
	Call the <code class="function">G_DEFINE_TYPE</code> macro (or
	<code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code> if your class needs
	private data — final types do <span class="emphasis"><em>not</em></span> need private data)
	using the name
	of the type, the prefix of the functions and the parent GType to
	reduce the amount of boilerplate needed. This macro will:

	</p>
	<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
	<li class="listitem">implement the <code class="function">viewer_file_get_type</code>
	function</li>
	<li class="listitem">define a parent class pointer accessible from
	the whole .c file</li>
	<li class="listitem">add private instance data to the type (if using
	<code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code>)</li>
	</ul></div>
	<p>
	</p>
	<p>
	If the class has been declared as final using
	<code class="function">G_DECLARE_FINAL_TYPE</code> (see
	<a class="xref" href="howto-gobject.html#howto-gobject-header" title="Boilerplate header code">the section called “Boilerplate header code”</a>), private data should be placed in
	the instance structure, <span class="type">ViewerFile</span>, and
	<code class="function">G_DEFINE_TYPE</code> should be used instead of
	<code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code>. The instance structure
	for a final class is not exposed publicly, and is not embedded in the
	instance structures of any derived classes (because the class is final);
	so its size can vary without causing incompatibilities for code which uses
	the class. Conversely, private data for derivable classes
	<span class="emphasis"><em>must</em></span> be included in a private structure, and
	<code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code> must be used.

	</p>
	<div class="informalexample">
	<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
	<tbody>
	<tr>
	<td class="listing_lines" align="right"><pre>1</pre></td>
	<td class="listing_code"><pre class="programlisting"><span class="function"><a href="gobject-Type-Information.html#G-DEFINE-TYPE:CAPS">G_DEFINE_TYPE</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">ViewerFile</span><span class="symbol">,</span><span class="normal"> viewer_file</span><span class="symbol">,</span><span class="normal"> <a href="gobject-Type-Information.html#G-TYPE-OBJECT:CAPS">G_TYPE_OBJECT</a></span><span class="symbol">)</span></pre></td>
	</tr>
	</tbody>
	</table>
	</div>

	<p>
	or
	</p>
	<div class="informalexample">
	<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
	<tbody>
	<tr>
	<td class="listing_lines" align="right"><pre>1</pre></td>
	<td class="listing_code"><pre class="programlisting"><span class="function"><a href="gobject-Type-Information.html#G-DEFINE-TYPE-WITH-PRIVATE:CAPS">G_DEFINE_TYPE_WITH_PRIVATE</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">ViewerFile</span><span class="symbol">,</span><span class="normal"> viewer_file</span><span class="symbol">,</span><span class="normal"> <a href="gobject-Type-Information.html#G-TYPE-OBJECT:CAPS">G_TYPE_OBJECT</a></span><span class="symbol">)</span></pre></td>
	</tr>
	</tbody>
	</table>
	</div>

	<p>
	</p>
	<p>
	It is also possible to use the
	<code class="function">G_DEFINE_TYPE_WITH_CODE</code> macro to control the
	<code class="function">get_type</code> function implementation — for instance, to
	add a call to the <code class="function">G_IMPLEMENT_INTERFACE</code> macro to
	implement an interface.
	</p>
	</div>
	<div class="footer">
	<hr>Generated by GTK-Doc V1.25.1</div>
	</body>
	</html>