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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>How to define and implement interfaces: GObject Reference Manual</title> <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> <link rel="home" href="index.html" title="GObject Reference Manual"> <link rel="up" href="pt02.html" title="Part IV. Tutorial"> <link rel="prev" href="howto-gobject-chainup.html" title="Chaining up"> <link rel="next" href="howto-interface-implement.html" title="Implementing interfaces"> <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="pt02.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td> <td><a accesskey="p" href="howto-gobject-chainup.html"><img src="left.png" width="16" height="16" border="0" alt="Prev"></a></td> <td><a accesskey="n" href="howto-interface-implement.html"><img src="right.png" width="16" height="16" border="0" alt="Next"></a></td> </tr></table> <div class="chapter"> <div class="titlepage"><div><div><h2 class="title"> <a name="howto-interface"></a>How to define and implement interfaces</h2></div></div></div> <div class="toc"><dl class="toc"> <dt><span class="sect1"><a href="howto-interface.html#howto-interface-define">Defining interfaces</a></span></dt> <dt><span class="sect1"><a href="howto-interface-implement.html">Implementing interfaces</a></span></dt> <dt><span class="sect1"><a href="howto-interface-prerequisite.html">Interface definition prerequisites</a></span></dt> <dt><span class="sect1"><a href="howto-interface-properties.html">Interface properties</a></span></dt> <dt><span class="sect1"><a href="howto-interface-override.html">Overriding interface methods</a></span></dt> </dl></div> <div class="sect1"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="howto-interface-define"></a>Defining interfaces</h2></div></div></div> <p> The theory behind how GObject interfaces work is given in <a class="xref" href="gtype-non-instantiable-classed.html" title="Non-instantiable classed types: interfaces">the section called “Non-instantiable classed types: interfaces”</a>; this section covers how to define and implement an interface. </p> <p> The first step is to get the header right. This interface defines three methods: </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 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36</pre></td> <td class="listing_code"><pre class="programlisting"><span class="cm">/*</span> <span class="cm"> * Copyright/Licensing information.</span> <span class="cm"> */</span> <span class="cp">#ifndef __VIEWER_EDITABLE_H__</span> <span class="cp">#define __VIEWER_EDITABLE_H__</span> <span class="cp">#include</span> <span class="cpf"><glib-object.h></span><span class="cp"></span> <span class="n">G_BEGIN_DECLS</span> <span class="cp">#define VIEWER_TYPE_EDITABLE viewer_editable_get_type ()</span> <span class="n">G_DECLARE_INTERFACE</span> <span class="p">(</span><span class="n">ViewerEditable</span><span class="p">,</span> <span class="n">viewer_editable</span><span class="p">,</span> <span class="n">VIEWER</span><span class="p">,</span> <span class="n">EDITABLE</span><span class="p">,</span> <span class="n">GObject</span><span class="p">)</span> <span class="k">struct</span> <span class="n">_ViewerEditableInterface</span> <span class="p">{</span> <span class="n">GTypeInterface</span> <span class="n">parent_iface</span><span class="p">;</span> <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">save</span><span class="p">)</span> <span class="p">(</span><span class="n">ViewerEditable</span> <span class="o">*</span><span class="n">self</span><span class="p">,</span> <span class="n">GError</span> <span class="o">**</span><span class="n">error</span><span class="p">);</span> <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">undo</span><span class="p">)</span> <span class="p">(</span><span class="n">ViewerEditable</span> <span class="o">*</span><span class="n">self</span><span class="p">,</span> <span class="n">guint</span> <span class="n">n_steps</span><span class="p">);</span> <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">redo</span><span class="p">)</span> <span class="p">(</span><span class="n">ViewerEditable</span> <span class="o">*</span><span class="n">self</span><span class="p">,</span> <span class="n">guint</span> <span class="n">n_steps</span><span class="p">);</span> <span class="p">};</span> <span class="kt">void</span> <span class="nf">viewer_editable_save</span> <span class="p">(</span><span class="n">ViewerEditable</span> <span class="o">*</span><span class="n">self</span><span class="p">,</span> <span class="n">GError</span> <span class="o">**</span><span class="n">error</span><span class="p">);</span> <span class="kt">void</span> <span class="nf">viewer_editable_undo</span> <span class="p">(</span><span class="n">ViewerEditable</span> <span class="o">*</span><span class="n">self</span><span class="p">,</span> <span class="n">guint</span> <span class="n">n_steps</span><span class="p">);</span> <span class="kt">void</span> <span class="nf">viewer_editable_redo</span> <span class="p">(</span><span class="n">ViewerEditable</span> <span class="o">*</span><span class="n">self</span><span class="p">,</span> <span class="n">guint</span> <span class="n">n_steps</span><span class="p">);</span> <span class="n">G_END_DECLS</span> <span class="cp">#endif </span><span class="cm">/* __VIEWER_EDITABLE_H__ */</span><span class="cp"></span></pre></td> </tr> </tbody> </table> </div> <p> This code is the same as the code for a normal <a class="link" href="gobject-Type-Information.html#GType"><span class="type">GType</span></a> which derives from a <a class="link" href="gobject-The-Base-Object-Type.html#GObject"><span class="type">GObject</span></a> except for a few details: </p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"><p> The <code class="function">_GET_CLASS</code> function is called <code class="function">_GET_IFACE</code> (and is defined by <a class="link" href="gobject-Type-Information.html#G-DECLARE-INTERFACE:CAPS" title="G_DECLARE_INTERFACE()"><code class="function">G_DECLARE_INTERFACE</code></a>). </p></li> <li class="listitem"><p> The instance type, <span class="type">ViewerEditable</span>, is not fully defined: it is used merely as an abstract type which represents an instance of whatever object which implements the interface. </p></li> <li class="listitem"><p> The parent of the <span class="type">ViewerEditableInterface</span> is <span class="type">GTypeInterface</span>, not <span class="type">GObjectClass</span>. </p></li> </ul></div> <p> </p> <p> The implementation of the <span class="type">ViewerEditable</span> type itself is trivial: </p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"><p><code class="function"><a class="link" href="gobject-Type-Information.html#G-DEFINE-INTERFACE:CAPS" title="G_DEFINE_INTERFACE()">G_DEFINE_INTERFACE</a></code> creates a <code class="function">viewer_editable_get_type</code> function which registers the type in the type system. The third argument is used to define a <a class="link" href="howto-interface-prerequisite.html" title="Interface definition prerequisites">prerequisite interface</a> (which we'll talk about more later). Just pass <code class="code">0</code> for this argument when an interface has no prerequisite. </p></li> <li class="listitem"><p><code class="function">viewer_editable_default_init</code> is expected to register the interface's signals if there are any (we will see a bit later how to use them).</p></li> <li class="listitem"><p>The interface methods <code class="function">viewer_editable_save</code>, <code class="function">viewer_editable_undo</code> and <code class="function">viewer_editable_redo</code> dereference the interface structure to access its associated interface function and call it. </p></li> </ul></div> <p> </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 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47</pre></td> <td class="listing_code"><pre class="programlisting"><span class="n">G_DEFINE_INTERFACE</span> <span class="p">(</span><span class="n">ViewerEditable</span><span class="p">,</span> <span class="n">viewer_editable</span><span class="p">,</span> <span class="n">G_TYPE_OBJECT</span><span class="p">)</span> <span class="k">static</span> <span class="kt">void</span> <span class="n">viewer_editable_default_init</span> <span class="p">(</span><span class="n">ViewerEditableInterface</span> <span class="o">*</span><span class="n">iface</span><span class="p">)</span> <span class="p">{</span> <span class="cm">/* add properties and signals to the interface here */</span> <span class="p">}</span> <span class="kt">void</span> <span class="n">viewer_editable_save</span> <span class="p">(</span><span class="n">ViewerEditable</span> <span class="o">*</span><span class="n">self</span><span class="p">,</span> <span class="n">GError</span> <span class="o">**</span><span class="n">error</span><span class="p">)</span> <span class="p">{</span> <span class="n">ViewerEditableInterface</span> <span class="o">*</span><span class="n">iface</span><span class="p">;</span> <span class="n">g_return_if_fail</span> <span class="p">(</span><span class="n">VIEWER_IS_EDITABLE</span> <span class="p">(</span><span class="n">self</span><span class="p">));</span> <span class="n">g_return_if_fail</span> <span class="p">(</span><span class="n">error</span> <span class="o">==</span> <span class="nb">NULL</span> <span class="o">||</span> <span class="o">*</span><span class="n">error</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">);</span> <span class="n">iface</span> <span class="o">=</span> <span class="n">VIEWER_EDITABLE_GET_IFACE</span> <span class="p">(</span><span class="n">self</span><span class="p">);</span> <span class="n">g_return_if_fail</span> <span class="p">(</span><span class="n">iface</span><span class="o">-></span><span class="n">save</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">);</span> <span class="n">iface</span><span class="o">-></span><span class="n">save</span> <span class="p">(</span><span class="n">self</span><span class="p">,</span> <span class="n">error</span><span class="p">);</span> <span class="p">}</span> <span class="kt">void</span> <span class="n">viewer_editable_undo</span> <span class="p">(</span><span class="n">ViewerEditable</span> <span class="o">*</span><span class="n">self</span><span class="p">,</span> <span class="n">guint</span> <span class="n">n_steps</span><span class="p">)</span> <span class="p">{</span> <span class="n">ViewerEditableInterface</span> <span class="o">*</span><span class="n">iface</span><span class="p">;</span> <span class="n">g_return_if_fail</span> <span class="p">(</span><span class="n">VIEWER_IS_EDITABLE</span> <span class="p">(</span><span class="n">self</span><span class="p">));</span> <span class="n">iface</span> <span class="o">=</span> <span class="n">VIEWER_EDITABLE_GET_IFACE</span> <span class="p">(</span><span class="n">self</span><span class="p">);</span> <span class="n">g_return_if_fail</span> <span class="p">(</span><span class="n">iface</span><span class="o">-></span><span class="n">undo</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">);</span> <span class="n">iface</span><span class="o">-></span><span class="n">undo</span> <span class="p">(</span><span class="n">self</span><span class="p">,</span> <span class="n">n_steps</span><span class="p">);</span> <span class="p">}</span> <span class="kt">void</span> <span class="n">viewer_editable_redo</span> <span class="p">(</span><span class="n">ViewerEditable</span> <span class="o">*</span><span class="n">self</span><span class="p">,</span> <span class="n">guint</span> <span class="n">n_steps</span><span class="p">)</span> <span class="p">{</span> <span class="n">ViewerEditableInterface</span> <span class="o">*</span><span class="n">iface</span><span class="p">;</span> <span class="n">g_return_if_fail</span> <span class="p">(</span><span class="n">VIEWER_IS_EDITABLE</span> <span class="p">(</span><span class="n">self</span><span class="p">));</span> <span class="n">iface</span> <span class="o">=</span> <span class="n">VIEWER_EDITABLE_GET_IFACE</span> <span class="p">(</span><span class="n">self</span><span class="p">);</span> <span class="n">g_return_if_fail</span> <span class="p">(</span><span class="n">iface</span><span class="o">-></span><span class="n">redo</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">);</span> <span class="n">iface</span><span class="o">-></span><span class="n">redo</span> <span class="p">(</span><span class="n">self</span><span class="p">,</span> <span class="n">n_steps</span><span class="p">);</span> <span class="p">}</span></pre></td> </tr> </tbody> </table> </div> <p> </p> </div> </div> <div class="footer"> <hr>Generated by GTK-Doc V1.32</div> </body> </html>