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| <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 two 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 |
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| 36</pre></td> |
| <td class="listing_code"><pre class="programlisting"><span class="comment">/*</span> |
| <span class="comment"> * Copyright/Licensing information.</span> |
| <span class="comment"> */</span> |
| |
| <span class="preproc">#ifndef</span><span class="normal"> __VIEWER_EDITABLE_H__</span> |
| <span class="preproc">#define</span><span class="normal"> __VIEWER_EDITABLE_H__</span> |
| |
| <span class="preproc">#include</span><span class="normal"> </span><span class="string"><glib-object.h></span> |
| |
| <span class="normal"><a href="../glib-Miscellaneous-Macros.html#G-BEGIN-DECLS:CAPS">G_BEGIN_DECLS</a></span> |
| |
| <span class="preproc">#define</span><span class="normal"> </span><span class="usertype">VIEWER_TYPE_EDITABLE</span><span class="normal"> </span><span class="function">viewer_editable_get_type</span><span class="normal"> </span><span class="symbol">()</span> |
| <span class="function"><a href="gobject-Type-Information.html#G-DECLARE-INTERFACE:CAPS">G_DECLARE_INTERFACE</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">ViewerEditable</span><span class="symbol">,</span><span class="normal"> viewer_editable</span><span class="symbol">,</span><span class="normal"> VIEWER</span><span class="symbol">,</span><span class="normal"> EDITABLE</span><span class="symbol">,</span><span class="normal"> <a href="gobject-The-Base-Object-Type.html#GObject-struct">GObject</a></span><span class="symbol">)</span> |
| |
| <span class="keyword">struct</span><span class="normal"> </span><span class="classname">_ViewerEditableInterface</span> |
| <span class="cbracket">{</span> |
| <span class="normal"> </span><span class="usertype">GTypeInterface</span><span class="normal"> parent_iface</span><span class="symbol">;</span> |
| |
| <span class="normal"> </span><span class="type">void</span><span class="normal"> </span><span class="symbol">(*</span><span class="normal">save</span><span class="symbol">)</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditable</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">,</span> |
| <span class="normal"> </span><span class="usertype">GError</span><span class="normal"> </span><span class="symbol">**</span><span class="normal">error</span><span class="symbol">);</span> |
| <span class="normal"> </span><span class="type">void</span><span class="normal"> </span><span class="symbol">(*</span><span class="normal">undo</span><span class="symbol">)</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditable</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">,</span> |
| <span class="normal"> </span><span class="usertype">guint</span><span class="normal"> n_steps</span><span class="symbol">);</span> |
| <span class="normal"> </span><span class="type">void</span><span class="normal"> </span><span class="symbol">(*</span><span class="normal">redo</span><span class="symbol">)</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditable</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">,</span> |
| <span class="normal"> </span><span class="usertype">guint</span><span class="normal"> n_steps</span><span class="symbol">);</span> |
| <span class="cbracket">}</span><span class="symbol">;</span> |
| |
| <span class="type">void</span><span class="normal"> </span><span class="function">viewer_editable_save</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditable</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">,</span> |
| <span class="normal"> </span><span class="usertype">GError</span><span class="normal"> </span><span class="symbol">**</span><span class="normal">error</span><span class="symbol">);</span> |
| <span class="type">void</span><span class="normal"> </span><span class="function">viewer_editable_undo</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditable</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">,</span> |
| <span class="normal"> </span><span class="usertype">guint</span><span class="normal"> n_steps</span><span class="symbol">);</span> |
| <span class="type">void</span><span class="normal"> </span><span class="function">viewer_editable_redo</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditable</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">,</span> |
| <span class="normal"> </span><span class="usertype">guint</span><span class="normal"> n_steps</span><span class="symbol">);</span> |
| |
| <span class="normal"><a href="../glib-Miscellaneous-Macros.html#G-END-DECLS:CAPS">G_END_DECLS</a></span> |
| |
| <span class="preproc">#endif</span><span class="normal"> </span><span class="comment">/* __VIEWER_EDITABLE_H__ */</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" title="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 |
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| 47</pre></td> |
| <td class="listing_code"><pre class="programlisting"><span class="function"><a href="gobject-Type-Information.html#G-DEFINE-INTERFACE:CAPS">G_DEFINE_INTERFACE</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">ViewerEditable</span><span class="symbol">,</span><span class="normal"> viewer_editable</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> |
| |
| <span class="keyword">static</span><span class="normal"> </span><span class="type">void</span> |
| <span class="function">viewer_editable_default_init</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditableInterface</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">iface</span><span class="symbol">)</span> |
| <span class="cbracket">{</span> |
| <span class="normal"> </span><span class="comment">/* add properties and signals to the interface here */</span> |
| <span class="cbracket">}</span> |
| |
| <span class="type">void</span> |
| <span class="function">viewer_editable_save</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditable</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">,</span> |
| <span class="normal"> </span><span class="usertype">GError</span><span class="normal"> </span><span class="symbol">**</span><span class="normal">error</span><span class="symbol">)</span> |
| <span class="cbracket">{</span> |
| <span class="normal"> </span><span class="usertype">ViewerEditableInterface</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">iface</span><span class="symbol">;</span> |
| |
| <span class="normal"> </span><span class="function"><a href="../glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a></span><span class="normal"> </span><span class="symbol">(</span><span class="function">VIEWER_IS_EDITABLE</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">self</span><span class="symbol">));</span> |
| <span class="normal"> </span><span class="function"><a href="../glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">error </span><span class="symbol">==</span><span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a> </span><span class="symbol">||</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">error </span><span class="symbol">==</span><span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">);</span> |
| |
| <span class="normal"> iface </span><span class="symbol">=</span><span class="normal"> </span><span class="function">VIEWER_EDITABLE_GET_IFACE</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">self</span><span class="symbol">);</span> |
| <span class="normal"> </span><span class="function"><a href="../glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">iface</span><span class="symbol">-></span><span class="normal">save </span><span class="symbol">!=</span><span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">);</span> |
| <span class="normal"> iface</span><span class="symbol">-></span><span class="function">save</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">self</span><span class="symbol">,</span><span class="normal"> error</span><span class="symbol">);</span> |
| <span class="cbracket">}</span> |
| |
| <span class="type">void</span> |
| <span class="function">viewer_editable_undo</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditable</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">,</span> |
| <span class="normal"> </span><span class="usertype">guint</span><span class="normal"> n_steps</span><span class="symbol">)</span> |
| <span class="cbracket">{</span> |
| <span class="normal"> </span><span class="usertype">ViewerEditableInterface</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">iface</span><span class="symbol">;</span> |
| |
| <span class="normal"> </span><span class="function"><a href="../glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a></span><span class="normal"> </span><span class="symbol">(</span><span class="function">VIEWER_IS_EDITABLE</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">self</span><span class="symbol">));</span> |
| |
| <span class="normal"> iface </span><span class="symbol">=</span><span class="normal"> </span><span class="function">VIEWER_EDITABLE_GET_IFACE</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">self</span><span class="symbol">);</span> |
| <span class="normal"> </span><span class="function"><a href="../glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">iface</span><span class="symbol">-></span><span class="normal">undo </span><span class="symbol">!=</span><span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">);</span> |
| <span class="normal"> iface</span><span class="symbol">-></span><span class="function">undo</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">self</span><span class="symbol">,</span><span class="normal"> n_steps</span><span class="symbol">);</span> |
| <span class="cbracket">}</span> |
| |
| <span class="type">void</span> |
| <span class="function">viewer_editable_redo</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerEditable</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">,</span> |
| <span class="normal"> </span><span class="usertype">guint</span><span class="normal"> n_steps</span><span class="symbol">)</span> |
| <span class="cbracket">{</span> |
| <span class="normal"> </span><span class="usertype">ViewerEditableInterface</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">iface</span><span class="symbol">;</span> |
| |
| <span class="normal"> </span><span class="function"><a href="../glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a></span><span class="normal"> </span><span class="symbol">(</span><span class="function">VIEWER_IS_EDITABLE</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">self</span><span class="symbol">));</span> |
| |
| <span class="normal"> iface </span><span class="symbol">=</span><span class="normal"> </span><span class="function">VIEWER_EDITABLE_GET_IFACE</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">self</span><span class="symbol">);</span> |
| <span class="normal"> </span><span class="function"><a href="../glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">iface</span><span class="symbol">-></span><span class="normal">redo </span><span class="symbol">!=</span><span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">);</span> |
| <span class="normal"> iface</span><span class="symbol">-></span><span class="function">redo</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">self</span><span class="symbol">,</span><span class="normal"> n_steps</span><span class="symbol">);</span> |
| <span class="cbracket">}</span></pre></td> |
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