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| <div class="sect1"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="howto-interface-implement"></a>Implementing interfaces</h2></div></div></div> |
| <p> |
| Once the interface is defined, implementing it is rather trivial. |
| </p> |
| <p> |
| The first step is to define a normal final GObject class exactly as in |
| <a class="xref" href="howto-gobject.html#howto-gobject-header" title="Boilerplate header code">the section called “Boilerplate header code”</a>. |
| </p> |
| <p> |
| The second step is to implement <span class="type">ViewerFile</span> by defining |
| it using |
| <code class="function"><a class="link" href="gobject-Type-Information.html#G-DEFINE-TYPE-WITH-CODE:CAPS" title="G_DEFINE_TYPE_WITH_CODE()">G_DEFINE_TYPE_WITH_CODE</a></code> |
| and |
| <code class="function"><a class="link" href="gobject-Type-Information.html#G-IMPLEMENT-INTERFACE:CAPS" title="G_IMPLEMENT_INTERFACE()">G_IMPLEMENT_INTERFACE</a></code> |
| instead of |
| <code class="function"><a class="link" href="gobject-Type-Information.html#G-DEFINE-TYPE:CAPS" title="G_DEFINE_TYPE()">G_DEFINE_TYPE</a></code>: |
| </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 |
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| 5</pre></td> |
| <td class="listing_code"><pre class="programlisting"><span class="keyword">static</span><span class="normal"> </span><span class="type">void</span><span class="normal"> </span><span class="function">viewer_file_editable_interface_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="function"><a href="gobject-Type-Information.html#G-DEFINE-TYPE-WITH-CODE:CAPS">G_DEFINE_TYPE_WITH_CODE</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> |
| <span class="normal"> </span><span class="function"><a href="gobject-Type-Information.html#G-IMPLEMENT-INTERFACE:CAPS">G_IMPLEMENT_INTERFACE</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">VIEWER_TYPE_EDITABLE</span><span class="symbol">,</span> |
| <span class="normal"> viewer_file_editable_interface_init</span><span class="symbol">))</span></pre></td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| |
| <p> |
| This definition is very much like all the similar functions seen |
| previously. The only interface-specific code present here is the use of |
| <code class="function"><a class="link" href="gobject-Type-Information.html#G-IMPLEMENT-INTERFACE:CAPS" title="G_IMPLEMENT_INTERFACE()">G_IMPLEMENT_INTERFACE</a></code>. |
| </p> |
| <div class="note"><p>Classes can implement multiple interfaces by using multiple calls to |
| <code class="function"><a class="link" href="gobject-Type-Information.html#G-IMPLEMENT-INTERFACE:CAPS" title="G_IMPLEMENT_INTERFACE()">G_IMPLEMENT_INTERFACE</a></code> |
| inside the call to |
| <code class="function"><a class="link" href="gobject-Type-Information.html#G-DEFINE-TYPE-WITH-CODE:CAPS" title="G_DEFINE_TYPE_WITH_CODE()">G_DEFINE_TYPE_WITH_CODE</a></code> |
| </p></div> |
| <p> |
| <code class="function">viewer_file_editable_interface_init</code>, the interface |
| initialization function: inside it every virtual method of the interface |
| must be assigned to its implementation: |
| </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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| 37</pre></td> |
| <td class="listing_code"><pre class="programlisting"><span class="keyword">static</span><span class="normal"> </span><span class="type">void</span> |
| <span class="function">viewer_file_editable_save</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerFile</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="function"><a href="../glib-Warnings-and-Assertions.html#g-print">g_print</a></span><span class="normal"> </span><span class="symbol">(</span><span class="string">"File implementation of editable interface save method: %s.</span><span class="specialchar">\n</span><span class="string">"</span><span class="symbol">,</span> |
| <span class="normal"> self</span><span class="symbol">-></span><span class="normal">filename</span><span class="symbol">);</span> |
| <span class="cbracket">}</span> |
| |
| <span class="keyword">static</span><span class="normal"> </span><span class="type">void</span> |
| <span class="function">viewer_file_editable_undo</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerFile</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="function"><a href="../glib-Warnings-and-Assertions.html#g-print">g_print</a></span><span class="normal"> </span><span class="symbol">(</span><span class="string">"File implementation of editable interface undo method: %s.</span><span class="specialchar">\n</span><span class="string">"</span><span class="symbol">,</span> |
| <span class="normal"> self</span><span class="symbol">-></span><span class="normal">filename</span><span class="symbol">);</span> |
| <span class="cbracket">}</span> |
| |
| <span class="keyword">static</span><span class="normal"> </span><span class="type">void</span> |
| <span class="function">viewer_file_editable_redo</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerFile</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="function"><a href="../glib-Warnings-and-Assertions.html#g-print">g_print</a></span><span class="normal"> </span><span class="symbol">(</span><span class="string">"File implementation of editable interface redo method: %s.</span><span class="specialchar">\n</span><span class="string">"</span><span class="symbol">,</span> |
| <span class="normal"> self</span><span class="symbol">-></span><span class="normal">filename</span><span class="symbol">);</span> |
| <span class="cbracket">}</span> |
| |
| <span class="keyword">static</span><span class="normal"> </span><span class="type">void</span> |
| <span class="function">viewer_file_editable_interface_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"> iface</span><span class="symbol">-></span><span class="normal">save </span><span class="symbol">=</span><span class="normal"> viewer_file_editable_save</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"> viewer_file_editable_undo</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"> viewer_file_editable_redo</span><span class="symbol">;</span> |
| <span class="cbracket">}</span> |
| |
| <span class="keyword">static</span><span class="normal"> </span><span class="type">void</span> |
| <span class="function">viewer_file_init</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">ViewerFile</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">self</span><span class="symbol">)</span> |
| <span class="cbracket">{</span> |
| <span class="normal"> </span><span class="comment">/* Instance variable initialisation code. */</span> |
| <span class="cbracket">}</span></pre></td> |
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