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<h1 class="title"><QtPlugin> - Defining Plugins</h1>
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<p>The <<a href="../qmake/qmake-variable-reference.html#qtplugin">QtPlugin</a>> header file defines macros for defining plugins. <a href="#details">More...</a></p>
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<a name="Macros"></a>
<h2 id="Macros">Macros</h2>
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<tr><td class="memItemLeft topAlign rightAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qtplugin.html#Q_DECLARE_INTERFACE">Q_DECLARE_INTERFACE</a></b>(<i>ClassName</i>, <i>Identifier</i>)</td></tr>
<tr><td class="memItemLeft topAlign rightAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qtplugin.html#Q_IMPORT_PLUGIN">Q_IMPORT_PLUGIN</a></b>(<i>PluginName</i>)</td></tr>
<tr><td class="memItemLeft topAlign rightAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qtplugin.html#Q_PLUGIN_METADATA">Q_PLUGIN_METADATA</a></b>(<i>...</i>)</td></tr>
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<p><b>See also </b>How to Create Qt Plugins.</p>
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<h2>Macro Documentation</h2>
<!-- $$$Q_DECLARE_INTERFACE[overload1]$$$Q_DECLARE_INTERFACE -->
<h3 class="fn" id="Q_DECLARE_INTERFACE"><a name="Q_DECLARE_INTERFACE"></a><span class="name">Q_DECLARE_INTERFACE</span>(<i>ClassName</i>, <i>Identifier</i>)</h3>
<p>This macro associates the given <i>Identifier</i> (a string literal) to the interface class called <i>ClassName</i>. The <i>Identifier</i> must be unique. For example:</p>
<pre class="cpp">
<span class="preprocessor">#define BrushInterface_iid "org.qt-project.Qt.Examples.PlugAndPaint.BrushInterface"</span>
Q_DECLARE_INTERFACE(BrushInterface<span class="operator">,</span> BrushInterface_iid)
</pre>
<p>This macro is normally used right after the class definition for <i>ClassName</i>, in a header file. See the <a href="../qtwidgets/qtwidgets-tools-plugandpaint-app-example.html">Plug & Paint</a> example for details.</p>
<p>If you want to use Q_DECLARE_INTERFACE with interface classes declared in a namespace then you have to make sure the Q_DECLARE_INTERFACE is not inside a namespace though. For example:</p>
<pre class="cpp">
<span class="keyword">namespace</span> Foo
{
<span class="keyword">struct</span> MyInterface { <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span> };
}
Q_DECLARE_INTERFACE(Foo<span class="operator">::</span>MyInterface<span class="operator">,</span> <span class="string">"org.examples.MyInterface"</span>)
</pre>
<p><b>See also </b><a href="qobject.html#Q_INTERFACES">Q_INTERFACES</a>() and How to Create Qt Plugins.</p>
<!-- @@@Q_DECLARE_INTERFACE -->
<!-- $$$Q_IMPORT_PLUGIN[overload1]$$$Q_IMPORT_PLUGIN -->
<h3 class="fn" id="Q_IMPORT_PLUGIN"><a name="Q_IMPORT_PLUGIN"></a><span class="name">Q_IMPORT_PLUGIN</span>(<i>PluginName</i>)</h3>
<p>This macro imports the plugin named <i>PluginName</i>, which corresponds with the name of the class that declares metadata for the plugin with <a href="qtplugin.html#Q_PLUGIN_METADATA">Q_PLUGIN_METADATA</a>().</p>
<p>Inserting this macro into your application's source code will allow you to make use of a static plugin.</p>
<p>Example:</p>
<pre class="cpp">
Q_IMPORT_PLUGIN(qjpeg)
</pre>
<p>Static plugins must also be included by the linker when your application is built. For Qt's predefined plugins, you can use the <code>QTPLUGIN</code> to add the required plugins to your build. For example:</p>
<pre class="cpp">
TEMPLATE = app
QTPLUGIN += qjpeg qgif # image formats
</pre>
<p><b>See also </b>Static Plugins, How to Create Qt Plugins, and <a href="../qmake/qmake-tutorial.html">Getting Started with qmake</a>.</p>
<!-- @@@Q_IMPORT_PLUGIN -->
<!-- $$$Q_PLUGIN_METADATA[overload1]$$$Q_PLUGIN_METADATA... -->
<h3 class="fn" id="Q_PLUGIN_METADATA"><a name="Q_PLUGIN_METADATA"></a><span class="name">Q_PLUGIN_METADATA</span>(<i>...</i>)</h3>
<p>This macro is being used to declare meta data that is part of a plugin that instantiates this object.</p>
<p>The macro needs to declare the IID of the interface implemented through the object, and reference a file containing the meta data for the plugin.</p>
<p>There should be exactly one occurrence of this macro in the source code for a Qt plugin.</p>
<p>Example:</p>
<pre class="cpp">
<span class="keyword">class</span> MyInstance : <span class="keyword">public</span> <span class="type"><a href="qobject.html">QObject</a></span>
{
Q_PLUGIN_METADATA(IID <span class="string">"org.qt-project.Qt.QDummyPlugin"</span> FILE <span class="string">"mymetadata.json"</span>)
};
</pre>
<p>See the <a href="../qtwidgets/qtwidgets-tools-plugandpaint-app-example.html">Plug & Paint</a> example for details.</p>
<p>Note that the class this macro appears on must be default-constructible.</p>
<p>FILE is optional and points to a json file.</p>
<p>The json file must reside in one of the include directories specified by the build-system. moc exits with an error when it could not find the specified file.</p>
<p>This function was introduced in Qt 5.0.</p>
<p><b>See also </b><a href="qtplugin.html#Q_DECLARE_INTERFACE">Q_DECLARE_INTERFACE</a>() and How to Create Qt Plugins.</p>
<!-- @@@Q_PLUGIN_METADATA -->
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