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Breadcrumbs go here --> <li><a href="all-examples.html">Examples</a></li> <li>QML Examples & Demos</li> <li>Chapter 6: Writing an Extension Plugin</li> </ul> </div> <div class="toolbuttons toolblock"> <ul> <li id="smallA" class="t_button">A</li> <li id="medA" class="t_button active">A</li> <li id="bigA" class="t_button">A</li> <li id="print" class="t_button"><a href="javascript:this.print();"> <span>Print</span></a></li> </ul> </div> </div> <div class="content mainContent"> <h1 class="title">Chapter 6: Writing an Extension Plugin</h1> <span class="subtitle"></span> <!-- $$$declarative/tutorials/extending/chapter6-plugins-description --> <div class="descr"> <a name="details"></a> <p>Files:</p> <ul> <li><a href="declarative-tutorials-extending-chapter6-plugins-app-qml.html">declarative/tutorials/extending/chapter6-plugins/app.qml</a></li> <li><a href="declarative-tutorials-extending-chapter6-plugins-chartsplugin-cpp.html">declarative/tutorials/extending/chapter6-plugins/chartsplugin.cpp</a></li> <li><a href="declarative-tutorials-extending-chapter6-plugins-chartsplugin-h.html">declarative/tutorials/extending/chapter6-plugins/chartsplugin.h</a></li> <li><a href="declarative-tutorials-extending-chapter6-plugins-piechart-cpp.html">declarative/tutorials/extending/chapter6-plugins/piechart.cpp</a></li> <li><a href="declarative-tutorials-extending-chapter6-plugins-piechart-h.html">declarative/tutorials/extending/chapter6-plugins/piechart.h</a></li> <li><a href="declarative-tutorials-extending-chapter6-plugins-pieslice-cpp.html">declarative/tutorials/extending/chapter6-plugins/pieslice.cpp</a></li> <li><a href="declarative-tutorials-extending-chapter6-plugins-pieslice-h.html">declarative/tutorials/extending/chapter6-plugins/pieslice.h</a></li> <li><a href="declarative-tutorials-extending-chapter6-plugins-chapter6-plugins-pro.html">declarative/tutorials/extending/chapter6-plugins/chapter6-plugins.pro</a></li> <li><a href="declarative-tutorials-extending-chapter6-plugins-qmldir.html">declarative/tutorials/extending/chapter6-plugins/qmldir</a></li> </ul> <p>Currently the <tt>PieChart</tt> and <tt>PieSlice</tt> types are used by <tt>app.qml</tt>, which is displayed using a <a href="qdeclarativeview.html">QDeclarativeView</a> in a C++ application. An alternative way to use our QML extension is to create a plugin library to make it available to the QML engine. This allows <tt>app.qml</tt> to be loaded with the <a href="qmlviewer.html">QML Viewer</a> (or some other QML <a href="qmlruntime.html">runtime</a> application) instead of writing a <tt>main.cpp</tt> file and loading our own C++ application.</p> <p>To create a plugin library, we need:</p> <ul> <li>A plugin class that registers our QML types</li> <li>A project file that describes the plugin</li> <li>A <a href="qdeclarativemodules.html#writing-a-qmldir-file">qmldir</a> file that tells the QML engine to load the plugin</li> </ul> <p>First, we create a plugin class named <tt>ChartsPlugin</tt>. It subclasses <a href="qdeclarativeextensionplugin.html">QDeclarativeExtensionPlugin</a> and registers our QML types in the inherited <a href="qdeclarativeextensionplugin.html#registerTypes">registerTypes()</a> method. It also calls <a href="qtplugin.html#Q_EXPORT_PLUGIN2#q-export-plugin2">Q_EXPORT_PLUGIN2</a> for Qt's <a href="plugins-howto.html">plugin system</a>.</p> <p>Here is the <tt>ChartsPlugin</tt> definition in <tt>chartsplugin.h</tt>:</p> <pre class="cpp"> <span class="preprocessor">#include <QDeclarativeExtensionPlugin></span> <span class="keyword">class</span> ChartsPlugin : <span class="keyword">public</span> <span class="type"><a href="qdeclarativeextensionplugin.html">QDeclarativeExtensionPlugin</a></span> { Q_OBJECT <span class="keyword">public</span>: <span class="type">void</span> registerTypes(<span class="keyword">const</span> <span class="type">char</span> <span class="operator">*</span>uri); };</pre> <p>And its implementation in <tt>chartsplugin.cpp</tt>:</p> <pre class="cpp"> <span class="preprocessor">#include "piechart.h"</span> <span class="preprocessor">#include "pieslice.h"</span> <span class="preprocessor">#include <qdeclarative.h></span> <span class="type">void</span> ChartsPlugin<span class="operator">::</span>registerTypes(<span class="keyword">const</span> <span class="type">char</span> <span class="operator">*</span>uri) { qmlRegisterType<span class="operator"><</span>PieChart<span class="operator">></span>(uri<span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="string">"PieChart"</span>); qmlRegisterType<span class="operator"><</span>PieSlice<span class="operator">></span>(uri<span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="string">"PieSlice"</span>); } <a href="qtplugin.html#Q_EXPORT_PLUGIN2">Q_EXPORT_PLUGIN2</a>(chartsplugin<span class="operator">,</span> ChartsPlugin);</pre> <p>Then, we write a <tt>.pro</tt> project file that defines the project as a plugin library and specifies with DESTDIR that library files should be built into a "lib" subdirectory:</p> <pre class="cpp"> TEMPLATE = lib CONFIG += qt plugin QT += declarative DESTDIR = lib OBJECTS_DIR = tmp MOC_DIR = tmp HEADERS += piechart.h \ pieslice.h \ chartsplugin.h SOURCES += piechart.cpp \ pieslice.cpp \ chartsplugin.cpp symbian { include($$QT_SOURCE_TREE/examples/symbianpkgrules.pri) TARGET.EPOCALLOWDLLDATA = 1 } maemo5: include($$QT_SOURCE_TREE/examples/maemo5pkgrules.pri)</pre> <p>Finally, we add a <a href="qdeclarativemodules.html#writing-a-qmldir-file">qmldir</a> file that is automatically parsed by the QML engine. In this file, we specify that a plugin named "chapter6-plugin" (the name of the example project) can be found in the "lib" subdirectory:</p> <pre class="cpp"> plugin chapter6<span class="operator">-</span>plugins lib</pre> <p>Now we have a plugin, and instead of having a main.cpp and an executable, we can build the project and then load the QML file in the <a href="qmlviewer.html">QML Viewer</a>:</p> <pre class="cpp"> qmlviewer app<span class="operator">.</span>qml</pre> <p>(On Mac OS X, you can launch the "QMLViewer" application instead.)</p> <p>Notice the "import Charts 1.0" statement has disappeared from <tt>app.qml</tt>. This is because the <tt>qmldir</tt> file is in the same directory as <tt>app.qml</tt>: this is equivalent to having PieChart.qml and PieSlice.qml files inside the project directory, which could both be used by <tt>app.qml</tt> without import statements.</p> </div> <!-- @@@declarative/tutorials/extending/chapter6-plugins --> </div> </div> </div> <div class="ft"> <span></span> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2013 Digia Plc and/or its subsidiaries. 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