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<title>Qt 4.8: Qt Declarative UI Runtime</title>
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<a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a>
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<li>Qt Declarative UI Runtime</li>
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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#deploying-qml-based-applications">Deploying QML-based applications</a></li>
<li class="level2"><a href="#deploying-with-qdeclarativeview">Deploying with QDeclarativeView</a></li>
<li class="level2"><a href="#creating-a-qdeclarativeengine-directly">Creating a QDeclarativeEngine directly</a></li>
<li class="level1"><a href="#developing-and-prototyping-with-qml-viewer">Developing and prototyping with QML Viewer</a></li>
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<h1 class="title">Qt Declarative UI Runtime</h1>
<span class="subtitle"></span>
<!-- $$$qmlruntime.html-description -->
<div class="descr"> <a name="details"></a>
<p>QML documents are loaded and executed by the QML runtime. This includes the Declarative UI engine along with the built-in QML elements and plugin modules, and it also provides access to third-party QML elements and modules.</p>
<p>Applications that use QML need to invoke the QML runtime in order to execute QML documents. This can be done by creating a <a href="qdeclarativeview.html">QDeclarativeView</a> or a <a href="qdeclarativeengine.html">QDeclarativeEngine</a>, as described below. In addition, the Declarative UI package includes the <i>Qt QML Viewer</i> tool, which loads <tt>.qml</tt> files. This tool is useful for developing and testing QML code without the need to write a C++ application to load the QML runtime.</p>
<a name="deploying-qml-based-applications"></a>
<h2>Deploying QML-based applications</h2>
<p>To deploy an application that uses QML, the QML runtime must be invoked by the application. This is done by writing a Qt C++ application that loads the <a href="qdeclarativeengine.html">QDeclarativeEngine</a> by either:</p>
<ul>
<li>Loading the QML file through a <a href="qdeclarativeview.html">QDeclarativeView</a> instance, or</li>
<li>Creating a <a href="qdeclarativeengine.html">QDeclarativeEngine</a> instance and loading QML files with <a href="qdeclarativecomponent.html">QDeclarativeComponent</a></li>
</ul>
<a name="deploying-with-qdeclarativeview"></a>
<h3>Deploying with QDeclarativeView</h3>
<p><a href="qdeclarativeview.html">QDeclarativeView</a> is a <a href="qwidget.html">QWidget</a>-based class that is able to load QML files. For example, if there is a QML file, <tt>application.qml</tt>, like this:</p>
<pre class="qml"> import QtQuick 1.0
<span class="type"><a href="qml-rectangle.html">Rectangle</a></span> { <span class="name">width</span>: <span class="number">100</span>; <span class="name">height</span>: <span class="number">100</span>; <span class="name">color</span>: <span class="string">"red"</span> }</pre>
<p>It can be loaded in a Qt application's <tt>main.cpp</tt> file like this:</p>
<pre class="cpp"> <span class="preprocessor">#include <QApplication></span>
<span class="preprocessor">#include <QDeclarativeView></span>
<span class="type">int</span> main(<span class="type">int</span> argc<span class="operator">,</span> <span class="type">char</span> <span class="operator">*</span>argv<span class="operator">[</span><span class="operator">]</span>)
{
<span class="type"><a href="qapplication.html">QApplication</a></span> app(argc<span class="operator">,</span> argv);
<span class="type"><a href="qdeclarativeview.html">QDeclarativeView</a></span> view;
view<span class="operator">.</span>setSource(<span class="type"><a href="qurl.html">QUrl</a></span><span class="operator">::</span>fromLocalFile(<span class="string">"application.qml"</span>));
view<span class="operator">.</span>show();
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}</pre>
<p>This creates a <a href="qwidget.html">QWidget</a>-based view that displays the contents of <tt>application.qml</tt>.</p>
<p>The application's <tt>.pro</tt> <a href="qmake-project-files.html">project file</a> must specify the <tt>declarative</tt> module for the <tt>QT</tt> variable. For example:</p>
<pre class="cpp"> TEMPLATE <span class="operator">+</span><span class="operator">=</span> app
QT <span class="operator">+</span><span class="operator">=</span> gui declarative
SOURCES <span class="operator">+</span><span class="operator">=</span> main<span class="operator">.</span>cpp</pre>
<a name="creating-a-qdeclarativeengine-directly"></a>
<h3>Creating a QDeclarativeEngine directly</h3>
<p>If <tt>application.qml</tt> does not have any graphical components, or if it is preferred to avoid <a href="qdeclarativeview.html">QDeclarativeView</a> for other reasons, the <a href="qdeclarativeengine.html">QDeclarativeEngine</a> can be constructed directly instead. In this case, <tt>application.qml</tt> is loaded as a <a href="qdeclarativecomponent.html">QDeclarativeComponent</a> instance rather than placed into a view:</p>
<pre class="cpp"> <span class="preprocessor">#include <QApplication></span>
<span class="preprocessor">#include <QDeclarativeEngine></span>
<span class="preprocessor">#include <QDeclarativeContext></span>
<span class="preprocessor">#include <QDeclarativeComponent></span>
<span class="type">int</span> main(<span class="type">int</span> argc<span class="operator">,</span> <span class="type">char</span> <span class="operator">*</span>argv<span class="operator">[</span><span class="operator">]</span>)
{
<span class="type"><a href="qapplication.html">QApplication</a></span> app(argc<span class="operator">,</span> argv);
<span class="type"><a href="qdeclarativeengine.html">QDeclarativeEngine</a></span> engine;
<span class="type"><a href="qdeclarativecontext.html">QDeclarativeContext</a></span> <span class="operator">*</span>objectContext <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qdeclarativecontext.html">QDeclarativeContext</a></span>(engine<span class="operator">.</span>rootContext());
<span class="type"><a href="qdeclarativecomponent.html">QDeclarativeComponent</a></span> component(<span class="operator">&</span>engine<span class="operator">,</span> <span class="string">"application.qml"</span>);
<span class="type"><a href="qobject.html">QObject</a></span> <span class="operator">*</span>object <span class="operator">=</span> component<span class="operator">.</span>create(objectContext);
<span class="comment">// ... delete object and objectContext when necessary</span>
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}</pre>
<p>See <a href="qtbinding.html">Using QML Bindings in C++ Applications</a> for more information about using <a href="qdeclarativeengine.html">QDeclarativeEngine</a>, <a href="qdeclarativecontext.html">QDeclarativeContext</a> and <a href="qdeclarativecomponent.html">QDeclarativeComponent</a>, as well as details on including QML files through <a href="resources.html">Qt's Resource system</a>.</p>
<a name="developing-and-prototyping-with-qml-viewer"></a>
<h2>Developing and prototyping with QML Viewer</h2>
<p>The Declarative UI package includes a QML runtime tool, the <i>Qt QML Viewer</i>, which loads and displays QML documents. This is useful during the application development phase for prototyping QML-based applications without writing your own C++ applications to invoke the QML runtime.</p>
<p>See the <a href="qmlviewer.html">QML Viewer</a> documentation for more details.</p>
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