<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html> <html lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <!-- mediaplayer-qml-cppdatamodel.qdoc --> <title>Qt SCXML Media Player QML Example (C++ Data Model) | Qt SCXML 5.9</title> <link rel="stylesheet" type="text/css" href="style/offline-simple.css" /> <script type="text/javascript"> document.getElementsByTagName("link").item(0).setAttribute("href", "style/offline.css"); // loading style sheet breaks anchors that were jumped to before // so force jumping to anchor again setTimeout(function() { var anchor = location.hash; // need to jump to different anchor first (e.g. none) location.hash = "#"; setTimeout(function() { location.hash = anchor; }, 0); }, 0); </script> </head> <body> <div class="header" id="qtdocheader"> <div class="main"> <div class="main-rounded"> <div class="navigationbar"> <table><tr> <td >Qt 5.9</td><td ><a href="qtscxml-index.html">Qt SCXML</a></td><td ><a href="examples-qtscxml.html">Qt SCXML Examples</a></td><td >Qt SCXML Media Player QML Example (C++ Data Model)</td></tr></table><table class="buildversion"><tr> <td id="buildversion" width="100%" align="right">Qt 5.9.4 Reference Documentation</td> </tr></table> </div> </div> <div class="content"> <div class="line"> <div class="content mainContent"> <div class="sidebar"> <div class="toc"> <h3><a name="toc">Contents</a></h3> <ul> <li class="level1"><a href="#running-the-example">Running the Example</a></li> <li class="level1"><a href="#using-the-c-data-model">Using the C++ Data Model</a></li> </ul> </div> <div class="sidebar-content" id="sidebar-content"></div></div> <h1 class="title">Qt SCXML Media Player QML Example (C++ Data Model)</h1> <span class="subtitle"></span> <!-- $$$mediaplayer-qml-cppdatamodel-description --> <div class="descr"> <a name="details"></a> <p class="centerAlign"><img src="images/mediaplayer.png" alt="" /></p><p><i>Media Player QML Example (C++ Data Model)</i> demonstrates how to access data from a C++ data model. The data model enables writing C++ code for <i>expr</i> attributes and <code><script></code> elements. The <i>data part</i> of the data model is backed by a subclass of <a href="qscxmlcppdatamodel.html">QScxmlCppDataModel</a>, for which the Qt SCXML compiler (<code>qscxmlc</code>) generates the dispatch methods.</p> <p>The UI is created using Qt Quick.</p> <a name="running-the-example"></a> <h2 id="running-the-example">Running the Example</h2> <p>To run the example from Qt Creator, open the <b>Welcome</b> mode and select the example from <b>Examples</b>. For more information, visit Building and Running an Example.</p> <a name="using-the-c-data-model"></a> <h2 id="using-the-c-data-model">Using the C++ Data Model</h2> <p>We specify the data model as a value of the <i>datamodel</i> attribute of the <code><scxml></code> element in the SCXML file:</p> <pre class="qml"> <scxml xmlns="http://www.w3.org/2005/07/scxml" version="1.0" name="MediaPlayerStateMachine" initial="stopped" datamodel="cplusplus:TheDataModel:thedatamodel.h" </pre> <p>The format of the <i>datamodel</i> attribute is: <code>cplusplus:<class-name>:<classdef-header></code>. Therefore, we need a file called <i>thedatamodel.h</i> that contains a subclass of <a href="qscxmlcppdatamodel.html">QScxmlCppDataModel</a>:</p> <pre class="qml"> <span class="preprocessor">#include "qscxmlcppdatamodel.h"</span> <span class="keyword">class</span> TheDataModel: <span class="keyword">public</span> <span class="type"><a href="qscxmlcppdatamodel.html">QScxmlCppDataModel</a></span> { Q_OBJECT Q_SCXML_DATAMODEL </pre> <p><a href="qscxmlcppdatamodel.html">QScxmlCppDataModel</a> derives from QObject, so we add the <code>Q_OBJECT</code> macro in the private section of the definition, right after the opening bracket. We then place the <code>Q_SCXML_DATAMODEL</code> macro after <code>Q_OBJECT</code>. The macro expands to the declaration of virtual methods, the implementation of which is generated by the Qt SCXML compiler.</p> <p>In the SCXML file, we specify C++ statements in the <code><script></code> element and use the <i>expr</i> attribute to access the data model:</p> <pre class="qml"> <state id="stopped"> <transition event="tap" cond="isValidMedia()" target="playing"/> </state> <state id="playing"> <onentry> <script> media = eventData().value(QStringLiteral(&quot;media&quot;)).toString(); </script> <send event="playbackStarted"> <param name="media" expr="media"/> </send> </onentry> <onexit> <send event="playbackStopped"> <param name="media" expr="media"/> </send> </onexit> <transition event="tap" cond="!isValidMedia() || media == eventData().value(QStringLiteral(&quot;media&quot;))" target="stopped"/> <transition event="tap" cond="isValidMedia() &amp;&amp; media != eventData().value(QStringLiteral(&quot;media&quot;))" target="playing"/> </state> </pre> <p>The Qt SCXML compiler generates the various <code>evaluateTo</code> methods and converts the expressions and scripts into lambdas inside those methods in <i>mediaplayer-cppdatamodel.cpp</i>:</p> <pre class="cpp"> bool TheDataModel<span class="operator">::</span>evaluateToBool(<span class="type"><a href="qscxmlexecutablecontent.html">QScxmlExecutableContent</a></span><span class="operator">::</span>EvaluatorId id<span class="operator">,</span> bool <span class="operator">*</span>ok) { <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span><span class="operator">.</span> <span class="keyword">return</span> <span class="operator">[</span><span class="keyword">this</span><span class="operator">]</span>()<span class="operator">-</span><span class="operator">></span>bool{ <span class="keyword">return</span> isValidMedia(); }(); <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span><span class="operator">.</span> } <span class="type">QVariant</span> TheDataModel<span class="operator">::</span>evaluateToVariant(<span class="type"><a href="qscxmlexecutablecontent.html">QScxmlExecutableContent</a></span><span class="operator">::</span>EvaluatorId id<span class="operator">,</span> bool <span class="operator">*</span>ok) { <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span><span class="operator">.</span> <span class="keyword">return</span> <span class="operator">[</span><span class="keyword">this</span><span class="operator">]</span>()<span class="operator">-</span><span class="operator">></span><span class="type">QVariant</span>{ <span class="keyword">return</span> media; }(); <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span><span class="operator">.</span> } <span class="type">void</span> TheDataModel<span class="operator">::</span>evaluateToVoid(<span class="type"><a href="qscxmlexecutablecontent.html">QScxmlExecutableContent</a></span><span class="operator">::</span>EvaluatorId id<span class="operator">,</span> bool <span class="operator">*</span>ok) { <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span><span class="operator">.</span> <span class="operator">[</span><span class="keyword">this</span><span class="operator">]</span>()<span class="operator">-</span><span class="operator">></span><span class="type">void</span>{ media <span class="operator">=</span> eventData()<span class="operator">.</span>value(<span class="type">QStringLiteral</span>(<span class="string">"media"</span>))<span class="operator">.</span>toString(); }(); <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span><span class="operator">.</span> } </pre> <p>Files:</p> <ul> <li><a href="qtscxml-mediaplayer-qml-cppdatamodel-mediaplayer-cppdatamodel-cpp.html">mediaplayer-qml-cppdatamodel/mediaplayer-cppdatamodel.cpp</a></li> <li><a href="qtscxml-mediaplayer-qml-cppdatamodel-mediaplayer-cppdatamodel-h.html">mediaplayer-qml-cppdatamodel/mediaplayer-cppdatamodel.h</a></li> <li><a href="qtscxml-mediaplayer-qml-cppdatamodel-mediaplayer-cppdatamodel-scxml.html">mediaplayer-qml-cppdatamodel/mediaplayer-cppdatamodel.scxml</a></li> <li><a href="qtscxml-mediaplayer-qml-cppdatamodel-mediaplayer-qml-cppdatamodel-cpp.html">mediaplayer-qml-cppdatamodel/mediaplayer-qml-cppdatamodel.cpp</a></li> <li><a href="qtscxml-mediaplayer-qml-cppdatamodel-mediaplayer-qml-cppdatamodel-qml.html">mediaplayer-qml-cppdatamodel/mediaplayer-qml-cppdatamodel.qml</a></li> <li><a href="qtscxml-mediaplayer-qml-cppdatamodel-thedatamodel-cpp.html">mediaplayer-qml-cppdatamodel/thedatamodel.cpp</a></li> <li><a href="qtscxml-mediaplayer-qml-cppdatamodel-thedatamodel-h.html">mediaplayer-qml-cppdatamodel/thedatamodel.h</a></li> <li><a href="qtscxml-mediaplayer-qml-cppdatamodel-mediaplayer-qml-cppdatamodel-pro.html">mediaplayer-qml-cppdatamodel/mediaplayer-qml-cppdatamodel.pro</a></li> <li><a href="qtscxml-mediaplayer-qml-cppdatamodel-mediaplayer-qml-cppdatamodel-qrc.html">mediaplayer-qml-cppdatamodel/mediaplayer-qml-cppdatamodel.qrc</a></li> </ul> </div> <!-- @@@mediaplayer-qml-cppdatamodel --> </div> </div> </div> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2017 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners.<br> The documentation provided herein is licensed under the terms of the <a href="http://www.gnu.org/licenses/fdl.html">GNU Free Documentation License version 1.3</a> as published by the Free Software Foundation.<br> Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners. </p> </div> </body> </html>