<?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 5.12.6</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 5.12</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"><a href="qtscxml-index.html">Qt 5.12.6 Reference Documentation</a></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>
<!-- $$$mediaplayer-qml-cppdatamodel-brief -->
<p>Sends data to and receives it from a C++ data model.</p>
<!-- @@@mediaplayer-qml-cppdatamodel -->
<!-- $$$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="cpp">
<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="cpp">
<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="cpp">
<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-pro.html">mediaplayer-qml-cppdatamodel/mediaplayer-qml-cppdatamodel.pro</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-mediaplayer-qml-cppdatamodel-qrc.html">mediaplayer-qml-cppdatamodel/mediaplayer-qml-cppdatamodel.qrc</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>
</ul>
</div>
<!-- @@@mediaplayer-qml-cppdatamodel -->
</div>
</div>
</div>
</div>
</div>
<div class="footer">
<p>
<acronym title="Copyright">©</acronym> 2019 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>
distrib
>
Mageia
>
7
>
armv7hl
>
media
>
core-updates
>
by-pkgid
>
6ed78e842caa17fd5c94d65d685685e0
>
files
>
123
