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<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 Traffic Light Example (Dynamic)</td></tr></table><table class="buildversion"><tr>
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<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="#dynamically-loading-the-state-machine">Dynamically Loading the State Machine</a></li>
<li class="level1"><a href="#connecting-to-states">Connecting to States</a></li>
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<h1 class="title">Qt SCXML Traffic Light Example (Dynamic)</h1>
<span class="subtitle"></span>
<!-- $$$trafficlight-widgets-dynamic-brief -->
<p>A widget-based application that uses a dynamically loaded state machine to implement a traffic light.</p>
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<div class="descr"> <a name="details"></a>
<p class="centerAlign"><img src="images/trafficlight.png" alt="" /></p><p><i>Traffic Light Example (Dynamic)</i> demonstrates how to connect to the active properties of a state in a dynamically loaded state machine.</p>
<p>The UI is created using Qt Widgets.</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="dynamically-loading-the-state-machine"></a>
<h2 id="dynamically-loading-the-state-machine">Dynamically Loading the State Machine</h2>
<p>We link against the Qt SCXML module by adding the following line to the example <i>.pro</i> file:</p>
<pre class="cpp">
QT += widgets scxml
</pre>
<p>We dynamically create the state machine in <i>trafficlight-widgets-dynamic.cpp</i>:</p>
<pre class="cpp">
<span class="preprocessor">#include "../trafficlight-common/trafficlight.h"</span>
<span class="preprocessor">#include <QApplication></span>
<span class="preprocessor">#include <QTextStream></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><span class="operator">*</span>argv)
{
<span class="type">QApplication</span> app(argc<span class="operator">,</span> argv);
<span class="type"><a href="qscxmlstatemachine.html">QScxmlStateMachine</a></span> <span class="operator">*</span>machine <span class="operator">=</span> <span class="type"><a href="qscxmlstatemachine.html">QScxmlStateMachine</a></span><span class="operator">::</span>fromFile(
<span class="type">QStringLiteral</span>(<span class="string">":statemachine.scxml"</span>));
<span class="keyword">if</span> (<span class="operator">!</span>machine<span class="operator">-</span><span class="operator">></span>parseErrors()<span class="operator">.</span>isEmpty()) {
<span class="type">QTextStream</span> errs(stderr<span class="operator">,</span> <span class="type">QIODevice</span><span class="operator">::</span>WriteOnly);
<span class="keyword">const</span> <span class="keyword">auto</span> errors <span class="operator">=</span> machine<span class="operator">-</span><span class="operator">></span>parseErrors();
<span class="keyword">for</span> (<span class="keyword">const</span> <span class="type"><a href="qscxmlerror.html">QScxmlError</a></span> <span class="operator">&</span>error : errors) {
errs <span class="operator"><</span><span class="operator"><</span> error<span class="operator">.</span>toString();
}
<span class="keyword">return</span> <span class="operator">-</span><span class="number">1</span>;
}
</pre>
<p>And then instantiate it:</p>
<pre class="cpp">
TrafficLight widget(machine);
widget<span class="operator">.</span>show();
machine<span class="operator">-</span><span class="operator">></span>setParent(<span class="operator">&</span>widget);
machine<span class="operator">-</span><span class="operator">></span>start();
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}
</pre>
<a name="connecting-to-states"></a>
<h2 id="connecting-to-states">Connecting to States</h2>
<p>In the SCXML file, we specify states for each light: red, yellow, and green. In the <code><onentry></code> element, we specify the event to send when entering the state and the delay in seconds before sending the event. In the <code><transition></code> element, we specify the event that triggers the transition to the state specified by the <code>target</code> attribute:</p>
<pre class="cpp">
<state id="red">
<onentry>
<send event="startGoingGreen" delay="3s"/>
</onentry>
<transition event="startGoingGreen" target="redGoingGreen"/>
</state>
<state id="yellow" initial="greenGoingRed">
<state id="redGoingGreen">
<onentry>
<send event="goGreen" delay="1s"/>
</onentry>
<transition event="goGreen" target="green"/>
</state>
<state id="greenGoingRed">
<onentry>
<send event="goRed" delay="1s"/>
</onentry>
<transition event="goRed" target="red"/>
</state>
</state>
<state id="green">
<onentry>
<send event="startGoingRed" delay="3s"/>
</onentry>
<transition event="startGoingRed" target="greenGoingRed"/>
</state>
</pre>
<p>We connect to the states as follows:</p>
<pre class="cpp">
machine<span class="operator">-</span><span class="operator">></span>connectToState(<span class="type">QStringLiteral</span>(<span class="string">"red"</span>)<span class="operator">,</span>
widget<span class="operator">-</span><span class="operator">></span>redLight()<span class="operator">,</span> <span class="operator">&</span>LightWidget<span class="operator">::</span>switchLight);
machine<span class="operator">-</span><span class="operator">></span>connectToState(<span class="type">QStringLiteral</span>(<span class="string">"redGoingGreen"</span>)<span class="operator">,</span>
widget<span class="operator">-</span><span class="operator">></span>redLight()<span class="operator">,</span> <span class="operator">&</span>LightWidget<span class="operator">::</span>switchLight);
machine<span class="operator">-</span><span class="operator">></span>connectToState(<span class="type">QStringLiteral</span>(<span class="string">"yellow"</span>)<span class="operator">,</span>
widget<span class="operator">-</span><span class="operator">></span>yellowLight()<span class="operator">,</span> <span class="operator">&</span>LightWidget<span class="operator">::</span>switchLight);
machine<span class="operator">-</span><span class="operator">></span>connectToState(<span class="type">QStringLiteral</span>(<span class="string">"blinking"</span>)<span class="operator">,</span>
widget<span class="operator">-</span><span class="operator">></span>yellowLight()<span class="operator">,</span> <span class="operator">&</span>LightWidget<span class="operator">::</span>switchLight);
machine<span class="operator">-</span><span class="operator">></span>connectToState(<span class="type">QStringLiteral</span>(<span class="string">"green"</span>)<span class="operator">,</span>
widget<span class="operator">-</span><span class="operator">></span>greenLight()<span class="operator">,</span> <span class="operator">&</span>LightWidget<span class="operator">::</span>switchLight);
</pre>
<p>Files:</p>
<ul>
<li><a href="qtscxml-trafficlight-widgets-dynamic-trafficlight-widgets-dynamic-cpp.html">trafficlight-widgets-dynamic/trafficlight-widgets-dynamic.cpp</a></li>
<li><a href="qtscxml-trafficlight-widgets-dynamic-trafficlight-widgets-dynamic-pro.html">trafficlight-widgets-dynamic/trafficlight-widgets-dynamic.pro</a></li>
<li><a href="qtscxml-trafficlight-widgets-dynamic-trafficlight-widgets-dynamic-qrc.html">trafficlight-widgets-dynamic/trafficlight-widgets-dynamic.qrc</a></li>
</ul>
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6ed78e842caa17fd5c94d65d685685e0
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