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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 QML Example (Simple)</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="#compiling-the-state-machine">Compiling the State Machine</a></li>
<li class="level1"><a href="#instantiating-the-state-machine">Instantiating 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 QML Example (Simple)</h1>
<span class="subtitle"></span>
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<p>A Qt Quick application that uses a compiled state machine to implement a simplified 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 QML Example (Simple)</i> demonstrates how to connect to the active properties of a state in a state machine that is compiled to a class.</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="compiling-the-state-machine"></a>
<h2 id="compiling-the-state-machine">Compiling the State Machine</h2>
<p>We link against the Qt SCXML module by adding the following line to the <i>.pro</i> file:</p>
<pre class="cpp">
QT += qml scxml
</pre>
<p>We then specify the state machine to compile:</p>
<pre class="cpp">
STATECHARTS = ../trafficlight-common/statemachine.scxml
</pre>
<p>The Qt SCXML Compiler, <code>qscxmlc</code>, is run automatically to generate <i>statemachine.h</i> and <i>statemachine.cpp</i>, and to add them to the <code>HEADERS</code> and <code>SOURCES</code> variables for compilation.</p>
<a name="instantiating-the-state-machine"></a>
<h2 id="instantiating-the-state-machine">Instantiating the State Machine</h2>
<p>We instantiate the state machine as follows:</p>
<pre class="cpp">
TrafficLightStateMachine {
id: stateMachine
running: true
}
</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">
Light {
anchors.top: parent.top
anchors.horizontalCenter: parent.horizontalCenter
color: "red"
visible: stateMachine.red || stateMachine.redGoingGreen
}
Light {
anchors.centerIn: parent
color: "yellow"
visible: stateMachine.yellow || stateMachine.blinking
}
Light {
anchors.bottom: parent.bottom
anchors.horizontalCenter: parent.horizontalCenter
color: "green"
visible: stateMachine.green
}
}
</pre>
<p>Files:</p>
<ul>
<li><a href="qtscxml-trafficlight-qml-simple-light-qml.html">trafficlight-qml-simple/Light.qml</a></li>
<li><a href="qtscxml-trafficlight-qml-simple-trafficlight-qml.html">trafficlight-qml-simple/TrafficLight.qml</a></li>
<li><a href="qtscxml-trafficlight-qml-simple-statemachine-cpp.html">trafficlight-qml-simple/statemachine.cpp</a></li>
<li><a href="qtscxml-trafficlight-qml-simple-statemachine-h.html">trafficlight-qml-simple/statemachine.h</a></li>
<li><a href="qtscxml-trafficlight-qml-simple-trafficlight-qml-simple-cpp.html">trafficlight-qml-simple/trafficlight-qml-simple.cpp</a></li>
<li><a href="qtscxml-trafficlight-qml-simple-trafficlight-qml-simple-pro.html">trafficlight-qml-simple/trafficlight-qml-simple.pro</a></li>
<li><a href="qtscxml-trafficlight-qml-simple-trafficlight-qml-simple-qrc.html">trafficlight-qml-simple/trafficlight-qml-simple.qrc</a></li>
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