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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 Calculator QML Example</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>
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<h1 class="title">Qt SCXML Calculator QML Example</h1>
<span class="subtitle"></span>
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<p>A Qt Quick application that implements the Calculator example presented in the SCXML Specification.</p>
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<div class="descr"> <a name="details"></a>
<p class="centerAlign"><img src="images/calculator-qml.png" alt="" /></p><p><i>Calculator</i> uses Qt SCXML to implement the <a href="http://www.w3.org/TR/scxml/#N11630">Calculator Example</a> presented in the SCXML Specification.</p>
<p>The state machine is specified in the <i>statemachine.scxml</i> file and compiled into the <code>CalculatorStateMachine</code> class. The user interface 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 += widgets scxml
</pre>
<p>We then specify the state machine to compile:</p>
<pre class="cpp">
STATECHARTS = ../calculator-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 make the generated <code>CalculatorStateMachine</code> class available to QML by registering it as a QML type in the <i>calculator-qml.cpp</i> file:</p>
<pre class="cpp">
<span class="preprocessor">#include "statemachine.h"</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">QGuiApplication</span> app(argc<span class="operator">,</span> argv);
qmlRegisterType<span class="operator"><</span>CalculatorStateMachine<span class="operator">></span>(<span class="string">"CalculatorStateMachine"</span><span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span>
<span class="string">"CalculatorStateMachine"</span>);
<span class="type">QQmlApplicationEngine</span> engine;
engine<span class="operator">.</span>load(<span class="type">QUrl</span>(<span class="type">QStringLiteral</span>(<span class="string">"qrc:/calculator-qml.qml"</span>)));
<span class="keyword">if</span> (engine<span class="operator">.</span>rootObjects()<span class="operator">.</span>isEmpty())
<span class="keyword">return</span> <span class="operator">-</span><span class="number">1</span>;
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}
</pre>
<p>To use the CalculatorStateMachine type in a QML file, we import it:</p>
<pre class="cpp">
import CalculatorStateMachine 1.0
</pre>
<p>We instantiate a CalculatorStateMachine and listen to the <code>updateDisplay</code> event. When it occurs, we change the text on the calculator display:</p>
<pre class="cpp">
CalculatorStateMachine {
id: statemachine
running: true
EventConnection {
events: ["updateDisplay"]
onOccurred: resultText.text = event.data.display
}
}
</pre>
<p>When users press the calculator buttons, the buttons submit events to the state machine:</p>
<pre class="cpp">
Button {
id: resultButton
x: 3 * width
y: parent.height / 5
textHeight: y - 2
fontHeight: 0.4
width: parent.width / 4
height: y * 4
color: pressed ? "#e0b91c" : "#face20"
text: "="
onClicked: statemachine.submitEvent("EQUALS")
}
</pre>
<p>Files:</p>
<ul>
<li><a href="qtscxml-calculator-qml-button-qml.html">calculator-qml/Button.qml</a></li>
<li><a href="qtscxml-calculator-qml-calculator-qml-cpp.html">calculator-qml/calculator-qml.cpp</a></li>
<li><a href="qtscxml-calculator-qml-calculator-qml-pro.html">calculator-qml/calculator-qml.pro</a></li>
<li><a href="qtscxml-calculator-qml-calculator-qml-qml.html">calculator-qml/calculator-qml.qml</a></li>
<li><a href="qtscxml-calculator-qml-calculator-qml-qrc.html">calculator-qml/calculator-qml.qrc</a></li>
<li><a href="qtscxml-calculator-qml-statemachine-cpp.html">calculator-qml/statemachine.cpp</a></li>
<li><a href="qtscxml-calculator-qml-statemachine-h.html">calculator-qml/statemachine.h</a></li>
</ul>
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