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<h1 class="title">Traffic Light Example</h1>
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<p>Files:</p>
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<li><a href="statemachine-trafficlight-main-cpp.html">statemachine/trafficlight/main.cpp</a></li>
<li><a href="statemachine-trafficlight-trafficlight-pro.html">statemachine/trafficlight/trafficlight.pro</a></li>
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<p>The Traffic Light example shows how to use <a href="statemachine-api.html">The State Machine Framework</a> to implement the control flow of a traffic light.<p class="centerAlign"><img src="images/trafficlight-example.png" alt="" /></p><p>In this example we write a TrafficLightWidget class. The traffic light has three lights: Red, yellow and green. The traffic light transitions from one light to another (red to yellow to green to yellow to red again) at certain intervals.</p>
<pre class="cpp"> <span class="keyword">class</span> LightWidget : <span class="keyword">public</span> <span class="type"><a href="qwidget.html">QWidget</a></span>
{
Q_OBJECT
Q_PROPERTY(<span class="type">bool</span> on READ isOn WRITE setOn)
<span class="keyword">public</span>:
LightWidget(<span class="keyword">const</span> <span class="type"><a href="qcolor.html">QColor</a></span> <span class="operator">&</span>color<span class="operator">,</span> <span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>)
: <span class="type"><a href="qwidget.html">QWidget</a></span>(parent)<span class="operator">,</span> m_color(color)<span class="operator">,</span> m_on(<span class="keyword">false</span>) {}
<span class="type">bool</span> isOn() <span class="keyword">const</span>
{ <span class="keyword">return</span> m_on; }
<span class="type">void</span> setOn(<span class="type">bool</span> on)
{
<span class="keyword">if</span> (on <span class="operator">=</span><span class="operator">=</span> m_on)
<span class="keyword">return</span>;
m_on <span class="operator">=</span> on;
update();
}
<span class="keyword">public</span> <span class="keyword">slots</span>:
<span class="type">void</span> turnOff() { setOn(<span class="keyword">false</span>); }
<span class="type">void</span> turnOn() { setOn(<span class="keyword">true</span>); }
<span class="keyword">protected</span>:
<span class="keyword">virtual</span> <span class="type">void</span> paintEvent(<span class="type"><a href="qpaintevent.html">QPaintEvent</a></span> <span class="operator">*</span>)
{
<span class="keyword">if</span> (<span class="operator">!</span>m_on)
<span class="keyword">return</span>;
<span class="type"><a href="qpainter.html">QPainter</a></span> painter(<span class="keyword">this</span>);
painter<span class="operator">.</span>setRenderHint(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>Antialiasing);
painter<span class="operator">.</span>setBrush(m_color);
painter<span class="operator">.</span>drawEllipse(<span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> width()<span class="operator">,</span> height());
}
<span class="keyword">private</span>:
<span class="type"><a href="qcolor.html">QColor</a></span> m_color;
<span class="type">bool</span> m_on;
};</pre>
<p>The LightWidget class represents a single light of the traffic light. It provides an <tt>on</tt> property and two slots, turnOn() and turnOff(), to turn the light on and off, respectively. The widget paints itself in the color that's passed to the constructor.</p>
<pre class="cpp"> <span class="keyword">class</span> TrafficLightWidget : <span class="keyword">public</span> <span class="type"><a href="qwidget.html">QWidget</a></span>
{
<span class="keyword">public</span>:
TrafficLightWidget(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>)
: <span class="type"><a href="qwidget.html">QWidget</a></span>(parent)
{
<span class="type"><a href="qvboxlayout.html">QVBoxLayout</a></span> <span class="operator">*</span>vbox <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qvboxlayout.html">QVBoxLayout</a></span>(<span class="keyword">this</span>);
<span class="preprocessor">#ifdef Q_WS_MAEMO_5</span>
vbox<span class="operator">-</span><span class="operator">></span>setContentsMargins(<span class="number">320</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">320</span><span class="operator">,</span> <span class="number">0</span>);
<span class="preprocessor">#endif</span>
m_red <span class="operator">=</span> <span class="keyword">new</span> LightWidget(<span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>red);
vbox<span class="operator">-</span><span class="operator">></span>addWidget(m_red);
m_yellow <span class="operator">=</span> <span class="keyword">new</span> LightWidget(<span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>yellow);
vbox<span class="operator">-</span><span class="operator">></span>addWidget(m_yellow);
m_green <span class="operator">=</span> <span class="keyword">new</span> LightWidget(<span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>green);
vbox<span class="operator">-</span><span class="operator">></span>addWidget(m_green);
<span class="type"><a href="qpalette.html">QPalette</a></span> pal <span class="operator">=</span> palette();
pal<span class="operator">.</span>setColor(<span class="type"><a href="qpalette.html">QPalette</a></span><span class="operator">::</span>Background<span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>black);
setPalette(pal);
setAutoFillBackground(<span class="keyword">true</span>);
}
LightWidget <span class="operator">*</span>redLight() <span class="keyword">const</span>
{ <span class="keyword">return</span> m_red; }
LightWidget <span class="operator">*</span>yellowLight() <span class="keyword">const</span>
{ <span class="keyword">return</span> m_yellow; }
LightWidget <span class="operator">*</span>greenLight() <span class="keyword">const</span>
{ <span class="keyword">return</span> m_green; }
<span class="keyword">private</span>:
LightWidget <span class="operator">*</span>m_red;
LightWidget <span class="operator">*</span>m_yellow;
LightWidget <span class="operator">*</span>m_green;
};</pre>
<p>The TrafficLightWidget class represents the visual part of the traffic light; it's a widget that contains three lights arranged vertically, and provides accessor functions for these.</p>
<pre class="cpp"> <span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>createLightState(LightWidget <span class="operator">*</span>light<span class="operator">,</span> <span class="type">int</span> duration<span class="operator">,</span> <span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>)
{
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>lightState <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qstate.html">QState</a></span>(parent);
<span class="type"><a href="qtimer.html">QTimer</a></span> <span class="operator">*</span>timer <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtimer.html">QTimer</a></span>(lightState);
timer<span class="operator">-</span><span class="operator">></span>setInterval(duration);
timer<span class="operator">-</span><span class="operator">></span>setSingleShot(<span class="keyword">true</span>);
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>timing <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qstate.html">QState</a></span>(lightState);
<span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>connect(timing<span class="operator">,</span> SIGNAL(entered())<span class="operator">,</span> light<span class="operator">,</span> SLOT(turnOn()));
<span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>connect(timing<span class="operator">,</span> SIGNAL(entered())<span class="operator">,</span> timer<span class="operator">,</span> SLOT(start()));
<span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>connect(timing<span class="operator">,</span> SIGNAL(exited())<span class="operator">,</span> light<span class="operator">,</span> SLOT(turnOff()));
<span class="type"><a href="qfinalstate.html">QFinalState</a></span> <span class="operator">*</span>done <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qfinalstate.html">QFinalState</a></span>(lightState);
timing<span class="operator">-</span><span class="operator">></span>addTransition(timer<span class="operator">,</span> SIGNAL(timeout())<span class="operator">,</span> done);
lightState<span class="operator">-</span><span class="operator">></span>setInitialState(timing);
<span class="keyword">return</span> lightState;
}</pre>
<p>The createLightState() function creates a state that turns a light on when the state is entered, and off when the state is exited. The state uses a timer, and as we shall see the timeout is used to transition from one LightState to another. Here is the statechart for the light state:</p>
<p class="centerAlign"><img src="images/trafficlight-example1.png" alt="" /></p><pre class="cpp"> <span class="keyword">class</span> TrafficLight : <span class="keyword">public</span> <span class="type"><a href="qwidget.html">QWidget</a></span>
{
<span class="keyword">public</span>:
TrafficLight(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>)
: <span class="type"><a href="qwidget.html">QWidget</a></span>(parent)
{
<span class="type"><a href="qvboxlayout.html">QVBoxLayout</a></span> <span class="operator">*</span>vbox <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qvboxlayout.html">QVBoxLayout</a></span>(<span class="keyword">this</span>);
TrafficLightWidget <span class="operator">*</span>widget <span class="operator">=</span> <span class="keyword">new</span> TrafficLightWidget();
vbox<span class="operator">-</span><span class="operator">></span>addWidget(widget);
vbox<span class="operator">-</span><span class="operator">></span>setMargin(<span class="number">0</span>);
<span class="type"><a href="qstatemachine.html">QStateMachine</a></span> <span class="operator">*</span>machine <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qstatemachine.html">QStateMachine</a></span>(<span class="keyword">this</span>);
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>redGoingYellow <span class="operator">=</span> createLightState(widget<span class="operator">-</span><span class="operator">></span>redLight()<span class="operator">,</span> <span class="number">3000</span>);
redGoingYellow<span class="operator">-</span><span class="operator">></span>setObjectName(<span class="string">"redGoingYellow"</span>);
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>yellowGoingGreen <span class="operator">=</span> createLightState(widget<span class="operator">-</span><span class="operator">></span>yellowLight()<span class="operator">,</span> <span class="number">1000</span>);
yellowGoingGreen<span class="operator">-</span><span class="operator">></span>setObjectName(<span class="string">"yellowGoingGreen"</span>);
redGoingYellow<span class="operator">-</span><span class="operator">></span>addTransition(redGoingYellow<span class="operator">,</span> SIGNAL(finished())<span class="operator">,</span> yellowGoingGreen);
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>greenGoingYellow <span class="operator">=</span> createLightState(widget<span class="operator">-</span><span class="operator">></span>greenLight()<span class="operator">,</span> <span class="number">3000</span>);
greenGoingYellow<span class="operator">-</span><span class="operator">></span>setObjectName(<span class="string">"greenGoingYellow"</span>);
yellowGoingGreen<span class="operator">-</span><span class="operator">></span>addTransition(yellowGoingGreen<span class="operator">,</span> SIGNAL(finished())<span class="operator">,</span> greenGoingYellow);
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>yellowGoingRed <span class="operator">=</span> createLightState(widget<span class="operator">-</span><span class="operator">></span>yellowLight()<span class="operator">,</span> <span class="number">1000</span>);
yellowGoingRed<span class="operator">-</span><span class="operator">></span>setObjectName(<span class="string">"yellowGoingRed"</span>);
greenGoingYellow<span class="operator">-</span><span class="operator">></span>addTransition(greenGoingYellow<span class="operator">,</span> SIGNAL(finished())<span class="operator">,</span> yellowGoingRed);
yellowGoingRed<span class="operator">-</span><span class="operator">></span>addTransition(yellowGoingRed<span class="operator">,</span> SIGNAL(finished())<span class="operator">,</span> redGoingYellow);
machine<span class="operator">-</span><span class="operator">></span>addState(redGoingYellow);
machine<span class="operator">-</span><span class="operator">></span>addState(yellowGoingGreen);
machine<span class="operator">-</span><span class="operator">></span>addState(greenGoingYellow);
machine<span class="operator">-</span><span class="operator">></span>addState(yellowGoingRed);
machine<span class="operator">-</span><span class="operator">></span>setInitialState(redGoingYellow);
machine<span class="operator">-</span><span class="operator">></span>start();
}
};</pre>
<p>The TrafficLight class combines the TrafficLightWidget with a state machine. The state graph has four states: red-to-yellow, yellow-to-green, green-to-yellow and yellow-to-red. The initial state is red-to-yellow; when the state's timer times out, the state machine transitions to yellow-to-green. The same process repeats through the other states. This is what the statechart looks like:</p>
<p class="centerAlign"><img src="images/trafficlight-example2.png" alt="" /></p><pre class="cpp"> <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"><a href="qapplication.html">QApplication</a></span> app(argc<span class="operator">,</span> argv);
TrafficLight widget;
<span class="preprocessor">#if defined(Q_OS_SYMBIAN)</span>
widget<span class="operator">.</span>showMaximized();
<span class="preprocessor">#elif defined(Q_WS_MAEMO_5) || defined(Q_WS_SIMULATOR)</span>
widget<span class="operator">.</span>show();
<span class="preprocessor">#else</span>
widget<span class="operator">.</span>resize(<span class="number">110</span><span class="operator">,</span> <span class="number">300</span>);
widget<span class="operator">.</span>show();
<span class="preprocessor">#endif</span>
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}</pre>
<p>The main() function constructs a TrafficLight and shows it.</p>
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