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<h1 class="title">Ping Pong States Example</h1>
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<p>Files:</p>
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<li><a href="statemachine-pingpong-main-cpp.html">statemachine/pingpong/main.cpp</a></li>
<li><a href="statemachine-pingpong-pingpong-pro.html">statemachine/pingpong/pingpong.pro</a></li>
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<p>The Ping Pong States example shows how to use parallel states together with custom events and transitions in <a href="statemachine-api.html">The State Machine Framework</a>.<p>This example implements a statechart where two states communicate by posting events to the state machine. The state chart looks as follows:</p>
<p class="centerAlign"><img src="images/pingpong-example.png" alt="" /></p><p>The <tt>pinger</tt> and <tt>ponger</tt> states are parallel states, i.e. they are entered simultaneously and will take transitions independently of eachother.</p>
<p>The <tt>pinger</tt> state will post the first <tt>ping</tt> event upon entry; the <tt>ponger</tt> state will respond by posting a <tt>pong</tt> event; this will cause the <tt>pinger</tt> state to post a new <tt>ping</tt> event; and so on.</p>
<pre class="cpp"> <span class="keyword">class</span> PingEvent : <span class="keyword">public</span> <span class="type"><a href="qevent.html">QEvent</a></span>
{
<span class="keyword">public</span>:
PingEvent() : <span class="type"><a href="qevent.html">QEvent</a></span>(<span class="type"><a href="qevent.html">QEvent</a></span><span class="operator">::</span>Type(<span class="type"><a href="qevent.html">QEvent</a></span><span class="operator">::</span>User<span class="operator">+</span><span class="number">2</span>))
{}
};
<span class="keyword">class</span> PongEvent : <span class="keyword">public</span> <span class="type"><a href="qevent.html">QEvent</a></span>
{
<span class="keyword">public</span>:
PongEvent() : <span class="type"><a href="qevent.html">QEvent</a></span>(<span class="type"><a href="qevent.html">QEvent</a></span><span class="operator">::</span>Type(<span class="type"><a href="qevent.html">QEvent</a></span><span class="operator">::</span>User<span class="operator">+</span><span class="number">3</span>))
{}
};</pre>
<p>Two custom events are defined, <tt>PingEvent</tt> and <tt>PongEvent</tt>.</p>
<pre class="cpp"> <span class="keyword">class</span> Pinger : <span class="keyword">public</span> <span class="type"><a href="qstate.html">QState</a></span>
{
<span class="keyword">public</span>:
Pinger(<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>parent)
: <span class="type"><a href="qstate.html">QState</a></span>(parent) {}
<span class="keyword">protected</span>:
<span class="keyword">virtual</span> <span class="type">void</span> onEntry(<span class="type"><a href="qevent.html">QEvent</a></span> <span class="operator">*</span>)
{
machine()<span class="operator">-</span><span class="operator">></span>postEvent(<span class="keyword">new</span> PingEvent());
fprintf(stdout<span class="operator">,</span> <span class="string">"ping?\n"</span>);
}
};</pre>
<p>The <tt>Pinger</tt> class defines a state that posts a <tt>PingEvent</tt> to the state machine when the state is entered.</p>
<pre class="cpp"> <span class="keyword">class</span> PingTransition : <span class="keyword">public</span> <span class="type"><a href="qabstracttransition.html">QAbstractTransition</a></span>
{
<span class="keyword">public</span>:
PingTransition() {}
<span class="keyword">protected</span>:
<span class="keyword">virtual</span> <span class="type">bool</span> eventTest(<span class="type"><a href="qevent.html">QEvent</a></span> <span class="operator">*</span>e) {
<span class="keyword">return</span> (e<span class="operator">-</span><span class="operator">></span>type() <span class="operator">=</span><span class="operator">=</span> <span class="type"><a href="qevent.html">QEvent</a></span><span class="operator">::</span>User<span class="operator">+</span><span class="number">2</span>);
}
<span class="keyword">virtual</span> <span class="type">void</span> onTransition(<span class="type"><a href="qevent.html">QEvent</a></span> <span class="operator">*</span>)
{
machine()<span class="operator">-</span><span class="operator">></span>postDelayedEvent(<span class="keyword">new</span> PongEvent()<span class="operator">,</span> <span class="number">500</span>);
fprintf(stdout<span class="operator">,</span> <span class="string">"pong!\n"</span>);
}
};</pre>
<p>The <tt>PingTransition</tt> class defines a transition that is triggered by events of type <tt>PingEvent</tt>, and that posts a <tt>PongEvent</tt> (with a delay of 500 milliseconds) to the state machine when the transition is triggered.</p>
<pre class="cpp"> <span class="keyword">class</span> PongTransition : <span class="keyword">public</span> <span class="type"><a href="qabstracttransition.html">QAbstractTransition</a></span>
{
<span class="keyword">public</span>:
PongTransition() {}
<span class="keyword">protected</span>:
<span class="keyword">virtual</span> <span class="type">bool</span> eventTest(<span class="type"><a href="qevent.html">QEvent</a></span> <span class="operator">*</span>e) {
<span class="keyword">return</span> (e<span class="operator">-</span><span class="operator">></span>type() <span class="operator">=</span><span class="operator">=</span> <span class="type"><a href="qevent.html">QEvent</a></span><span class="operator">::</span>User<span class="operator">+</span><span class="number">3</span>);
}
<span class="keyword">virtual</span> <span class="type">void</span> onTransition(<span class="type"><a href="qevent.html">QEvent</a></span> <span class="operator">*</span>)
{
machine()<span class="operator">-</span><span class="operator">></span>postDelayedEvent(<span class="keyword">new</span> PingEvent()<span class="operator">,</span> <span class="number">500</span>);
fprintf(stdout<span class="operator">,</span> <span class="string">"ping?\n"</span>);
}
};</pre>
<p>The <tt>PongTransition</tt> class defines a transition that is triggered by events of type <tt>PongEvent</tt>, and that posts a <tt>PingEvent</tt> (with a delay of 500 milliseconds) to the state machine when the transition is triggered.</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="qcoreapplication.html">QCoreApplication</a></span> app(argc<span class="operator">,</span> argv);
<span class="type"><a href="qstatemachine.html">QStateMachine</a></span> machine;
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>group <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qstate.html">QState</a></span>(<span class="type"><a href="qstate.html">QState</a></span><span class="operator">::</span>ParallelStates);
group<span class="operator">-</span><span class="operator">></span>setObjectName(<span class="string">"group"</span>);</pre>
<p>The main() function begins by creating a state machine and a parallel state group.</p>
<pre class="cpp"> Pinger <span class="operator">*</span>pinger <span class="operator">=</span> <span class="keyword">new</span> Pinger(group);
pinger<span class="operator">-</span><span class="operator">></span>setObjectName(<span class="string">"pinger"</span>);
pinger<span class="operator">-</span><span class="operator">></span>addTransition(<span class="keyword">new</span> PongTransition());
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>ponger <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qstate.html">QState</a></span>(group);
ponger<span class="operator">-</span><span class="operator">></span>setObjectName(<span class="string">"ponger"</span>);
ponger<span class="operator">-</span><span class="operator">></span>addTransition(<span class="keyword">new</span> PingTransition());</pre>
<p>Next, the <tt>pinger</tt> and <tt>ponger</tt> states are created, with the parallel state group as their parent state. Note that the transitions are <i>targetless</i>. When such a transition is triggered, the source state won't be exited and re-entered; only the transition's onTransition() function will be called, and the state machine's configuration will remain the same, which is precisely what we want in this case.</p>
<pre class="cpp"> machine<span class="operator">.</span>addState(group);
machine<span class="operator">.</span>setInitialState(group);
machine<span class="operator">.</span>start();
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}</pre>
<p>Finally, the group is added to the state machine, the machine is started, and the application event loop is entered.</p>
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