transitions.cpp Example File

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    #include "transitions.hpp"
    #include "factorial.hpp"

    #include <QtCore/QStateMachine>

    /**
     * This transition inherits from QSignalTransition and passes 'fact' and 'SIGNAL(xChanged(int))'
     * to the constructor of the base class. That means whenever 'fact' emits the 'xChanged(int)' signal,
     * the state machine will try to invoke this transition.
     */
    FactorialLoopTransition::FactorialLoopTransition(Factorial *fact)
        : QSignalTransition(fact, SIGNAL(xChanged(int)))
        , m_fact(fact)
    {
    }

    bool FactorialLoopTransition::eventTest(QEvent *e)
    {
        // Check if the base class accepts this transition
        if (!QSignalTransition::eventTest(e))
            return false;

        /**
         * We have to evaluate the parameter that is passed with the 'xChanged(int)' signal,
         * so we cast the passed QEvent object to the special QStateMachine::SignalEvent.
         * The signal events provides access to the passed parameters via its arguments() method.
         */
        QStateMachine::SignalEvent *se = static_cast<QStateMachine::SignalEvent*>(e);

        // Allow the transition (that means return 'true') as long as x > 1
        return se->arguments().at(0).toInt() > 1;
    }

    void FactorialLoopTransition::onTransition(QEvent *e)
    {
        // This method is called when the transition is executed

        // Retrieve the 'x' value from the signal event and the 'fac' value from the Factorial object
        QStateMachine::SignalEvent *se = static_cast<QStateMachine::SignalEvent*>(e);
        const int x = se->arguments().at(0).toInt();
        const int fac = m_fact->property("fac").toInt();

        // Update the 'fac' property of the Factorial object
        m_fact->setProperty("fac", x * fac);

        /**
         * Decrement the 'x' property of the Factorial object.
         *
         * Note: This will cause the Factorial object to emit the 'xChanged(int)' signal and
         *       that will trigger the state machine to invoke this transition again -> it loops.
         */
        m_fact->setProperty("x", x - 1);
    }

    /**
     * This transition inherits from QSignalTransition and passes 'fact' and 'SIGNAL(xChanged(int))'
     * to the constructor of the base class. That means whenever 'fact' emits the 'xChanged(int)' signal,
     * the state machine will try to invoke this transition.
     */
    FactorialDoneTransition::FactorialDoneTransition(Factorial *fact)
        : QSignalTransition(fact, SIGNAL(xChanged(int)))
        , m_fact(fact)
    {
    }

    bool FactorialDoneTransition::eventTest(QEvent *e)
    {
        // Check if the base class accepts this transition
        if (!QSignalTransition::eventTest(e))
            return false;

        QStateMachine::SignalEvent *se = static_cast<QStateMachine::SignalEvent*>(e);

        // Allow the transition (that means return 'true') only if x <= 1
        return se->arguments().at(0).toInt() <= 1;
    }