Factorial States Example▲
The statechart for calculating the factorial looks as follows:
In other words, the state machine calculates the factorial of 6 and prints the result.
class Factorial : public QObject
{
Q_OBJECT
Q_PROPERTY(int x READ x WRITE setX)
Q_PROPERTY(int fac READ fac WRITE setFac)
public:
using QObject::QObject;
int x() const
{
return m_x;
}
void setX(int x)
{
if (x == m_x)
return;
m_x = x;
emit xChanged(x);
}
int fac() const
{
return m_fac;
}
void setFac(int fac)
{
m_fac = fac;
}
Q_SIGNALS:
void xChanged(int value);
private:
int m_x = -1;
int m_fac = 1;
};The Factorial class is used to hold the data of the computation, x and fac. It also provides a signal that's emitted whenever the value of x changes.
class FactorialLoopTransition : public QSignalTransition
{
public:
FactorialLoopTransition(Factorial *fact)
: QSignalTransition(fact, &Factorial::xChanged), m_fact(fact)
{}
bool eventTest(QEvent *e) override
{
if (!QSignalTransition::eventTest(e))
return false;
QStateMachine::SignalEvent *se = static_cast<QStateMachine::SignalEvent*>(e);
return se->arguments().at(0).toInt() > 1;
}
void onTransition(QEvent *e) override
{
QStateMachine::SignalEvent *se = static_cast<QStateMachine::SignalEvent*>(e);
int x = se->arguments().at(0).toInt();
int fac = m_fact->property("fac").toInt();
m_fact->setProperty("fac", x * fac);
m_fact->setProperty("x", x - 1);
}
private:
Factorial *m_fact;
};The FactorialLoopTransition class implements the guard (x > 1) and calculations (fac = x * fac; x = x - 1) of the factorial loop.
class FactorialDoneTransition : public QSignalTransition
{
public:
FactorialDoneTransition(Factorial *fact)
: QSignalTransition(fact, &Factorial::xChanged), m_fact(fact)
{}
bool eventTest(QEvent *e) override
{
if (!QSignalTransition::eventTest(e))
return false;
QStateMachine::SignalEvent *se = static_cast<QStateMachine::SignalEvent*>(e);
return se->arguments().at(0).toInt() <= 1;
}
void onTransition(QEvent *) override
{
qInfo() << m_fact->property("fac").toInt();
}
private:
Factorial *m_fact;
};The FactorialDoneTransition class implements the guard (x <= 1) that terminates the factorial computation. It also prints the final result to standard output.
int main(int argc, char **argv)
{
QCoreApplication app(argc, argv);
Factorial factorial;
QStateMachine machine;The application's main() function first creates the application object, a Factorial object and a state machine.
QState *compute = new QState(&machine);
compute->assignProperty(&factorial, "fac", 1);
compute->assignProperty(&factorial, "x", 6);
compute->addTransition(new FactorialLoopTransition(&factorial));The compute state is created, and the initial values of x and fac are defined. A FactorialLoopTransition object is created and added to the state.
QFinalState *done = new QFinalState(&machine);
FactorialDoneTransition *doneTransition = new FactorialDoneTransition(&factorial);
doneTransition->setTargetState(done);
compute->addTransition(doneTransition);A final state, done, is created, and a FactorialDoneTransition object is created with done as its target state. The transition is then added to the compute state.
machine.setInitialState(compute);
QObject::connect(&machine, &QStateMachine::finished, &app, QCoreApplication::quit);
machine.start();
return app.exec();
}The machine's initial state is set to be the compute state. We connect the QStateMachine::finished() signal to the QCoreApplication::quit() slot, so the application will quit when the state machine's work is done. Finally, the state machine is started, and the application's event loop is entered.