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:
Factorial(QObject *parent = 0)
: QObject(parent), m_x(-1), m_fac(1)
{
}
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;
int m_fac;
};
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, SIGNAL(xChanged(int))), 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, SIGNAL(xChanged(int))), 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 { fprintf(stdout, "%d\n", 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, SIGNAL(finished()), &app, SLOT(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.
Files: