QStateMachine start synchronization

pinchoonet

Hello,

I am working with Qt 4.7, QtCreator 2.2.1 and MS Visual C++ 2003.

I had a bug in my application that I resolved but I would like your opinion about my bug fix.
I wanted to emit a transition signal just after the State Machine has started like this:
@
machine->start();
emit nextState();
@

but this emit was lost and the State Machine stayed in its initial state instead of going to the next state.

I have read the following Qt documentation related to QStateMachine:

"The State Machine Framework":http://developer.qt.nokia.com/doc/qt-4.7/statemachine-api.html
"QStateMachine class":http://developer.qt.nokia.com/doc/qt-4.7/qstatemachine.html
This doc notably says:
slot QStateMachine::start() : "Note: A state machine will not run without a running event loop, such as the main application event loop started with QCoreApplication::exec() or QApplication::exec()."
signal QStateMachine::started() : "This signal is emitted when the state machine has entered its initial state."

Furthermore QStateMachine::start() source code is:
@QMetaObject::invokeMethod(this, "_q_start", Qt::QueuedConnection);@

So I tried to synchronize using QStateMachine::started() signal but when I connect to this signal, QStateMachine::isRunning() boolean says false!
So I used the QState::entered() signal of my machine first state and it worked.

Is it the good way to fix my bug?

I have created a sample application (based on the TwoWayButton Qt sample) to reproduce my bug and fix it.
Here is the code of my sample:

@#include <QtGui>

class QMysteryMachineLabel : public QLabel
{
Q_OBJECT
public:
QMysteryMachineLabel():machine(NULL) {}

signals:
void nextState();

public slots:
void refresh()
{
if (machine == NULL)
{
// States:
// - State OFF
QState *off = new QState();
off->assignProperty(this, "text", "Off");
off->setObjectName("off");
// - State ON
QState *on = new QState();
on->setObjectName("on");
on->assignProperty(this, "text", "On");

        // Transitions
        off->addTransition(this, SIGNAL(nextState()), on);
        on->addTransition(this, SIGNAL(nextState()), off);

        // Machine
        machine = new QStateMachine;
        machine->addState(off);
        machine->addState(on);
        machine->setInitialState(off);
        //
        // This connect does not fix the bug!
        //connect(machine, SIGNAL(started()), this, SLOT(refresh()));
        //
        // This connect is the bug fix
        connect(off, SIGNAL(entered()), this, SLOT(refresh()));
        //
        machine->start(); // State should be Off
    }

    // When refresh() is called for the first time
    // and if I don't use connect before starting the machine,
    // this emit is lost and the state is still Off instead of On
    emit nextState();
}

protected:
QStateMachine *machine;
};

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget w;

QMysteryMachineLabel labelFSM;
QPushButton pushButton("Start FSM");

// Layout
QHBoxLayout hbox;
hbox.addWidget(&labelFSM);
hbox.addWidget(&pushButton);
w.setLayout(&hbox);

QObject::connect(&pushButton, SIGNAL(clicked()), &labelFSM, SLOT(refresh()));

w.show();

return a.exec&#40;&#41;;

}

#include "main.moc"
@

Thanks in advance
Best regards
Pascal