int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    QPushButton button;
    QStateMachine machine;

The application's main() function begins by constructing the application object, a button and a state machine.

    QState *off = new QState();
    off->assignProperty(&button, "text", "Off");
    off->setObjectName("off");

    QState *on = new QState();
    on->setObjectName("on");
    on->assignProperty(&button, "text", "On");

The state machine has two states; on and off. When either state is entered, the text of the button will be set accordingly.

    off->addTransition(&button, SIGNAL(clicked()), on);
    on->addTransition(&button, SIGNAL(clicked()), off);

When the state machine is in the off state and the button is clicked, it will transition to the on state; when the state machine is in the on state and the button is clicked, it will transition to the off state.

    machine.addState(off);
    machine.addState(on);

The states are added to the state machine; they become top-level (sibling) states.

    machine.setInitialState(off);
    machine.start();

The initial state is off; this is the state the state machine will immediately transition to once the state machine is started.

    button.resize(100, 50);
    button.show();
    return app.exec();
}

Finally, the button is resized and made visible, and the application event loop is entered.

Files:

• statemachine/twowaybutton/main.cpp
• statemachine/twowaybutton/twowaybutton.pro