事件过渡范例

class Window : public QWidget
{
public:
    Window(QWidget *parent = 0)
        : QWidget(parent)
    {
        QPushButton *button = new QPushButton(this);
        button->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
        QVBoxLayout *layout = new QVBoxLayout;
        layout->addWidget(button);
        layout->setContentsMargins(80, 80, 80, 80);
        setLayout(layout);

Window class's constructors begins by creating a button.

        QStateMachine *machine = new QStateMachine(this);
        QState *s1 = new QState();
        s1->assignProperty(button, "text", "Outside");
        QState *s2 = new QState();
        s2->assignProperty(button, "text", "Inside");

Two states, s1 and s2 , are created; upon entry they will assign "Outside" and "Inside" to the button's text, respectively.

        QEventTransition *enterTransition = new QEventTransition(button, QEvent::Enter);
        enterTransition->setTargetState(s2);
        s1->addTransition(enterTransition);

When the button receives an event of type QEvent::Enter and the state machine is in state s1 , the machine will transition to state s2 .

        QEventTransition *leaveTransition = new QEventTransition(button, QEvent::Leave);
        leaveTransition->setTargetState(s1);
        s2->addTransition(leaveTransition);

When the button receives an event of type QEvent::Leave and the state machine is in state s2 , the machine will transition back to state s1 .

        QState *s3 = new QState();
        s3->assignProperty(button, "text", "Pressing...");
        QEventTransition *pressTransition = new QEventTransition(button, QEvent::MouseButtonPress);
        pressTransition->setTargetState(s3);
        s2->addTransition(pressTransition);
        QEventTransition *releaseTransition = new QEventTransition(button, QEvent::MouseButtonRelease);
        releaseTransition->setTargetState(s2);
        s3->addTransition(releaseTransition);

Next, the state s3 is created. s3 will be entered when the button receives an event of type QEvent::MouseButtonPress and the state machine is in state s2 . When the button receives an event of type QEvent::MouseButtonRelease and the state machine is in state s3 , the machine will transition back to state s2 .

        machine->addState(s1);
        machine->addState(s2);
        machine->addState(s3);
        machine->setInitialState(s1);
        machine->start();
    }
};

Finally, the states are added to the machine as top-level states, the initial state is set to be s1 ("Outside"), and the machine is started.

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    Window window;
    window.resize(300, 300);
    window.show();
    return app.exec();
}

The main() function constructs a Window object and shows it.

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