c++ - 如何从状态对象本身而不是外部改变状态？

Question

    class ListenState : public QState
    {
    public:
        ListenState();
        ~ListenState();

    signals:
        void nextState();

    public slots:
        void getSettings();
    };

cpp文件是

ListenState::ListenState()
{
    qDebug() << "Entering ListenState";
}

ListenState::~ListenState()
{
    qDebug() << "Leaving ListenState";
}

void ListenState::getSettings()
{
    Commands cmd;

    cmd.getSettings();

    emit exited( QEvent::None ); // i want to change state now
}

我想做的是当调用 getSettings() 时，我想将状态更改为下一个。我以为我会 emit exited() 但它没有构建。我尝试创建自己的信号 nextState() 但如果我在此函数中发出信号，它也不会编译。

上面的代码错误是:

ListenState.cpp:23: error: C2664: 'QAbstractState::exited' : cannot convert parameter 1 from 'QEvent::Type' to 'QAbstractState::QPrivateSignal' No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

如果我用 emit nextState(); 发出我自己的信号，错误是:

ListenState.obj:-1: error: LNK2001: unresolved external symbol "public: void __thiscall ListenState::nextState(void)" (?nextState@ListenState@@QAEXXZ)

当我处于原始状态时，有没有办法触发从一种状态到另一种状态的转换？

Answer 1

首先，状态的生命周期与何时进入或退出状态关系不大。只要状态机存在，状态通常就存在，或者它们可以即时创建和销毁。您正在连接状态的构造函数和析构函数，并期望在进入或退出状态时调用它们。事实并非如此。

要检查何时进入或退出某个状态，您可以使用以下命令:

void exposeStateTransitions(QState * state, QString name) {
  if (name.isEmpty()) name = state->objectName();
  QObject::connect(state, &QState::entered, []{
    qDebug() << "state" << name << "was entered";
  });
  QObject::connect(state, &QState::exited, []{
    qDebug() << "state" << name << "was exited";
  });
}

其次，状态只能通过使用转换对象来改变。您需要为所需的转换创建一个转换对象，并提供一个信号或事件来触发它:

class ListenState : public QState {
  Q_OBJECT
  QSignalTransition m_transition;
  Q_SIGNAL void settingsTransition();
public:
  ListenState(QState * settingsTarget, QState * parent = 0) : 
    QState(parent), m_transition(this, SIGNAL(settingsTransition())
  {
    m_transition.setTargetState(settingsTarget);
    addTransition(&m_transition);
  }
  void getSettings() {
    ...
    emit settingsTransition();
  }
};

如果您愿意，您也可以即时触发转换:

class ListenState : public QState {
  Q_OBJECT
  QSignalTransition m_transition;
  Q_SIGNAL void settingsTransition();
public:
  ListenState(QState * parent = 0) : 
    QState(parent), m_transition(this, SIGNAL(settingsTransition())
  {
    addTransition(&m_transition);
  }
  void getSettings(QState * target) {
    ...
    m_transition.setTargetState(target);
    emit settingsTransition();
  }
};

您可以使用事件代替信号:

class ListenState : public QState {
  QEventTransition m_transition;
public:
  ListenState(QState * parent = 0) : 
    QState(parent), m_transition(this, QEvent::Leave) {
    addTransition(&m_transition);
  }
  void getSettings(QState * target) {
    ...
    m_transition->setTargetState(target);
    QCoreApplication::postEvent(this, new QEvent(QEvent::Leave));
  }
};