如果QStateMachine中的转换成功，则从类发出信号

Question

我的问题是:我需要创建包含QStateMachine实例的类。这个类应该有槽，您可以通过这些槽“请求”状态机向另一个状态进行转换。如果过渡成功，我们班应该发出信号。我将如何实现这一点？类应该具有根据特定时隙调用发出特定信号的能力。下面是一个小的类示例：

class MyClass : public QObject
{
    Q_OBJECT
public:
    explicit MyClass(QObject *parent = 0)
    {
        mStateMachine = new QStateMachine(this);
        QState *s1 = new QState(mStateMachine);
        QState *s2 = new QState(mStateMachine);
        QState *s3 = new QState(mStateMachine);

        s1->addTransition(); // Transition to s2
        s2->addTransition(); // Transition to s3
        s3->addTransition(); // Transition to s1

        mStateMachine->setInitialState(s1);
        mStateMachine->start();
    }

signals:
    toS1();
    toS2();
    toS3();

public slots:
    slotToS1()
    {
        /* post event to state machine about
        transition to state s1,
        if transition was successful,
        then emit toS1() signal. */
    };
    slotToS2(){ /* Similar to slotToS1 */};
    slotToS3(){ /* Similar to slotToS1 */};
private:
    QStateMachine *mStateMachine;
}

我将非常感谢您的帮助！

UPD：

插槽表示不同类型的转换，因此外部类(将使用MyClass)可以“请求”某些转换。因此，时隙将事件或信号发送到状态机，它会查看事件或信号，并且(如果处于正确的状态)进行此转换。我想用一定的信号通知外级，这是在插槽(转换)成功之前询问的。

Answer 1

1. 要在时隙调用上进行转换，需要以某种方式将时隙绑定到QAbstractTransition。有两种方法可以做到：

- Use a `QEventTransition` and send a relevant event to trigger it.
- Use a `QSignalTransition` and use an internal signal to trigger it.

​

1. 若要在状态转换时发出信号，可以将QAbstractTransition::triggered或QState::entered或QState::exited信号连接到其他信号。记住，在Qt中，连接目标可以是插槽，也可以是信号。

因此，使用信号转换：

class MyClass : public QObject
{
  Q_OBJECT
  QStateMachine machine;
  QState s1, s2;
  Q_SIGNAL void s_go_s1_s2();
  Q_SIGNAL void s_go_s2_s1();
public:
  Q_SIGNAL void transitioned_s1_s2();
  Q_SIGNAL void transitioned_s2_s1();
  Q_SLOT void go_s2_s1() { emit s_go_s2_s1(); }
  Q_SLOT void go_s1_s2() { emit s_go_s1_s2(); }
  explicit MyClass(QObject *parent = 0) : QObject(parent),
    s1(&machine), s2(&machine) {
    auto s1_s2 = s1.addTransition(this, SIGNAL(s_go_s1_s2()), &s2);
    auto s2_s1 = s2.addTransition(this, SIGNAL(s_go_s2_s1()), &s1);
    machine.setInitialState(&s1);
    machine.start();
    connect(s1_s2, &QAbstractTransition::triggered, this, &MyClass:: transitioned_s1_s2);
    connect(s2_s1, &QAbstractTransition::triggered, this, &MyClass:: transitioned_s2_s1);
  }
}

使用事件转换有点困难，因为使用的事件必须是状态机可以复制的。核心模块的状态机只知道如何克隆None和Timer事件--参见其cloneEvent实现。

Widget模块添加了对各种GUI/Widget事件的支持--请参见那里的cloneEvent实现。在必要的情况下，您可以将此类GUI事件用于您自己的目的--毕竟，它们被发送到一个普通的QObject中，它不会以特殊的方式对它们进行解释。

您可以提供自己的cloneEvent实现，与其他实现链接。

#include <private/qstatemachine_p.h>

class MyClass : public QObject
{
  Q_OBJECT
  QStateMachine machine;
  QState s1, s2;
  QEvent e_s1_s2, e_s2_s1;
  QEventTransition s1_s2, s2_s1;
public:
  Q_SIGNAL void transitioned_s1_s2();
  Q_SIGNAL void transitioned_s2_s1();
  Q_SLOT void go_s2_s1() { QCoreApplication::sendEvent(this, &e_s2_s1); }
  Q_SLOT void go_s1_s2() { QCoreApplication::sendEvent(this, &e_s1_s2); }
  explicit MyClass(QObject *parent = 0) : QObject(parent),
    s1(&machine), s2(&machine),
    e_s1_s2((QEvent::Type)(QEvent::User + 1)),
    e_s2_s1((QEvent::Type)(QEvent::User + 2)),
    s1_s2(this, e_s1_s2.type()),
    s2_s1(this, e_s2_s1.type()) {
    s1_s2.setTargetState(&s2);
    s2_s1.setTargetState(&s1);
    s1.addTransition(&s1_s2);
    s2.addTransition(&s2_s1);
    machine.setInitialState(&s1);
    machine.start();
    connect(&s1_s2, &QAbstractTransition::triggered, this, &MyClass::transitioned_s1_s2);
    connect(&s2_s1, &QAbstractTransition::triggered, this, &MyClass::transitioned_s2_s1);
  }
}

static const QStateMachinePrivate::Handler * last_handler = 0;

static QEvent * cloneEvent(QEvent * e) {
  if (e->type() >= QEvent::User && e->type() < QEvent::User+100) {
    return new QEvent(e->type());
  return last_handler->cloneEvent(e);
}

const QStateMachinePrivate::Handler our_handler = {
    cloneEvent
};

void registerHandler() {
  last_handler = QStateMachinePrivate::handler;
  QStateMachinePrivate::handler = &our_handler;
}
Q_CONSTRUCTOR_FUNCTION(registerHandler())

void unregisterHandler() {
  QStateMachinePrivate::handler = last_handler;

}
Q_DESTRUCTOR_FUNCTION(unregisterHandler())

Answer 2

我过去也遇到过同样的问题，我发现最简单的方法是使用您自己的QState类继承QState，并实现两个方法，名为QState::onEntry(QEvent * event)和QState::onExit(QEvent * event)。

这样，您就可以在退出和进入新状态时发出任何您喜欢的信号。

下面是一个例子：

文件mystate.h

#include <QState>

class MyState : public QState
{
    Q_OBJECT
public:
    explicit MyState(qint32 stateId, QState * parent = 0);

protected:
    void onEntry(QEvent * event);
    void onExit(QEvent * event);
 
signals:
    void exit(qint32 stateId);
    void enter(qint32 stateId);
  
private: 
    qint32 stateId;  
};

和文件mystate.cpp

#include "mystate.h"


MyState::MyState(qint32 stateId, QState *parent)
{
    this->stateId = stateId;
}

void MyState::onEntry(QEvent *event)
{
    emit enter(stateId);
}

void MyState::onExit(QEvent *event)
{
    emit (exit(stateId));
}