Pass parameters to a QState

[kain]

Hello,

I have a QStateMachine which controls some MotorControl-logic. Basically it is a StateMachine which models the behavior of an cover/door which can be opened or closed.
Therefore I want to have 3 QStates: 'Open', 'Moving' and 'Closed'. The state "Moving" is a QStateMachine itself and models the process of controlling my motor. However, I need to pass parameters to that QStateMachine somehow because it needs to know, wether it should open or close the cover.
What I did up until know is, that I just created 2 "Moving" QStateMachines, one as "Opening" and one as "Closing" and passed the parameters via constructor.
This might be sufficent in simple cases, but I need to be able to pass parameters to that QStateMachine using the signal which triggers the transition into that QStateMachine.
Is there any way to achieve that?

[dheerendra]

You can subclass QState and define the member variables,signals,slots required. You can set /use these values appropriately.

[kain]

Okay, I am not sure how to do that.
My current approach is this:

#ifndef SMAXISPOSITIONING_H
#define SMAXISPOSITIONING_H

#include <QStateMachine>
#include "axiscontrol.h"

class SmAxisPositioning : public QStateMachine
{
    Q_OBJECT
public:
    explicit SmAxisPositioning(AxisControl *control, QStateMachine *parent = nullptr);
    long TargetPosition;
    long MovementSpeed;
    long Acceleration;
private:
    AxisControl *axisControl;
signals:
    void step();
    void retry();
    void error();
    void done();
public slots:
    void onEnable();
    void onWaitEnable();
    void onPosition();
    void onWaitPosition();
};

#endif // SMAXISPOSITIONING_H

I want this QStateMachine to set parameters on the "OnEntry"-Slot. How would I pass data into that slot then? OnEntry is called by the parent StateMachine...

[dheerendra]

QStateMachine should hold the states and transition the states. It is better you define the three states called Open, Move and Close. You should add these states to State Machine and control the transition. In turn each state should carry out its task.

You need define statement like Motor is object. This object is the state called Open, Close, Moving. When motor is appropriate state called - moving, state should automatically carry out the task assigned for that state. Now State machine role is just manage the different state and do the transition.

In your case, you are making the StateMachine itself as "Moving" state. So you are overloading the meaning of stjatemachine. According to me it is not a good idea.

Hope it is clear.

[kain]

I am not sure about what you are suggesting. The reason the "Moving" state itself is a QStateMachine is to reduce the complexity.
My parent statemachine looke like this:

public:
    explicit CoverStateMachine(AxisControl *axisControl, QObject *parent = nullptr);
private:
    AxisControl *axisControl;
    QState* stateOpen;
    SmAxisPositioning* stateClosing;
    SmAxisPositioning* stateOpening;
    QState* stateClosed;
    QState* stateError;
signals:
    void closeCover();
    void openCover();
public slots:
    //Commands
    void cmdCloseCover();
    void cmdOpenCover();
};

#endif // COVERSTATEMACHINE_H

The advantage by modelling my process as statemachine is that it is 'interruptable' by different signals.

[dheerendra]

Moving, Open, Close are different states. It is better to represent them as different QState. It is more readable, maintainable. Now your system has three states. It moves between these states. Each of these state itself should define what action to be carried out for each of those states. Now you need QstateMachine to transition between these states. This is how statemachine need to work. We can put QState inside QStateMachine & it works. However it puts the StateMachine with two responsibilities(StateMachine & State). This code confuses the overall state machine working.

[SGaist]

Hi,

Aren't you complicating things a bit ?
You could have four states:

1. Closed
2. Opening
3. Open
4. Closing

Wouldn't that be simpler to manage your door ?

[kain]

Well, right now I got 4 states which is fine for me.
But I got different cases where I have to be able to position that cover (or any other motor) to a specific position.
For example that CoverStateMachine above would have a Slot

void cmdPositionCover(int position, int speed, int acceleration);

In this case I can not just have 2 states 'Opening' and 'Closing' but need a more general approach where I could pass the slots parameter into the QState/QStateMachine which handles the movement of that cover. I can't have an infinite number of QStates for every possible position/speed/acceleration-combination.

[dheerendra]

You can define the base class like the following.

class BaseMotorState : public QState
{
public:
BaseMotorState();

public slots :
void setMotoValues(int p, int s, int a);
virtual void doTask();

private :
int pos;
int speed;
int acc;
};

All the four states inherit from BaseMotoState. Based on the entered() and exit() signals of QState you can set the appropriate values. Implement doWork() method in each of your derived state. Call the doWork().. when you enter the state.

[kain]

Well, if I do it like this, I have to call 2 slots. The first one to set the parameters and the second one to transition into that QState.
Let's assume I got a Signal

void StartMovement(int pos, int speed, int acc)

and a transition

idleState->addTransition(this, &Wrapper::StartMovement, MovingState);

Is there any way to have these parameters available in the 'entered()'-Slot of QState? Of course I could call

setMotoValues(int p, int s, int a);

before emitting the signal 'StartMovement' but this does not look to me like a good pattern. Or is there no other solution?

[SGaist]

Where does this signal come from ?
What is Wrapper ?

[kain]

Wrapper in this Case is the 'CoverStateMachine' above.
For example this would be

I need a signal with parameters like this:

void StartMovement(int pos, int speed, int acc)

which triggers a transition like that

stateOpen->addTransition(this, &CoverStateMachine::StartMovement, stateMoving);

but in that stateMoving QState I need those parameters from that signal above.

[dheerendra]

addTransition will help only in transitioning the state and make the state enter. Before making the transition to new state, set the appropriate properties/methods of next state. From there is should continue. Idea is that State should have all the properties set work when it starts.

[MrShawn]

What @dheerendra is saying makes sense.... usually what i do is have a handler that oversees the execution of my state machine, which also holds the variables that will be used.

For example rather than inhereting from QStateMachine or QState i create a handler and have a function that builds my state machine. All the variables being worked with live in the scope of my handler class, and i have signals and slots in the handler class to do operations when states are entered and emit when it is time to change states. Here is some code from an example I did recently.

I posted a lot of code but hopefully it helps. I gave you the code in every slot that is connected to onEntry signal for each state, and then a little extra.

I read you said you have a state machine within a state machine. I suggest simplifying that down to using child states, it is effectively the same thing but allows you to have one state machine.

void MainHandler::buildStateMachine()
{
    stateRunning = new QState;
    stateError = new QFinalState;
    stateFinished = new QFinalState;
    stateSendCommand = new QState(stateRunning);
    stateWaitForArrival = new QState(stateRunning);
    stateDelay = new QState(stateRunning);
    stateRunning->setInitialState(stateSendCommand);

    stateRunning->addTransition(this,&MainHandler::t_Error,stateError);
    stateRunning->addTransition(this,&MainHandler::t_LastCommandExecuted,stateFinished);
    stateSendCommand->addTransition(this,&MainHandler::t_CommandSent,stateWaitForArrival);
    stateWaitForArrival->addTransition(this,&MainHandler::t_LocationReached,stateDelay);
    stateWaitForArrival->addTransition(this,&MainHandler::t_KeepWaiting,stateWaitForArrival);
    stateDelay->addTransition(this,&MainHandler::t_NextCommand,stateSendCommand);

    myStateMachine.addState(stateRunning);
    myStateMachine.addState(stateError);
    myStateMachine.addState(stateFinished);
   
    connect(stateRunning,&QState::entered,this,&MainHandler::slot_running);
    connect(stateSendCommand,&QState::entered,this,&MainHandler::slot_sendCommand);
    connect(stateWaitForArrival,&QState::entered,this,&MainHandler::slot_waitForArrival);
    connect(stateDelay,&QState::entered,this,&MainHandler::slot_delayStart);
    connect(stateError,&QState::entered,this,&MainHandler::slot_error);
    connect(stateFinished,&QState::entered,this,&MainHandler::slot_finished);
    connect(&myStateMachine,&QStateMachine::started,this,&MainHandler::slot_stateMachineStarted);
    connect(&myStateMachine,&QStateMachine::finished,this,&MainHandler::slot_stateMachineFinished);


    myStateMachine.setInitialState(stateRunning);
}

void MainHandler::slot_executeStateMachine()
{
    currentCommand.getById(Command::getAllCommandIDs().first());
    myStateMachine.start();
}

void MainHandler::slot_stateMachineStarted()
{
    qDebug() << "Started!";
    //currentCommand.getById(Command::getAllCommandIDs().first());
}

void MainHandler::slot_stateMachineFinished()
{
    qDebug() << "State Machine Finished!!";
}

void MainHandler::slot_running()
{
    qDebug() << "Running!";
}

void MainHandler::slot_sendCommand()
{
    if (currentCommand.getId() == -1)
        currentCommand.getById(Command::getAllCommandIDs().first());

    Position tmpPosition = myPositions.getPosition(currentCommand.getSavedPositionID());
    if (tmpPosition.id != -1)
    {
        currentPosition = tmpPosition;
        qDebug() << "Sending command for id" << currentCommand.getId();
        emit sig_executingCommand(currentCommand.getOrderNumber());
        qDebug() << currentPosition.getPosition(1) <<  currentPosition.getPosition(2) <<  currentPosition.getPosition(3) <<  currentPosition.getPosition(4) <<  currentPosition.getPosition(5);
        qDebug() << currentPosition.getPositions();
        qDebug() << currentCommand.toJSON().toJson(QJsonDocument::Compact);
        myConnection.write(currentCommand.toJSON().toJson(QJsonDocument::Compact)+"\r\n");
        myTimer.start();
        emit t_CommandSent();
    }
    else
    {
        emit t_Error();
    }

}

void MainHandler::slot_waitForArrival()
{
    //qDebug() << "Waiting...";

    bool done = true;
    QListIterator<Axis> iter(myAxisList);
    Axis A1(-1,0),A2(-1,0),A3(-1,0),A4(-1,0),A5(-1,0);
    while (iter.hasNext())
    {
        Axis tmpAxis = iter.next();
        switch (tmpAxis.axis) {
        case 1:
            //qDebug() << "got 1";
            A1 = tmpAxis;
            break;
        case 2:
            //qDebug() << "got 2";
            A2 = tmpAxis;
            break;
        case 3:
            //qDebug() << "got 3";
            A3 = tmpAxis;
            break;
        case 4:
            //qDebug() << "got 4";
            A4 = tmpAxis;
            break;
        case 5:
            //qDebug() << "got 5";
            A5 = tmpAxis;
            break;
        }
    }

    done = (determineIfAxisIsInPosition(A1) && determineIfAxisIsInPosition(A2) && determineIfAxisIsInPosition(A3) && determineIfAxisIsInPosition(A4) && determineIfAxisIsInPosition(A5));

    if (done)
    {
        emit t_LocationReached();
    }
    else if(myTimer.elapsed() < 5000)
    {
        QTimer::singleShot(100,this,&MainHandler::t_KeepWaiting);
    }
    else
        emit t_Error();
}

void MainHandler::slot_delayFinished()
{
    qDebug() << "Delay finished!";
    if(currentCommand.isLastCommand())
        emit t_LastCommandExecuted();
    else
    {
        currentCommand.getById(currentCommand.getNextCommandId());
        QTimer::singleShot(30,this,&MainHandler::t_NextCommand);
    }
}

void MainHandler::slot_delayStart()
{
    qDebug() << "Delay starting!";
    QTimer::singleShot(currentCommand.getMsDelay(),this,&MainHandler::slot_delayFinished);
}

void MainHandler::slot_finished()
{
    qDebug() << "Finished";
}

void MainHandler::slot_error()
{
    emit sig_Error("Error running command number: " + QString::number(currentCommand.getOrderNumber()));
    qDebug() << "Error!";
}