[Interest] SCXML and datamodel sharing in Qt Quick and C++

[Ulf Hermann]

> 1. I use scxml compiler and expose compiled machine to Qt Quick.
> 2. I use ecmascript as datamodel type. I create data entries in *.scxml file.
> 3. I need to repeat those values on Qt Quick side and assign to StateMachine.initialValues so that they will be reset everytime machine starts - without it even when default values for data entries in scxml file are set - they are not reset.
> 4. To change model entries (and the same evaluate transition conditions that have those entries in cond attribute) I need to send custom, external event from Qt Quick (let's call it DATAMODEL.CHANGE), which contains dictionary. In scxml I handle that event by assigning all entries of that dictionary to  corresponding datamodel entries.

You cannot really stop and "deinitialize" a statemachine. If you set running to false, it is paused and will continue from the point where it stopped when you set it to true again. So, in order to reset the data model you have to destroy and recreate the state machine.

> Is it possible by any way to define model once and share it between scxml state machine, Qt Quick, C++ side?
QScxmlStateMachine has a property "dataModel" which can be accessed from the outside and you can manipulate properties on that. However, the respective methods are not Q_INVOKABLE, so for QML you'll have to wrap that in some other type. The lack of proper QML API for this may be a bug. In any case, sending an event to the state machine is a cleaner way to do this, as otherwise the machine will not know that the value has changed and will not react to the change until some other event happens.

Ulf