Missing listener which reports state changes in an "atomic" way

I have the following sample state machine:

  val machine = createStateMachine(name = "app") {
    initialState("init")
    state("main", childMode = ChildMode.PARALLEL) {
      state("main_screen") {
        initialState("idle")
      }
      state("bottom_bar") {
        initialState("bar_visible")
        state("bar_hidden")
      }
      state("bottom_sheet") {
        initialState("sheet_hidden")
        state("search")
        state("routing")
        state("bookmarks")
        state("more")
      }
    }

and the following listener:

  machine.addListener(object : StateMachine.Listener {
    override fun onStateChanged(newState: IState) {
      println("active states:\n${machine.activeStates().joinToString(",")}")
    }
  })

There are few problems with it. Before I list them I want to say that I think they are caused by the fact that this listener should simply have a different name, something like onStateEntered, because a “state change” usually means the machine arriving at the new state (or set of states) and is usually called after full transition has happened.

From the current name I expected it to behave as “active state change listener” and had the following problems:

1. When entering the main state this listener reports 3 separate state changes:
   • change to main_screen.idle
   • change to bottom_bar.bar_visible
   • change to bottom_sheet.sheet.hidden But the parallel state change is one change, i.e machine goes from init state to all 3 parallel states as one transaction. I mean internally it may do several onEntry in order, but to the user this should be reported as a single state change (it just so happens that the next state consists of 3 sub-states, but it’s still one state);
2. Also when used in non-parallel states, but with child states, this listener reports changes to “compound states”, but it should only report “leaf” states. That is if some event changes state from parent1.childA to parent1.parent2.parent3.childB, listener will be called with arguments parent2, parent3, childB while the actual “finalized” state changed only once, because single event moves machine from one state to another (=1 state change) and this listener should be called only once with argument childB. At least this is how all libs that I’ve used behave…
3. It has only one argument which doesn’t “feel” right in presence of parallel state feature, I’d expect active states set to be passed there…

Perhaps one solution to this is to rename the existing listener somehow, but I’d also like to be able to use the actual state change listener implemented sometime.

[nsk90]

I see that jetpack repo has 0.16.0, but maven central is still on 0.15.0 (reporting this in case it got out of sync somehow).

I will publish to maven central on next week

[nsk90]

Try this workaround for your sample:

                targetState = {
                    val activeChild = event.state.activeStates().single()
                    val data = (activeChild as DataState<Int>).data
                    if (data == 3) s2 else s3
                }

It is easy to get data from DataState and put it into FinishedState at the moment of generation on library side. But I am not sure that it will work without casts on client side. (at least with current design)

Yes, let’s create new issue. I think it can be done some way.