Medium articles - MVI+FSM

TimerViewModel.kt

class TimerViewModel : ViewModel(), ContainerHost<TimerUiState, Nothing> {

    override val container = viewModelScope.container<TimerUiState, Nothing>(TimerUiState())
    private val stateMachine = StateMachine.create<TimerState.State, TimerState.Event, TimerState.SideEffect> {
        initialState(TimerState.State.Idle)

        state<TimerState.State.Idle> {
            on<TimerState.Event.OnSetTimer> {
                transitionTo(TimerState.State.SettingTimer, TimerState.SideEffect.SetTimer)
            }
        }
    
        state<TimerState.State.SettingTimer> {
            on<TimerState.Event.OnTimerSet> {
                transitionTo(TimerState.State.Idle, TimerState.SideEffect.TimerReady(it.value))
            }
        }

        onTransition {
            val validTransition = it as? StateMachine.Transition.Valid ?: return@onTransition
            when (val effect = validTransition.sideEffect as TimerState.SideEffect) {
                is TimerState.SideEffect.SetTimer -> intent { reduce { state.copy(isSettingTimer = true, isCountingDown = false, isRestarting = false) } }
                is TimerState.SideEffect.TimerReady -> intent { reduce { TimerUiState(effect.value) } }
            }
        }
    }

    fun settingTime() {
        stateMachine.transition(TimerState.Event.OnSetTimer)
    }

    fun setTime(seconds: Int) {
        stateMachine.transition(TimerState.Event.OnTimerSet(seconds))
    }
}

//Collecting state changes in the View
@Composable
fun TimerScreen(viewModel: TimerViewModel) {
    with(viewModel.collectAsState().value) { /*...*/ }
}