MVI Example 2 -- StateModel

MainActivity.kt

class MainActivity : AppCompatActivity(R.layout.activity_main) {

    @Inject
    lateinit var viewModel: MainActivityViewModel

    private var isInitialised: Boolean = false

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        init()
    }

    private fun init() {
        if (!isInitialised) {

            lifecycleScope.launch {
                viewModel
                    .state
                    .collect(::render)
            }

            viewModel
                .send(
                    MainActivityView.Event.OnViewInitialised
                )
            isInitialised = true
        }
    }

    private suspend fun render(state: MainActivityView.State): Unit =
        when (state.renderEvent) {
            MainActivityView.RenderEvent.Idle -> Unit
            is MainActivityView.RenderEvent.DisplayText ->
                renderDisplayText(text = state.renderEvent.text)
        }

    private fun renderDisplayText(text: String) {
        // render text
    }

}

MainActivityView.kt

object MainActivityView {

    @ExperimentalCoroutinesApi
    class StateModel(initialState: State = State()) {

        private val _state = MutableStateFlow(initialState)
        val state: StateFlow<State> get() = _state

        fun setState(newState: State) {
            _state.value = newState
        }

        fun setRenderState(renderEvent: RenderEvent) {
            _state.value = _state.value.copy(renderEvent = renderEvent)
        }
    }

    data class State(
        val renderEvent: RenderEvent = RenderEvent.Idle
    )

    sealed class Event {
        object OnViewInitialised : Event()
        data class OnButtonClicked(val idOfItemClicked: Int) : Event()
    }

    sealed class RenderEvent {
        object Idle : RenderEvent()
        data class DisplayText(val text: String) : RenderEvent()
    }

}

MainActivityViewModel.kt

class MainActivityViewModel @Inject constructor(
    private val state: MainActivityView.StateModel,
    private val messageOfTheDayRepository: MessageOfTheDayRepository
) {

    val state: StateFlow<MainActivityView.State>
        get() = stateModel.state

    fun send(event: MainActivityView.Event): Unit {
        viewModelScope.launch {
            reduce(event = event)
        }
    }

    private suspend fun reduce(event: MainActivityView.Event): Unit =
        when (event) {
            MainActivityView.Event.OnViewInitialised -> onViewInitialisedEvent()
            MainActivityView.Event.OnButtonClicked -> onButtonClickedEvent(event.idOfItemClicked)
        }

    private suspend fun onViewInitialisedEvent() {

        val motd: String = withContext(Dispatchers.IO) {
            messageOfTheDayRepository.getMOTD()
        }

        val renderEvent = MainActivityView.RenderEvent.DisplayText(text = motd)
        stateModel.setRenderEvent(renderEvent = renderEvent)
    }

    private fun onButtonClickedEvent(idOfItemClicked: Int) {
        // do something to handle click
        println("item clicked: $idOfItemClicked")
    }

}