MVI -- Example 1 -- ConflatedBroadcastChannel

MainActivity.kt

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

    @Inject
    lateinit var viewModel: MainActivityViewModel

    @Inject
    lateinit eventChannel: ConflatedBroadcastChannel<MainActivityView.Event>

    private var isInitialised: Boolean = false

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

        init()
    }
    
    private fun init() {
        if (!isInitialised) {
            
            lifecycleScope.launch {
                viewModel()
                    .flowOn(
                        Dispatchers.IO
                    ).collect(::render)
            }

            eventChannel
                .offer(
                    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 {

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

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

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

MainActivityViewModel.kt

class MainActivityViewModel constructor(
    private var state: MainActivityView.State = MainActivityView.State(),
    private val eventChannel: ConflatedBroadcastChannel<MainActivityView.Event>,
 ) {

    suspend fun invoke(): Flow<MainActivityView.State> =
        eventChannel
            .asFlow()
            .flatMapLatest { event: MainActivityView.Event ->
                reduce(event)
            }

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

    private fun onViewInitialisedEvent(): Flow<MainActivityView.State> = flow 
        val renderEvent = MainActivityView.RenderEvent.DisplayText(text = "hello world")
        state = state.copy(renderEvent = renderEvent)
        emit(state)
    }

    private fun onButtonClickedEvent(idOfItemClicked: Int): Flow<MainActivityView.State> = flow 
        // do something to handle click
        println("item clicked: $idOfItemClicked")
        emit(state)
    }

}