stopwatch_activity.kt

class StopwatchActivity : FragmentActivity() {

    private val disposables = CompositeDisposable()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.stopwatch_activity)

        val renderView = StopwatchRenderView(findViewById(R.id.activity_content))
        val renderModels: Observable<StopwatchRenderModel> = 
            StopwatchFormula().start(Unit)
        disposables.add(renderModels.subscribe(renderView.renderer::render))
    }

    override fun onDestroy() {
        disposables.clear()
        super.onDestroy()
    }
}