Throttle KeyDown Events from MainActivity using Rx

throttlesample.kt

class MyActivity : AppCompatActivity() {

    private val emitter = KeyEventEmitter()

    private var subscription by Delegates.notNull<CompositeDisposable>()

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

        subscription = CompositeDisposable()

        createKeyObservable(emitter)
            .subscribe({ (keyCode, event) ->

                // latest keyevent  if there is one only every 100 ms
                Log.v("keyevent", "$keyCode $event")

            }, Throwable::printStackTrace)
            .addTo(subscription)
    }

    override fun onDestroy() {
        if (!subscription.isDisposed)
            subscription.dispose()
        super.onDestroy()
    }

    override fun onKeyDown(keyCode: Int, event: KeyEvent?): Boolean {
        emitter.onKeyDown(keyCode, event)
        return super.onKeyDown(keyCode, event)
    }
}

class KeyEventEmitter {

    internal var keyDown: ((keyCode: Int, event: KeyEvent?) -> Unit)? = null

    fun onKeyDown(keyCode: Int, event: KeyEvent?) {
        keyDown?.invoke(keyCode, event)
    }
}

fun createKeyObservable(keyEmitter: KeyEventEmitter) = BehaviorSubject.create<Pair<Int, KeyEvent?>> { emitter ->

    if (emitter.isDisposed)
        return@create

    keyEmitter.keyDown = { keyCode, event ->
        emitter.onNext(keyCode to event)
    }

}.doOnDispose { keyEmitter.keyDown = null }
    .throttleLatest(100, TimeUnit.MILLISECONDS)
    .observeOn(AndroidSchedulers.mainThread())