class ActivityA : Activity() {

    val textView: TextView = findViewById(android.R.id.text1) as TextView

    val a = BehaviorSubject(1)
    val b = BehaviorSubject(2)
    val c = BehaviorSubject(3)

    lateinit var subscription: Subscription

    override fun onStart() {
        super.onStart()
        subscription = Observable.combineLatest(a, b, c) { a, b, c -> a * b * c }
                .map { it.toString() }
                .subscribe {
                    textView.text = it
                }

        //here i change values
        b.onNext(5)
        a.onNext(1)
    }

    override fun onStop() {
        super.onStop()
        subscription.unsubscribe()
    }
}