RxJava .autoConnect() example

AutoConnectExample.kt

import android.arch.lifecycle.ViewModel
import android.arch.lifecycle.ViewModelProviders
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import com.jakewharton.rxbinding3.view.clicks
import com.jakewharton.rxrelay2.PublishRelay
import com.mkorakin.clicker.R
import io.reactivex.Observable
import io.reactivex.android.schedulers.AndroidSchedulers
import io.reactivex.disposables.CompositeDisposable
import io.reactivex.observables.ConnectableObservable
import kotlinx.android.synthetic.main.activity_clicker.*

/**
 * An example for using a [ConnectableObservable] to host a stream in a [ViewModel].
 */
class MyViewModel : ViewModel() {

    private val viewModelDisposables = CompositeDisposable()

    val userInput = PublishRelay.create<Input>()

    val viewsState: Observable<ViewState> =

        // A stream of user input
        userInput

            // Transformed to a stream of view states
            .toViewState()

            // Last state emitted is replayed to new subscribers
            .replay(1)

            // An upstream connection is made on the first subscription
            // and shared with all future subscribers.
            .autoConnect(1) { upstreamConnection ->

                // Upstream disposable kept for later disposal.
                viewModelDisposables.add(upstreamConnection)
            }

    override fun onCleared() {
        viewModelDisposables.dispose()
        super.onCleared()
    }

    /**
     * Transform a stream of user events to a stream of updated view states.
     */
    private fun Observable<Input>.toViewState(): Observable<ViewState> =
        scan(ViewState(0)) { state, _ -> state.copy(clicksCount = state.clicksCount + 1) }
}

class AutoConnectExampleActivity : AppCompatActivity() {

    private val activityDisposables = CompositeDisposable()

    private val viewModel: MyViewModel by lazy {
        ViewModelProviders.of(this).get(MyViewModel::class.java)
    }

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

        button
            .clicks()
            .map { Input }
            .subscribe(viewModel.userInput::accept)
            .let(activityDisposables::add)

        viewModel
            .viewsState
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(::render)
            .let(activityDisposables::add)
    }

    private fun render(viewState: ViewState) {
        button.text = viewState.clicksCount.toString()
    }

    override fun onDestroy() {
        activityDisposables.dispose()
        super.onDestroy()
    }
}

object Input

data class ViewState(val clicksCount: Int)