http://reactivex.io/RxJava/javadoc/io/reactivex/disposables/CompositeDisposable.html

In this lesson you will learn how CompositeDisposable simplifies dealing with multiple Disposables.

https://caster.io/lessons/rxjava-2-compositedisposable

https://github.com/shadowmanpat/RxJava2Caster.io

// adding an Observable to the disposable
disposables.add(sampleObservable()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeWith(new DisposableObserver<String>() {
                    @Override
                    public void onComplete() {
                    }

                    @Override
                    public void onError(Throwable e) {
                    }

                    @Override
                    public void onNext(String value) {
                    }
                }));

    static Observable<String> sampleObservable() {
        return Observable.defer(new Callable<ObservableSource<? extends String>>() {
            @Override
            public ObservableSource<? extends String> call() throws Exception {
                // Do some long running operation
                SystemClock.sleep(2000);
                return Observable.just("one", "two", "three", "four", "five");
            }
        });
    }                


// Using clear will clear all, but can accept new disposable
disposables.clear(); 
// Using dispose will clear all and set isDisposed = true, so it will not accept any new disposable
disposables.dispose();

ext {
  rxjava2_version = "2.1.7"
}
dependencies {
  implementation "io.reactivex.rxjava2:rxjava:${rxjava2_version}"
}

class AndroidDisposable {
    private var compositeDisposable: CompositeDisposable? = null

    fun add(disposable: Disposable) {
        if (compositeDisposable == null) {
            compositeDisposable = CompositeDisposable()
        }
        compositeDisposable?.add(disposable)
    }

    fun dispose() {
        compositeDisposable?.dispose()
        compositeDisposable = null
    }
}

class MainActivity : AppCompatActivity() {
    private disposable = AndroidDisposable()

    override fun onStart() {
        super.onStart()
        disposable.add(/* Some disposable */)
    }

    override fun onStop() {
        disposable.dispose()
        super.onStop()
    }
}

operator fun AndroidDisposable.plusAssign(disposable: Disposable) {
    add(disposable)
}

fun Disposable.addTo(androidDisposable: AndroidDisposable): Disposable
    = apply { androidDisposable.add(this) }

val texts = listOf("1", "2", "3")

// Operator
disposable += Observable.fromIterable(texts)
    .map { it.toInt(10) }
    .reduce { t1, t2 -> t1 + t2 }
    .subscribe()

// or
Observable.fromIterable(texts)
    .map { it.toInt(10) }
    .reduce { t1, t2 -> t1 + t2 }
    .subscribe()
    .addTo(disposable)