How to dispose of disposable in RxJava2.0

Question

I'm new to Rx world and I've seen multiple example of how to dispose of a Disposable but I don't quite understand the difference. I'm using RxJava 2.0 (v2.2.17) and RxAndroid (v2.1.1).

My question is what's the difference between case 1 and case 2 ? Which one of those two cases to prefer in your application ?

Case 1:

private val compositeDisposable: CompositeDisposable = CompositeDisposable()

adsApiService.getVideos()
        .subscribeOn(Schedulers.io())
        .observeOn( AndroidSchedulers.mainThread())
        .subscribe(
            { v -> Log.d("video", v.toString()) },
            { e -> Log.d("video", e.toString()); compositeDisposable.dispose() },
            { compositeDisposable.dispose() },
            { disposable -> compositeDisposable.add(disposable)}
        )
}

Case 2:

class MainActivity : AppCompatActivity() {

    private var compositeDisposable: CompositeDisposable? = CompositeDisposable()

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

        compositeDisposable?.add(api.getVideosAds())
    }

    override fun onDestroy(){
        super.onDestroy()
        compositeDisposable?.dispose()
    }

}

Answer 1

Personally? Neither.

You should learn how to use ViewModels, and keep your CompositeDisposable there, and clear it in onCleared() method.

Also, there are some problems with your examples:

Case 1

You should simply add disposable to compositeDisposable, not sure why you pass 2 additional lambdas to subscribe:

compositeDisposable += adsApiService.getVideos()
  .subscribeOn(Schedulers.io())
  .observeOn( AndroidSchedulers.mainThread())
  .subscribe(
    { v -> Log.d("video", v.toString()) },
    { e -> Log.d("video", e.toString()) }
  )

In this case, you actually don't clear correctly the compositeDisposable, because it's not attached to any lifecycle (Activity, Fragment, or ViewModel)

Case 2

No need for question mark in statement:

private var compositeDisposable: CompositeDisposable? = CompositeDisposable()

This example is semantically correct, although api should be hidden in ViewModel (MVVM architecture) or Presenter (MVP architecture), or any architecture. Having everything in view class (MainActivity) is terrible practice and is extra hard to maintain.