CatModel!

MainViewModel.kt

class MainViewModel : ViewModel() {

    private val compositeDisposableOnDestroy = CompositeDisposable()
    private var latestCatCall: Disposable? = null
    // the list that will be observed by the activity
    val bunchOfCats = MutableLiveData<List<NetCat>>()
    // the error message observed
    val errorMessage = MutableLiveData<String>()

    // the API call
    fun getSomeCats() {
        // initialising the repository class with the necessary information
        val catsRepository = CatsRepository(serverUrl, BuildConfig.DEBUG, apiKey)

        // stopping the last call if it's already running (optional)
        latestCatCall?.dispose()

        // perform the API call
        // asking for 10 cats. Don't care in what category so just passing null
        latestCatCall =
            catsRepository.getNumberOfRandomCats(10, null).subscribeOn(Schedulers.io())
                .doOnSubscribe {
                    compositeDisposableOnDestroy.add(it)
                }
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe { result ->
                    when {
                        result.hasError() -> result.errorMessage?.let {
                            // anyone who observes this will be notified of the change automatically
                            errorMessage.postValue("Error getting cats $it")
                        }
                            ?: run {
                                // anyone who observes this will be notified of the change automatically
                                errorMessage.postValue("Null error :(")
                            }
                        result.hasCats() -> result.netCats?.let {
                            // anyone who observes this will be notified of the change automatically
                            bunchOfCats.postValue(it)
                            // clearing the error if it existed (hacky and optional)
                            errorMessage.postValue("")
                        }
                            ?: run {
                                // anyone who observes this will be notified of the change automatically
                                errorMessage.postValue("Null list of cats :(")
                            }
                        else -> {
                            // anyone who observes this will be notified of the change automatically
                            errorMessage.postValue("No cats available :(")
                        }
                    }
                }
    }

    // clearing the collection of disposables = no memory leaks no matter what
    override fun onCleared() {
        compositeDisposableOnDestroy.clear()
        Log.d("TAG", "Clearing ViewModel")
        super.onCleared()
    }
}

Hi! Thanks a lot for the awesome article on Medium, sir! Could you please tell how are you initialize CatsRepository(serverUrl, BuildConfig.DEBUG, apiKey) when the class has no such fields. And how could you reinitialize variable latestCatsCall, earlier declared val (final)?

Hey, thanks for the kind words :)
You can find the CatsRepository class here.
In the constructor it has these 3 fields declared (lines 5,6 and 7).
The latestCatCall: Disposable variable is a var (on line 4 of this file). So it can be changed at any time.