AndroidCoroutinesRetrofitMVVM

MainActivity

class MainActivity : AppCompatActivity() {

    lateinit var viewModel: ListViewModel
    private val countriesAdapter = CountryListAdapter(arrayListOf())

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

        viewModel = ViewModelProviders.of(this).get(ListViewModel::class.java)
        viewModel.refresh()

        countriesList.apply {
            layoutManager = LinearLayoutManager(context)
            adapter = countriesAdapter
        }

        observeViewModel()
    }

    fun observeViewModel() {
        viewModel.countries.observe(this, Observer {countries ->
            countries?.let {
                countriesList.visibility = View.VISIBLE
                countriesAdapter.updateCountries(it) }
        })

        viewModel.countryLoadError.observe(this, Observer { isError ->
            list_error.visibility = if(isError == "") View.GONE else View.VISIBLE
        })

        viewModel.loading.observe(this, Observer { isLoading ->
            isLoading?.let {
                loading_view.visibility = if(it) View.VISIBLE else View.GONE
                if(it) {
                    list_error.visibility = View.GONE
                    countriesList.visibility = View.GONE
                }
            }
        })
    }
}

ViewModel

class ListViewModel: ViewModel() {

    val countriesService = CountriesService.getCountriesService()
    var job: Job? = null
    val exceptionHandler = CoroutineExceptionHandler { coroutineContext, throwable ->
        onError("Exception: ${throwable.localizedMessage}")
    }

    val countries = MutableLiveData<List<Country>>()
    val countryLoadError = MutableLiveData<String?>()
    val loading = MutableLiveData<Boolean>()

    fun refresh() {
        fetchCountries()
    }

    private fun fetchCountries() {
        loading.value = true

        job = CoroutineScope(Dispatchers.IO + exceptionHandler).launch {
            val response = countriesService.getCountries()
            withContext(Dispatchers.Main) {
                if(response.isSuccessful) {
                    countries.value = response.body()
                    countryLoadError.value = null
                    loading.value = false
                } else {
                    onError("Error: ${response.message()}")
                }
            }
        }
    }

    private fun onError(message: String) {
        countryLoadError.value = message
        loading.value = false
    }

    override fun onCleared() {
        super.onCleared()
        job?.cancel()
    }

}