Gist 2 - Android example

ApiService.kt

class ApiService {

    fun requestDataFromBackend(): Observable<MyRawDataModel> {
        return BackendAPI().returnSomeDummyData()
    }

    fun readCachedUserName(rawDataModel: MyRawDataModel) : Observable<Pair<MyRawDataModel, String>> {
        val cachedUserName = PreferenceManager.getDefaultSharedPreferences(MyApplication.INSTANCE).getString("USER_NAME", "") ?: ""
        return Observable.just(Pair(rawDataModel, cachedUserName))
    }
}

BackendAPI.kt

class BackendAPI {

    fun returnSomeDummyData(): Observable<MyRawDataModel> {
        return Observable.just(MyRawDataModel(123, "Bobi", "Davis", 50))
    }
}

MyActivity.kt

class MyActivity: AppCompatActivity(), MyPresenter.View {

    private val presenter = MyPresenter()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)

        presenter.setView(this)
        presenter.requestData(ApiService(), resources)
    }

    override fun drawViews(viewModel: MyViewModel) {
        //Unused at the moment, but could be used to display some data
    }

    override fun showLoader(show: Boolean) {
        //Unused at the moment, but could be used to show or hide screen loader
    }
}

MyPresenter.kt

class MyPresenter {

    private lateinit var view: View

    interface View {

        fun drawViews(viewModel: MyViewModel)

        fun showLoader(show: Boolean)

    }

    fun setView(view: View) {
        this.view = view
    }

    fun requestData(service: ApiService, resources: Resources) {
        service.requestDataFromBackend()
            .observeOn(Schedulers.io())
            .subscribeOn(AndroidSchedulers.mainThread())
            .flatMap { service.readCachedUserName(it) }
            .subscribe { covertDataModelAndDraw(it, resources) }
    }

    private fun covertDataModelAndDraw(pair: Pair<MyRawDataModel, String>, resources: Resources) {
        val fullName = String.format(resources.getString(R.string.full_name_pattern), pair.first.firstName, pair.first.lastName)
        val userName = pair.second
        val age = pair.first.age
        val message = resources.getString(R.string.my_message)

        val viewModel = MyViewModel(fullName, userName, age, message)

        view.drawViews(viewModel)
    }
}

MyRawDataModel.kt

data class MyRawDataModel(@SerializedName("id") val id: Int,
                          @SerializedName("firstName") val firstName: String,
                          @SerializedName("lastName") val lastName: String,
                          @SerializedName("age") val age: Int)

data class MyViewModel(private val name: String,
                       private val userName: String,
                       private val age: Int,
                       private val message: String)