The NetoworkBoundSource which use RxJava instead of LiveData.

NetworkBoundSource.kt

import io.reactivex.Observable
import io.reactivex.android.schedulers.AndroidSchedulers
import io.reactivex.schedulers.Schedulers
import retrofit2.Response

abstract class NetworkBoundResource<ResultType, RequestType> {

    private var result: Observable<Resource<ResultType>>

    init {
        result = loadFromLocal().flatMap {
            if (shouldFetch(it)) {
                fetchFromNetwork()
            } else {
                Observable.just(Resource.success(it))
            }
        }.startWith(Resource.loading(null))
    }

    private fun fetchFromNetwork(): Observable<Resource<ResultType>>? {
        return createCall().subscribeOn(Schedulers.io()).flatMap {
            Observable.just(it.body()?.data)
        }.doOnNext {
            if (it != null) {
                saveCallResult(it)
            }
        }.observeOn(AndroidSchedulers.mainThread()).doOnError {
            onFetchFailed()
        }.observeOn(Schedulers.io()).flatMap {
            loadFromLocal()
        }.observeOn(AndroidSchedulers.mainThread()).map {
            Resource.success(it)
        }.onErrorReturn {
            Resource.error("", null)
        }
    }

    fun asObservable(): Observable<Resource<ResultType>> {
        return result
    }

    open fun onFetchFailed() {}

    abstract fun shouldFetch(data: ResultType?): Boolean

    abstract fun loadFromLocal(): Observable<ResultType>

    abstract fun createCall(): Observable<Response<ResponseData<RequestType>>>

    abstract fun saveCallResult(item: RequestType)
}

Resource.kt

data class Resource<out T>(val data: T?, val message: String?) {
    companion object {
        fun <T> success(data: T?): Resource<T> {
            return Resource(data, null)
        }

        fun <T> error(msg: String, data: T?): Resource<T> {
            return Resource(data, msg)
        }

        fun <T> loading(data: T?): Resource<T> {
            return Resource(data, null)
        }
    }
}

ResponseData.kt

data class ResponseData<T>(
    var data: T?,
    var code: Int,
    var message: String?
)