PostRepo-BoundaryCallback.kt

interface PostRepository {
   fun getFeeds(): Observable<PagedList<Post>>
}

class PostRepositoryImpl : PostRepository {

  private val remoteDataSource: PostApiService by inject()
  private val localDataSource: PostDao by inject()

  private val postBoundaryCallback: postBoundaryCallback by inject()

   override fun getFeeds(): Observable<PagedList<Post>> {
       val dataSource = localDataSource.getPostList()
       val pagedListConfig = PagedList.Config.Builder()
           .setPageSize(10)
           .setPrefetchDistance(4)
           .build()
       return RxPagedListBuilder(dataSource, pagedListConfig)
           .setBoundaryCallback(postBoundaryCallback)
           .buildObservable()
   }
}