GetArtistEventsAsyncTask.kt

// Somewhere on the UI thread
class MyActivity : Activity {
  //...
  
  fun getData() {
    showProgress()
    GetArtistEvents(database, api, sharedPreferences).execute(artist)
  }
  
}

class GetArtistEvents(val database: BandsInTownDatabase, val api: BandsInTownApi, val sharedPreferences: SharedPreferences) :
        AsyncTask<Artist, Void, List<ArtistEvent>>() {
        override fun doInBackground(vararg artist: Artist): List<ArtistEvent> {
            // Check if data has been stored over an hour ago from now
            if (RepositoryUtil.isCacheStale(sharedPreferences, "ArtistEvent", artist.first().name, TimeUnit.HOURS.toSeconds(1))) {
                // Reset the cache time to "now"
                RepositoryUtil.resetCache(sharedPreferences, "ArtistEvent", artist.first().name)
                // Call webservice synchronously
                val freshEvents =  api.findArtistEvents(artist.first().name).execute().body()
                // Update/Insert events in database 
                bandsInTownDatabase.artistEventDao().upsert(freshEvents)
            }
            return database.artistEventDao().getEventsByArtistId(artist.first().id)
        }
                
        override fun onPostExecute(result: List<ArtistEvent>) {
            hideProgress()
            showData(result)
        }
}

// Retrofit web service interface
interface BandsInTownApi {
    @GET("/artists/{artistName}/events")
    fun findArtistEvents(
        @Path("artistName") artistName: String
    ): Call<List<ArtistEventResponse>>
}