How to simply replace android AsyncTask with RX / Coroutines and return a value?

Issue

this method runs a database operation (returns a generated ID) and must be on background thread:

fun insert(note: Note): Long{ return noteDao.insert(note) }

Is there a way to implement it using RX / Coroutines? (without using the suspend keyword)

I currently use AsyncTask:

override fun insert(note: Note): Long {
    return InsertTask(this, noteDao).execute(note).get()
}

private class InsertTask(noteRepository: NoteRepository, private val noteDao: NoteDao) : AsyncTask<Note, Void, Long>() {

    override fun doInBackground(vararg note: Note): Long {
        return noteDao.insert(note[0])
    }

    override fun onPostExecute(generatedId: Long) {
        getTheId(generatedId)
    }

    private fun getTheId( id: Long): Long {
        return id
    }
}

Solution

With coroutines, it's pretty easy. But you will need coroutines support for Room.

Gradle dependency:

implementation "androidx.room:room-ktx:2.1.0"

Next, mark your methods in dao as suspend.

@Insert
suspend fun insert(note: Note): Long

I don't know how much info you have about coroutines, but it goes like that:

aCoroutineScope.launch(Dispatchers.IO){
 //to make analogy you are inside the do in backgroun here
  val id = dao.insert(note)
  withContext(Dispatchers.Main){
  //oh well you can call this onPostExecute :) 
  //do whatever you need with that selectId here
  handleIdOnTheMainThread(id)
  }
}

But I do insist not to use it with 0 information about coroutines.

About RxJava:

Room has also support for Rx, so please refer to this link.

Answered By - coroutineDispatcher