How to get all data in one column or more using room + rxjava and convert it to List<String> or Cursor to display it on UI i.e Recyclerview?

Question

I was just making simple Notes app in order to understand Room and Rxjava (and java).

Entity

@Entity
public class Notes {
    @PrimaryKey(autoGenerate = true)
    public long id;
    String title;
    String notes;}

Dao

@Query("SELECT * FROM Notes")
    Flowable<List<OnlyNotes>> getAllNotes();
    public class OnlyNotes {
        String notes;
    }

MainActivity:

    static List<String> notes;
    public Flowable<List<NotesDao.OnlyNotes>> initialize(){
        return (Flowable<List<NotesDao.OnlyNotes>>) notesDao.getAllNotes()
                .observeOn(AndroidSchedulers.mainThread());
    }

onCreate()

notes = (List<String>) initialize();//for RecyclerViewAdapter

FATAL EXCEPTION: main

Caused by: java.lang.ClassCastException: io.reactivex.internal.operators.flowable.FlowableObserveOn cannot be cast to java.util.List

Can you please explain me what is wrong with my code and what's the best practice of doing what I'm trying to do? I will be glad to any answer.

Answer 1

Replace Flowable<> with Observable<> in Dao and use code below. For Flowable you have to use Subscriber inside subscribe() method and override its methods. this hopefully should clarify your understanding of rxjava if you skipped some topics as I did.

db.notesDao().getAllNotes().subscribeOn(Schedulers.computation()).observeOn(AndroidSchedulers.mainThread()).subscribe(new Observer<List<NotesDao.OnlyNotes>>() {
        @Override
        public void onSubscribe(@NonNull Disposable d) {
           

        }

        @RequiresApi(api = Build.VERSION_CODES.N)
        @Override
        public void onNext(@NonNull List<NotesDao.OnlyNotes> onlyNotes) {
            if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                notes.addAll(onlyNotes.stream().map(objects -> objects.notes).collect(Collectors.toList()));
            }else {
                for (NotesDao.OnlyNotes onlyNotes1 : onlyNotes) {
                    notes.add(onlyNotes1.notes);
                }
            }
        }

        @Override
        public void onError(@NonNull Throwable e) {

        }

        @Override
        public void onComplete() {

        }
    });