RxJava performing operation on a list and returning an observable

Question

I'm new to RxJava (specifically, RxJava2) and I'm having some trouble with what seems to be a relatively easy operation. I need to get some data from a db, iterate through the data (it is represented as a list), perform an operation on each item, wrap the data in another object and return. This is what I have so far:

mDataManager
    .getStuffList(id)
    .flatMapIterable(listOfStuff -> listOfStuff)
    .flatMap(item ->
         mDataManager
             .performCount(id, item.getTitle())
             .doOnNext(item::setCounter)
             .takeLast(1)
             .map(counter -> item))
    .toList()
    .toObservable()
    .flatMap(listOfStuff -> Observable.just(new StuffWrapper(listOfStuff));

The problem I'm having is that my data manager calls never complete. The idea was that whenever the underlying data changes, the UI changes as well. However, without completing those calls, toList() won't emit the event.

Answer 1

In RxJava 2, toList returns a Single: it's equivalent to an Observable with exactly one item. You can convert it to an Observable by adding .toObservable, but that isn't needed that often.

Regarding your other changes, what do you mean by whenever the underlying data changes? Does your data manager notify you on data changes?

Edit: if your mDataManager.getStuffList(id) call returns an Observable that emits multiple items (that is, it never completes but always emits the latest data set after a change), then you need to do something like this:

mDataManager
.getStuffList(id)
.flatMap(listOfStuff ->
    Observable
    .from(listOfStuff)
    .flatMap(item ->
         mDataManager
             .performCount(id, item.getTitle())
             .doOnNext(item::setCounter)
             .takeLast(1)
         .map(counter -> item)
         .toList()
    )
)
...