RxJava2 toList() never emits

问题

So I have following Disposable which doesn't work. I am using Room to get all rows from a table as a list, map each of them to something and create a list and then it doesn't continue from there.

storedSuggestionDao
    .getSuggestionsOrderByType() //Flowable
    .doOnNext(storedSuggestions -> Timber.e("storedSuggestions: " + storedSuggestions)) //this work
    .flatMapIterable(storedSuggestions -> storedSuggestions)
    .map(Selection::create) ))
    .doOnNext(selection -> Timber.e("Selection: " + selection)) // works
    .toList()
    .toObservable() // nothing works after this...
    .doOnNext(selections -> Timber.d("selections: " + selections))
    .map(SuggestionUiModel::create)
    .doOnNext(suggestionUiModel -> Timber.d("suggestionUiModel: " + suggestionUiModel))
    .subscribe();

回答1:

These types of data sources from 3rd parties are usually infinite sources but toList() requires a finite source. I guess you wanted to process that collection of storedSuggestions and keep it together. You can achieve this via an inner transformation:

storedSuggestionDao
.getSuggestionsOrderByType() //Flowable
.doOnNext(storedSuggestions -> Timber.e("storedSuggestions: " + storedSuggestions)) //this work
// -------------------------------------
.flatMapSingle(storedSuggestions -> 
    Flowable.fromIterable(storedSuggestions)
    .map(Selection::create)
    .doOnNext(selection -> Timber.e("Selection: " + selection))
    .toList()
)
// -------------------------------------
.doOnNext(selections -> Timber.d("selections: " + selections))
.map(SuggestionUiModel::create)
.doOnNext(suggestionUiModel -> Timber.d("suggestionUiModel: " + suggestionUiModel))
.subscribe();

回答2:

I think in your case you don't need to call .toObserable()

It should be like this

storedSuggestionDao
.getSuggestionsOrderByType() //Flowable
.doOnNext(storedSuggestions -> Timber.e("storedSuggestions: " + storedSuggestions)) //this work
.flatMapIterable(storedSuggestions -> storedSuggestions)
.map(Selection::create) ))
.doOnNext(selection -> Timber.e("Selection: " + selection)) // works
.toList() // you don't have to call .toObserable()
.map(SuggestionUiModel::create)
.subscribe();

回答3:

The problem is storedSuggestionDao.getSuggestionsOrderByType() //Flowable

is a hot stream. toList still waits for upstream to complete

来源：https://stackoverflow.com/questions/47327070/rxjava2-tolist-never-emits

标签

android

rx-java2

android-room