rxjava with for each loop

Question

I am trying to get the data from local db by each content asyncrounous,but the issue is that I want to get the data by the order that I retrieve,at first the data for the first conent,than the second etc.,currently I am getting the data in wrong order every time I run the code ,how can I achieve this?

 for (Content content : contents) {
                scoreCardDisposable = AppManagers.getContentManager()
                        .getScoreCardsAndUpdate(content.getId())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe(scoreCards -> {
                           ...
                        });
                compositeDisposable.add(scoreCardDisposable);

           }

You'll need to use from iterable which is the equivalent of a for loop in rx java, once you get that you can use flatmap for the rest of it or you can probably skip the flatmap also. — Jude Fernandes
– Jude Fernandes, Commented May 23, 2018 at 12:57

Dmitry · Accepted Answer · 2018-05-23 14:59:59Z

4

To make an observable stream from a List<> you can use Observable.fromIterable operator:

compositeDisposable.add(Observable.fromIterable(contents)
            .flatMap(content -> {
                return AppManagers.getContentManager()
                        .getScoreCardsAndUpdate(content.getId());
            })
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(scoreCards -> {
                ...
            }));

UPD:

You can use a zip operator to combine content with the getScoreCardsAndUpdate result in custom object:

class Result {
    private String content;
    private String result;

    public Result(String content, String result) {
        this.content = content;
        this.result = result;
    }

    public String getContent() {
        return content;
    }

    public String getResult() {
        return result;
    }
}

public Observable<String> getScoreCardsAndUpdate(String content) {
    return Observable.just("result = " + content);
}

@Test
public void test() {
    List<String> contents = Arrays.asList("1", "2", "3", "4");

    Observable.fromIterable(contents)
            .flatMap(content -> {
                return Observable.zip(Observable.just(content), 
                        getScoreCardsAndUpdate(content), Result::new);
            })
            .subscribe(scoreCards -> {
                System.out.println("content = " + scoreCards.getContent() + 
                        ", " + scoreCards.getResult());
            });
}

edited May 23, 2018 at 14:59

answered May 23, 2018 at 14:24

Dmitry

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1 Comment

Katy Colins Over a year ago

Thx,can you please tell me how can I get content reference in subscribe ?

Suhaib Roomy · Accepted Answer · 2018-05-23 13:02:38Z

2

You will have to process all the items in a single thread. You can achieve this by adding a scheduler in rxjava2

.subscribeOn(Schedulers.single())

Your code should be

for (Content content : contents) {
            scoreCardDisposable = AppManagers.getContentManager()
                    .getScoreCardsAndUpdate(content.getId())
                    .observeOn(AndroidSchedulers.mainThread())
                    .subscribeOn(Schedulers.single())
                    .subscribe(scoreCards -> {
                       ...
                    });
            compositeDisposable.add(scoreCardDisposable);

       }

answered May 23, 2018 at 13:02

Suhaib Roomy

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2 Comments

Katy Colins Over a year ago

in getScoreCardsAndUpdate I already use subscribeOn(getIOScheduler()),should I change it?

Suhaib Roomy Over a year ago

yeah you will have to change it to any serial schedular so that your task gets executed one by one

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