How to use one rxjava observable after previous is completed?

Question

I've two RxJava Observables and I get an arraylist from first observable and then use it to get data from another observable like this.

Observable<KarobarTvVod> observable1 = youtubeDataHelper.getTVData();
    observable1.subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .unsubscribeOn(Schedulers.io())
            .subscribe(new Subscriber<KarobarTvVod>() {
                @Override
                public void onCompleted() {

                }

                @Override
                public void onError(Throwable e) {
                    e.printStackTrace();
                }

                @Override
                public void onNext(KarobarTvVod karobarTvVod) {
                    Log.d(TAG, "onNext: size" + karobarTvVod.getEtag());
                    tvObjArrayList = new ArrayList<TVObj>();
                    for (int i = 0; i < karobarTvVod.getItems().size(); i++) {
                        TVObj tvObj = new TVObj();
                        tvObj.setVideoDate(karobarTvVod.getItems().get(i).getSnippet().getPublishedAt());
                        tvObj.setVideoIcon(karobarTvVod.getItems().get(i).getSnippet().getThumbnails().getHigh().getUrl());
                        tvObj.setVideoTitle(karobarTvVod.getItems().get(i).getSnippet().getTitle());
                        tvObj.setVideoID(karobarTvVod.getItems().get(i).getId().getVideoId());
                        tvObjArrayList.add(tvObj);
                    }


                }
            });



    Observable<YoutubeViews> observable2 = youtubeDataHelper.getTVDataViews(tvObjArrayList);
    observable2.subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .unsubscribeOn(Schedulers.io())
            .subscribe(new Subscriber<YoutubeViews>() {
                @Override
                public void onCompleted() {

                }

                @Override
                public void onError(Throwable e) {
                    Log.d(TAG, "onError: in 2nd obs");
                    e.printStackTrace();
                }

                @Override
                public void onNext(YoutubeViews youtubeViews) {
                    Log.d(TAG, "onNext: views" + youtubeViews.getEtag());
                    viewsList = new ArrayList<String>();
                    for (int i = 0; i < youtubeViews.getItems().size(); i++) {

                        viewsList.add(youtubeViews.getItems().get(i).getStatistics().getViewCount());
                    }
                    tvView.displayList(tvObjArrayList, viewsList);
                }
            });

This is just sample code, I need to pass the tvObjArrayList when it gets populated from 1st Observable to 2nd Observable, what is the best practice to do so ? And also I'm using for-loop inside the 1st Observable, is there a better way to achieve it using rxjava ? Thanks

Answer 1

You should use flatMap operator. It won't get much easier than that.

Observable<KarobarTvVod> observable1 = youtubeDataHelper.getTVData();
observable1.subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .unsubscribeOn(Schedulers.io())
        .flatMap(new Func1<KarobarTvVod, Observable<YoutubeViews>>() {
            @Override
            public Observable<YoutubeViews> call(KarobarTvVod karobarTvVod) {
                Log.d(TAG, "onNext: size" + karobarTvVod.getEtag());
                tvObjArrayList = new ArrayList<TVObj>();
                for (int i = 0; i < karobarTvVod.getItems().size(); i++) {
                    TVObj tvObj = new TVObj();
                    tvObj.setVideoDate(karobarTvVod.getItems().get(i).getSnippet().getPublishedAt());
                    tvObj.setVideoIcon(karobarTvVod.getItems().get(i).getSnippet().getThumbnails().getHigh().getUrl());
                    tvObj.setVideoTitle(karobarTvVod.getItems().get(i).getSnippet().getTitle());
                    tvObj.setVideoID(karobarTvVod.getItems().get(i).getId().getVideoId());
                    tvObjArrayList.add(tvObj);
                }
                return youtubeDataHelper.getTVDataViews(tvObjArrayList);
            }
        }).subscribe(new Subscriber<YoutubeViews>() {
            @Override
            public void onCompleted() {

            }

            @Override
            public void onError(Throwable e) {
                Log.d(TAG, "onError: in 1st or 2nd obs");
                e.printStackTrace();
            }

            @Override
            public void onNext(YoutubeViews youtubeViews) {
                Log.d(TAG, "onNext: views" + youtubeViews.getEtag());
                viewsList = new ArrayList<String>();
                for (int i = 0; i < youtubeViews.getItems().size(); i++) {

                    viewsList.add(youtubeViews.getItems().get(i).getStatistics().getViewCount());
                }
                tvView.displayList(tvObjArrayList, viewsList);
            }
        });