RxJava Load items on demand

Question

I want to load the next item(s) when some other observable emits a new item (a trigger).

This is the code that emits the items:

public Observable<Item> get() {
    return idApi.get().flatMap(new Function<List<String>, ObservableSource<String>>() {
        @Override
        public ObservableSource<String> apply(@NonNull List<String> ids) throws Exception {
            return Observable.fromIterable(ids);
        }
    }).flatMap(new Function<String, ObservableSource<Item>>() {
        @Override
        public ObservableSource<Item> apply(@NonNull final String id) throws Exception {
            return dataApi.get(id).map(new Function<Data, Item>() {
                @Override
                public Item apply(@NonNull Data data) throws Exception {
                    return new Item(data , id);
            });
        }
    });
}

Trigger Observable:

RxView.clicks(view.findViewById(R.id.button_more)).debounce(500, TimeUnit.MILLISECONDS);

The only way I could get around this was using a Subject and holding a reference to a list of ids which wasn't elegant and didn't seem reactive.

Edit: This is my solution so far, but I had to subscribe to trigger event directly. I don't consider it elegant.

@Override
public Observable<Item> get(final Observable<Object> trigger) {
    final PublishSubject<Item> subject = PublishSubject.create();
    return idApi.get().flatMap(new Function<List<String>, ObservableSource<Queue<String>>>() {
        @Override
        public ObservableSource<Queue<String>> apply(@NonNull List<String> ids) throws Exception {
            final Queue<String> q = new LinkedList<>(ids);
            return Observable.just(q);
        }
    }).flatMap(new Function<Queue<String>, ObservableSource<Item>>() {
        @Override
        public ObservableSource<Item> apply(@NonNull final Queue<String> ids) throws Exception {
            trigger.subscribeOn(AndroidSchedulers.mainThread()).subscribe(new Consumer<Object>() {
                @Override
                public void accept(@NonNull Object o) throws Exception {
                    if (ids.size() > 0) {
                        final String id = ids.poll();
                        dataApi.get(id).map(new Function<Data, Item>() {
                            @Override
                            public Item apply(@NonNull Data data) throws Exception {
                                return new Item(data, id) l
                            }
                        }).subscribe(new Consumer<Item>() {
                            @Override
                            public void accept(@NonNull Item item) throws Exception {
                                subject.onNext(item);
                            }
                        });
                    } else {
                        subject.onComplete();

                    }
                }
            });
            return subject;
        }
    });
}

Answer 1

Use zip

public Observable<Item> get(View v) {
    return idApi.get().flatMap(new Function<List<String>, ObservableSource<String>>() {
        @Override
        public ObservableSource<String> apply(@NonNull List<String> ids) throws Exception {
            return Observable.fromIterable(ids);
        }
    }).zipWith(RxView.clicks(v).debounce(500, TimeUnit.MILLISECONDS), (n, i) -> n))    
    .flatMap(new Function<String, ObservableSource<Item>>() {
        @Override
        public ObservableSource<Item> apply(@NonNull final String id) throws Exception {
            return dataApi.get(id).map(new Function<Data, Item>() {
                @Override
                public Item apply(@NonNull Data data) throws Exception {
                    return new Item(data , id);
            });
        }
    });
}

to get N items with each click

public Observable<Item> getN(View v, int nitems) {
    return idApi.get().flatMap(new Function<List<String>, ObservableSource<String>>() {
            @Override
            public ObservableSource<String> apply(@NonNull List<String> ids) throws Exception {
                return Observable.fromIterable(ids);
            }
        }).buffer(nitems).zipWith(RxView.clicks(v).debounce(500, TimeUnit.MILLISECONDS), (n, i) -> n))
        .flatMap(new Function<List<String>, ObservableSource<String>>() {
            @Override
            public ObservableSource<String> apply(@NonNull final List<String> ids) throws Exception {
                return Observable.from(ids)
            }
         }
        )  
        .flatMap(new Function<String, ObservableSource<Item>>() {
            @Override
            public ObservableSource<Item> apply(@NonNull final String id) throws Exception {
                return dataApi.get(id).map(new Function<Data, Item>() {
                    @Override
                    public Item apply(@NonNull Data data) throws Exception {
                        return new Item(data , id);
                 });
               }
         }
        });
 }

Edit: You will still have to use subscribeOn to make sure you are on the main thread for RXView.clicks and on the IO thread for any networking.

Answer 2

Not so good but it works:

your get method:

Observable<Item> get(final String id){
    return Observable.defer(() -> {
    dataApi.get(id).map(new Function<Data, Item>() {
            @Override
            public Item apply(@NonNull Data data) throws Exception {
                return new Item(data , id);
        });
    })
}

your click:

private List<String> ids = {//your id s}
private int current = 0;

RxView.clicks(view).flatmap(ignore -> get(ids.get(current++)))
                   .subscribe(//your Observer)

I'd like recommend that answer with zipwith(), seems better than my answer.