Question

这是我正在处理的一个有趣的小RxJava拼图。我们假设我的Observable<List<Parent>> infiniteParentListStream是无限的，每个Parent都有一个Observable<List<Child>> infiniteChildListStream属性也是无限的。

我想在发出的Parent中获取所有List<Parent>个实例，并将每个发出的List<Child>个项合并为一个整体List<Child>，反映所有子项父母。

Observable<List<Child>> infiniteChildListStream中Parent属性无限的事实使toList()任务变得有点挑战。

public final class NestedInfiniteTest {

    private static final BehaviorSubject<Integer> parentSubject = BehaviorSubject.create(1);
    private static final BehaviorSubject<Integer> childSubject = BehaviorSubject.create(1);

    public static void main(String[] args) {


        Observable<List<Parent>> infiniteParentListStream = parentSubject
                .map(i -> Arrays.asList(new Parent(), new Parent(), new Parent()))
                .cache(1);

        Observable<List<Child>> allCurrentChildren = infiniteParentListStream.<List<Child>>flatMap(parentList ->
                Observable.from(parentList)
                        .flatMap(p -> p.getInfiniteChildListStream().flatMap(Observable::from)).toList()
        ).cache(1);

        allCurrentChildren.subscribe(cl -> System.out.println("WHOLE CHILD LIST SIZE: " + cl.size()));
    }

    private static final class Parent {
        private final Observable<List<Child>> infiniteChildListStream = childSubject
                .map(i -> Arrays.asList(new Child(), new Child(), new Child())).cache(1);

        public Observable<List<Child>> getInfiniteChildListStream() {
            return infiniteChildListStream;
        }
    }
    private static final class Child {

    }
}

我找到的一种解决方法当然是通过调用infiniteChildListStream来改变first()。但这不太理想，因为它不再更新。

Observable<List<Child>> allCurrentChildren = infiniteParentListStream.<List<Child>>flatMap(parentList ->
        Observable.from(parentList)
                .flatMap(p -> p.getInfiniteChildListStream().first().flatMap(Observable::from)).toList()
).cache(1);

我觉得有一种方法可以手动调用Observable.create()或使用flatMap()技巧来解决此问题。有没有更好的方法来做到这一点，并保持与无限来源的反应？在我在SSCCE之外的实际应用中，这些可观察量是无限的，因为驱动Parent和Child的数据源可能会改变并发出新值......

我想我的问题的根源是如何获取多个无限Observable<List<T>>并将它们合并为一个Observable<List<T>>？

Answer 1

我想我是通过使用Observable.combineLatest()来解决的。为了增强测试，我还修改了源可观察量，以根据主题推送的整数值创建不同的List大小。这看起来很漂亮。

public final class NestedInfiniteTest {

    private static final BehaviorSubject<Integer> parentSubject = BehaviorSubject.create(1);
    private static final BehaviorSubject<Integer> childSubject = BehaviorSubject.create(1);

    public static void main(String[] args) {

        Observable<List<Parent>> infiniteParentListStream = parentSubject
                .map(i -> IntStream.range(0,i).mapToObj(val -> new Parent()).collect(Collectors.toList()))
                .cache(1);

        Observable<List<Child>> allCurrentChildren = infiniteParentListStream.flatMap(parentList ->
                Observable.<Observable<List<Child>>>create(s -> {
                    parentList.stream().map(Parent::getInfiniteChildListStream).forEach(s::onNext);
                    s.onCompleted();
                })
                .toList() //List<<Observable<List<Child>>>>
                .flatMap(consolidatedChildList -> Observable.combineLatest(consolidatedChildList, new FuncN<List<Child>>() {
                    @Override
                    public List<Child> call(Object... args) {
                        ArrayList<Child> list = new ArrayList<>();
                        for (Object obj : args) {
                            list.addAll((List<Child>) obj);
                        }
                        return list;
                    }
                }))
        );


        allCurrentChildren.subscribe(cl -> System.out.println("WHOLE CHILD LIST SIZE: " + cl.size()));
        childSubject.onNext(10);
        parentSubject.onNext(5);
        childSubject.onNext(2);
    }

    private static final class Parent {
        private final Observable<List<Child>> infiniteChildListStream = childSubject
                .map(i -> IntStream.range(0, i).mapToObj(val -> new Child()).collect(Collectors.toList())).cache(1);

        public Observable<List<Child>> getInfiniteChildListStream() {
            return infiniteChildListStream;
        }
    }
    private static final class Child {

    }
}

输出：

WHOLE CHILD LIST SIZE: 1   //parentSubject = 1, childSubject = 1
WHOLE CHILD LIST SIZE: 10  //parentSubject = 1, childSubject = 10
WHOLE CHILD LIST SIZE: 50  //parentSubject = 5, childSubject = 10
WHOLE CHILD LIST SIZE: 2   //parentSubject = 5, childSubject = 2, adjusting
WHOLE CHILD LIST SIZE: 42  //adjusting
WHOLE CHILD LIST SIZE: 34  //adjusting
WHOLE CHILD LIST SIZE: 26  //adjusting
WHOLE CHILD LIST SIZE: 18  //adjusting
WHOLE CHILD LIST SIZE: 10  //parentSubject = 5, childSubject = 2, done!

更新：创建了一个Transformer来执行此任务

public static class CombinedListTransformer<T,R> implements Observable.Transformer<List<T>,List<R>> {

    private final Func1<T,Observable<List<R>>> listMapper;

    public CombinedListTransformer(Func1<T,Observable<List<R>>> listMapper) {
        this.listMapper = listMapper;
    }
    @Override
    public Observable<List<R>> call(Observable<List<T>> sourceList) {
        return sourceList.flatMap(sl ->
            Observable.from(sl).map(t -> listMapper.call(t)).toList() //List<Observable<List<R>>
            .flatMap(consolidatedChildList -> Observable.combineLatest(consolidatedChildList, args -> {
                ArrayList<R> list = new ArrayList<>();
                for (Object obj : args) {
                    list.addAll((List<R>) obj);
                }
                return list;
            }))
        );
    }
}

RxJava-整合多个无限的Observable <list <t>＆gt;？

1 个答案: