[英]RxJava- Consolidating multiple, infinite Observable<List<T>>?
這是我正在處理的一個有趣的 RxJava 小謎題。 假設我有一個Observable<List<Parent>> infiniteParentListStream
是無限的,每個Parent
都有一個Observable<List<Child>> infiniteChildListStream
屬性,它也是無限的。
我想獲取發出的List<Parent>
中的所有Parent
實例,並將它們發出的每個List<Child>
項目合並為一個完整的List<Child>
反映所有父項的所有子項。
事實上, Parent
的Observable<List<Child>> infiniteChildListStream
屬性是無限的,這使得toList()
任務有點挑戰。
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 {
}
}
當然,我找到的一種解決方法是通過調用first()
來將infiniteChildListStream
變為有限。 但這並不理想,因為它不再更新。
Observable<List<Child>> allCurrentChildren = infiniteParentListStream.<List<Child>>flatMap(parentList ->
Observable.from(parentList)
.flatMap(p -> p.getInfiniteChildListStream().first().flatMap(Observable::from)).toList()
).cache(1);
我覺得有一種方法可以手動調用Observable.create()
或使用flatMap()
技巧來解決這個問題。 有沒有更好的方法來做到這一點並使事物與無限源保持反應? 在我這個 SSCCE 之外的實際應用程序中,這些 observables 是無限的,因為驅動Parent
和Child
的數據源可能會改變並發出新的值......
我想我的問題的根源是如何獲取多個無限Observable<List<T>>
並將它們合並為一個Observable<List<T>>
?
我想我是通過使用Observable.combineLatest()
弄清楚的。 為了增強測試,我還修改了源 observables 以根據主題的推送整數值創建不同的List
大小。 這看起來很漂亮。
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 {
}
}
輸出:
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:創建了一個變壓器來執行這個任務
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;
}))
);
}
}
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