RxJava 2.x 之聚合操作符

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聚合操作符

• startWith操作符
• startWithArray操作符
• concat/concatArray操作符
• merge/mergeArray操作符
• concatDelayError/mergeDelayError操作符
• zip操作符
• combineLatest操作符
• combineLatestDelayError操作符
• reduce操作符
• count操作符
• collect操作符

startWith

startWith操作符主要用来在发送元素之前追加数据

Observable.just(1, 2, 3, 4, 5)
          .startWith(Observable.just(7, 8, 9))
          .subscribeWith(new CommonObserver<>());

输出:

onNext 7
onNext 8
onNext 9
onNext 1
onNext 2
onNext 3
onNext 4
onNext 5
onComplete

Process finished with exit code 0

startWithArray

startWithArray操作符主要用来发送元素之前追加多个元素

Observable.just(1, 2, 3, 4, 5)
          .startWithArray(7, 8, 9)
          .subscribeWith(new CommonObserver<>());

输出:

onNext 7
onNext 8
onNext 9
onNext 1
onNext 2
onNext 3
onNext 4
onNext 5
onComplete

Process finished with exit code 0

concat/concatArray

concat和concatArray操作符串行执行

Observable.concat(
          Observable.just(1, 2),
          Observable.just(3, 4, 5),
          Observable.just(7, 8, 9))
          .subscribeWith(new CommonObserver<>());

输出:

onNext 1
onNext 2
onNext 3
onNext 4
onNext 5
onNext 7
onNext 8
onNext 9
onComplete

Process finished with exit code 0

注意: concat最多连接4个,而concatArray可以连接多个

merge/mergeArray

merge和mergeArray操作符主要用于合并多个被观察者并行执行

Observable.merge(
          Observable.intervalRange(0, 3, 1, 1, TimeUnit.SECONDS),
          Observable.intervalRange(3, 3, 1, 1, TimeUnit.SECONDS)
        ).subscribeWith(new CommonObserver<>());

输出:

onNext 0
onNext 3
onNext 1
onNext 4
onNext 2
onNext 5
onComplete

Process finished with exit code 0

注意: merge最多连接4个,而mergeArray可以连接多个

concatDelayError/mergeDelayError

使用concat和merge操作符时，如果遇到其中一个被观察者发出onError事件则会马上终止其他被观察者的事件，如果希望onError事件推迟到其他被观察者都结束后才触发，可以使用对应的concatDelayError或者mergeDelayError操作符

zip

zip操作符主要用来将多个观察者压缩成一个单独的操作

Observable.zip(
          Observable.just(1, 2),
          Observable.just(7, 9),
          (int1, int2) -> int1 + int2)
          .subscribeWith(new CommonObserver<>());

输出:

onNext 8
onNext 11
onComplete

Process finished with exit code 0

combineLatest

combineLatest操作符主要用于对同一个时间线上合并最后的元素

Observable.combineLatest(
          Observable.just(1, 2, 3),
          Observable.intervalRange(0, 5, 1, 1, TimeUnit.SECONDS),
          (int1, int2) -> int1 + int2)
          .subscribeWith(new CommonObserver<>());

输出:

onNext 3
onNext 4
onNext 5
onNext 6
onNext 7
onComplete

Process finished with exit code 0

combineLatestDelayError

combineLatestDelayError操作符主要处理delayError的问题

reduce

reduce操作符主要用来将所有元素聚合到一起

Observable.just(1, 2, 3)
          .reduce((last, item) -> {
          //先执行1+2，然后用1+2的结果和3相加，最后输出6，相当于把三个元素聚合在一起
          return last + item;
          })
          .subscribe(new CommonComsumer<>());

输出:

accept 6

Process finished with exit code 0

count

count操作符主要用来统计被观察者发送了多少个元素

Observable.just(1, 2, 3)
          .count()
          .subscribe(new CommonComsumer<>());

输出:

accept 3

Process finished with exit code 0

collect

collect和reduce操作符类似，不过它是需要自己定义收集的容器和收集逻辑

Observable.just(1, 2, 3)
          .collect(new Callable<ArrayList<Integer>>() {
                @Override
                public ArrayList<Integer> call() throws Exception {
                    return new ArrayList<>();
                }
          }, new BiConsumer<ArrayList<Integer>, Integer>() {
                @Override
                public void accept(ArrayList<Integer> list, Integer value) throws Exception {
                    System.out.println("add element " + value);
                    list.add(value);
                }
          })
          .subscribe(new CommonComsumer<>());

输出:

add element 1
add element 2
add element 3
accept [1, 2, 3]

Process finished with exit code 0

复习文档
https://github.com/byhook/rxjava2-study

参考：
https://maxwell-nc.github.io/android/rxjava2-4.html