一、scan语法

public Observable<Integer> getRxJavaCreateExampleData() {
        return Observable.create(new ObservableOnSubscribe<Integer>() {
            @Override
            public void subscribe(ObservableEmitter<Integer> emitter) throws Exception {
                LogUtils.debug(TAG, "getRxJavaCreateExampleData---:" + Thread.currentThread().getName() + "--:" + 1);
                emitter.onNext(1);

                LogUtils.debug(TAG, "getRxJavaCreateExampleData---:" + Thread.currentThread().getName() + "--:" + 2);
                emitter.onNext(2);
//                Thread.sleep(5000);
                LogUtils.debug(TAG, "getRxJavaCreateExampleData---:" + Thread.currentThread().getName() + "--:" + 3);
                emitter.onNext(3);
                emitter.onComplete();
                LogUtils.debug(TAG, "getRxJavaCreateExampleData---:" + Thread.currentThread().getName() + "--:" + 4);
                emitter.onNext(4);

            }
        });
    }
    public void rxJavaScanExample() {
        Disposable disposable = model.getRxJavaCreateExampleData()
                .subscribeOn(Schedulers.io())
                .unsubscribeOn(Schedulers.io())
                .scan( new BiFunction<Integer, Integer, Integer>() {
                    @Override
                    public Integer apply(Integer integer, Integer integer2) throws Exception {
                        LogUtils.error(TAG, "rxJavaScanExample--:" + Thread.currentThread().getName() + "-scan-:" + integer + "---" + integer2);
                        return integer+integer2;
                    }
                }).observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer<Integer>() {
                    @Override
                    public void accept(Integer integer) throws Exception {
                        LogUtils.error(TAG, "rxJavaReduceExample--:" + Thread.currentThread().getName() + "-consumer-:" + integer);
                    }
                });
        compositeDisposable.add(disposable);
    }

日志

08-19 15:16:15.864 12835-12880/com.example.zhang E/MainPresenter: rxJavaScanExample--:RxCachedThreadScheduler-1-scan-:1---2
08-19 15:16:15.865 12835-12880/com.example.zhang E/MainPresenter: rxJavaScanExample--:RxCachedThreadScheduler-1-scan-:3---3
08-19 15:16:15.867 12835-12835/com.example.zhang E/MainPresenter: rxJavaReduceExample--:main-consumer-:1
    rxJavaReduceExample--:main-consumer-:3
    rxJavaReduceExample--:main-consumer-:6

二、scan语法2

    public void rxJavaScanExample() {
        Disposable disposable = model.getRxJavaCreateExampleData()
                .subscribeOn(Schedulers.io())
                .unsubscribeOn(Schedulers.io())
                .scan(10, new BiFunction<Integer, Integer, Integer>() {
                    @Override
                    public Integer apply(Integer integer, Integer integer2) throws Exception {
                        LogUtils.error(TAG, "rxJavaScanExample--:" + Thread.currentThread().getName() + "-scan-:" + integer + "---" + integer2);
                        return integer+integer2;
                    }
                }).observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer<Integer>() {
                    @Override
                    public void accept(Integer integer) throws Exception {
                        LogUtils.error(TAG, "rxJavaReduceExample--:" + Thread.currentThread().getName() + "-consumer-:" + integer);
                    }
                });
        compositeDisposable.add(disposable);
    }

日志

08-19 15:14:12.876 12633-12692/com.example.zhang E/MainPresenter: rxJavaScanExample--:RxCachedThreadScheduler-1-scan-:10---1
08-19 15:14:12.877 12633-12692/com.example.zhang E/MainPresenter: rxJavaScanExample--:RxCachedThreadScheduler-1-scan-:11---2
    rxJavaScanExample--:RxCachedThreadScheduler-1-scan-:13---3
08-19 15:14:12.883 12633-12633/com.example.zhang E/MainPresenter: rxJavaReduceExample--:main-consumer-:10
    rxJavaReduceExample--:main-consumer-:11
    rxJavaReduceExample--:main-consumer-:13
    rxJavaReduceExample--:main-consumer-:16

总结

1、scan(BiFunction<T, T, T> accumulator) 把数据叠加起来
2、 scan(final R initialValue, BiFunction<R, ? super T, R> accumulator) initialValue给将叠加的数据添加一个初始值
3、scan与reduce的区别：reduce是只返回一次结果，scan是多次
4、scan返回次数等于初始值一次+emitter发送数据size ，如果没有初始值，则emitter发送数据的第一个当初始值

河马过河微信公众号.jpg