Rxjava flatMap concatMap

flatMap 一般用于输出一个 Observable，而其随后的 subscribe 中的参数也跟 Observable 中的参数一样。
下面再提供一个使用场景，这个场景属于嵌套的网络请求，比如我们想先进行一次网络请求得到图片的url，然后根据url再进行网络请求得到图片，最后设置给 ImageView ，这种情况下由url到 Bitmap 的转换用 map 是无法实现的，可以使用 flatmap。

Observable.create(new ObservableOnSubscribe() {
    @Override
    public void subscribe(@NonNull ObservableEmitter observableEmitter) throws Exception {
        String url = getImageUrl(mUrl);
        observableEmitter.onNext(url);
        observableEmitter.onComplete();
    }
      }).subscribeOn(Schedulers.io())
        .observeOn(Schedulers.io())
        .flatMap(new Function>() {
            @Override
            public ObservableSource apply(@NonNull final String url) throws Exception {
                return Observable.create(new ObservableOnSubscribe() {
                    @Override
                    public void subscribe(@NonNull ObservableEmitter observableEmitter) throws Exception {
                        Bitmap bitmap = getBitmap(url);
                        observableEmitter.onNext(bitmap);
                        observableEmitter.onComplete();
                    }
                });
            }
        })
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(new Consumer() {
            @Override
            public void accept(Bitmap bitmap) throws Exception {
                mImageView.setImageBitmap(bitmap);
            }
        });

更多flatmap 案例

   private void initData() {


        Flowable.fromIterable(getAllStudentInfoById())
                .flatMap(new Function>() {
                    @Override
                    public Publisher apply(@NonNull Student student) throws Exception {
                        return Flowable.fromIterable(student.mSources);
                    }
                })
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer() {
                    @Override
                    public void accept(@NonNull Source source) throws Exception {
                        String content = "sourceName:" + source.name + " source score:" + source.score;
//                        mTextView.setText(content);
                        Log.i(TAG, content);

                    }
                });
    }

    public List getAllStudentInfoById() {
        List studentList = new ArrayList<>();
        for (int i = 0; i < 3; i++) {

            List sources = new ArrayList<>();

            for (int j = 0; j < 3; j++) {
                Random random = new Random();
                int score = random.nextInt(100);
                Source source = new Source(j, "科目-" + j, score);
                sources.add(source);
            }

            Student student = new Student("xxx-" + i, i, sources);

            studentList.add(student);

        }

        return studentList;
    }

concatMap操作符的功能和flatMap是非常相似的，只是有一点，concatMap 最终输出的数据序列和原数据序列是一致，它是按顺序链接Observables，而不是合并(flatMap用的是合并)。

// concatmap

 Observable.fromArray(1,2,3,4,5)
                .concatMap(new Function>() {
                    @Override
                    public ObservableSource apply(@NonNull Integer integer) throws Exception {

                        int delay = 0;
                        if(integer == 3){
                            delay = 500;//延迟500ms发射
                        }
                        return Observable.just(integer *10).delay(delay, TimeUnit.MILLISECONDS);
                    }
                })
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer() {
                    @Override
                    public void accept(@NonNull Integer integer) throws Exception {
                        Log.e(TAG,"accept:"+integer);
                    }
                });

打印结果为

image.png

// flatmap
  Observable.fromArray(1,2,3,4,5)
                .flatMap(new Function>() {
                    @Override
                    public ObservableSource apply(@NonNull Integer integer) throws Exception {

                        int delay = 0;
                        if(integer == 3){
                            delay = 500;//延迟500ms发射
                        }
                        return Observable.just(integer *10).delay(delay, TimeUnit.MILLISECONDS);
                    }
                })
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer() {
                    @Override
                    public void accept(@NonNull Integer integer) throws Exception {
                        Log.e(TAG,"accept:"+integer);
                    }
                });

打印结果

image.png