android - RxJava的使用问题。

Question

更新叙述一下需求，其实就是简单的

取数据的时候先判断本地有无缓存，有缓存则从数据库中取得，否则从网络请求并且保存到本地。

因为才接触rxjava，这样写目前倒是完成了功能（运转正常），但是这样写真的是合理的吗？
本地数据库查询 queryDP
如果没查询到数据
deepSpaceBean=null
onNext（deepSpaceBean）

    @Override
    public Observable getDP(final String date) {
        return Observable
                .create(new Observable.OnSubscribe<DeepSpaceBean>() {
                    @Override
                    public void call(Subscriber<? super DeepSpaceBean> subscriber) {
                        DeepSpaceBean deepSpaceBean = null;
                        try {
                            deepSpaceBean = queryDP(date);
                        } catch (Exception e) {
                            e.printStackTrace();
                            XIAOHUException xiaohuException = new XIAOHUException(e, XIAOHUException.DB_QUERY);
                            subscriber.onError(xiaohuException);
                        }
                        subscriber.onNext(deepSpaceBean);
                        subscriber.onCompleted();
                    }
                });
    }"
    然后接下来的操作符

          .flatMap(new Func1<DeepSpaceBean, Observable<DeepSpaceBean>>() {
                @Override
                public Observable<DeepSpaceBean> call(DeepSpaceBean deepSpaceBean) {
                   **（关键1）** if (deepSpaceBean == null) {
                        return mDPsRemoteDataSource.getDP(date)
                                .doOnNext(new Action1<DeepSpaceBean>() {
                                    @Override
                                    public void call(DeepSpaceBean deepSpaceBean) {
                                        try {
                                            mDPsLoaclDataSource.saveDP(deepSpaceBean);
                                        } catch (Exception e) {
                                            e.printStackTrace();
                                        }
                                    }
                                });
                    } else {
                       **（关键2）** return Observable.just(deepSpaceBean);
                    }
                }
            });

关键1处，通过判断 发射源 的queryDP的返回值是否为空来区分执行不同的操作，
1为空 执行另一个mDPsRemoteDataSource.getDP(date)操作，retrofit的rx式返回

@Override
public Observable getDP(String date) {
    return PDORetrofit.getApiService().getAPOD(date);

}

    @GET("/planetary/apod?api_key=" + API_KEY)
Observable<DeepSpaceBean> getAPOD(@Query("date") String date);

 然后通过操作符doOnNext执行保存到本地数据库的操作（就是执行sql语句，返回为void，不关心结果）
关键处2，如果本地数据库查询（发射源）到了数据 deepSpaceBean != null，于是将它“包装”成observable重新发射出去。

Answer 1

I discovered that I can use the Concat operator to replace my bunch of confusing operations

Answer 2

rxJava is such an elegant class library that it nests so many mysteries for you, which makes you feel drunk

Answer 3

Since it can run normally, the explanation is reasonable. But the code structure and internal logic, if you write it like this, most people really can’t understand what you are writing!