我使用firebase来实时获取对象，我想按顺序（先进先出）执行更多的观察，谢谢！

public void getDispatch(Dispatch dispatch) {
    Single<DispatchAction> observable =  Single.just(dispatch)
    .map(order1 -> {
        return convertDispatch(order1);
    });

   DisposableSingleObserver<DispatchAction> actionDisposableObserver =
             new DisposableSingleObserver<DispatchAction>(){
        @Override
        public void onSuccess(DispatchAction action) {//Process result }

        public void onError(Throwable e) {//Error }
   };

   compositeDisposable.add(
        observable
        .subscribeOn(Schedulers.single())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribeWith(actionDisposableObserver)
   );
}