Handling lists with RxJava and Retrofit in android

Question

I have couple of api calls to make (sequentially, asynchronously) and some of them returns lists. My api interface is given below.

@GET("/users/settings")
Observable<UserWrapper> getUserSettings();

@GET("/{username}/collections")
Observable<List<Item>> getItems(@Path("username") String userName);

@GET("/item/{id}")
Observable<ItemInfo> getItemInfo(@Path("id") int id);

@GET("/{username}/friends")
Observable<List<Friend>> getFriends(@Path("username") String userName);

Here's what I want to do sequentially:

Get UserWrapper by calling getUserSettings()
Save the user by calling saveUser(userWrapper)
Get user's items by calling getItems(userWrapper.getUserName())
Get each item's information by calling getItemInfo(item.getId())
Save each itemInfo by calling saveItem(itemInfo)
Get user's friends by calling getFriends(userWrapper.getUserName())
Save each friend by calling saveFriend(friend)

Now I am new to RxJava and do not know how to handle lists. I watched one of Jake Wharton's slides and found that he uses a function flattenList() but I don't know its definition. It would be great if you can help composing this chain.

Update 1

This is as far I've gotten now:

mApiService.getUserSettings()
            .map(this::saveUser)
            .flatMap(userWrapper -> mApiService.getItems(userWrapper.getUserName()));
            .flatMapIterable( ? "How to iterate for each item" ? );

Update 2

I am trying to write something like this

mApiService.getUserSettings()
    .map(this::saveUser)
    .flatMap(userWrapper -> mApiService.getItems(userWrapper.getUserName()))
    .someMethodToIterateThroughEachItem(item -> mApiService.getItemInfo(item))
    .map(this::saveItem)
    .someMethodThatCanCallUserWrapperAgain(userWrapper -> mApiService.getFriends(userWrapper.getUserName()))
    .someMethodToIterateThoughEachFriend(friend -> saveFriend(friend))

What is someMethodToIterateThroughEachItem? How does that compile? — IgorGanapolsky
– IgorGanapolsky, Commented Oct 5, 2015 at 15:35
Please give more details about someMethodToIterateThroughEachItem, someMethodThatCanCallUserWrapperAgain, and someMethodToIterateThoughEachFriend — Nguyen Minh Binh
– Nguyen Minh Binh, Commented Dec 9, 2015 at 6:22

zsxwing · Accepted Answer · 2014-12-30 11:29:19Z

20

RxJava has added flatMapIterable. So you don't need flattenList now. E.g.,

  Observable<UserWrapper> o =
       getUserSettings()
       .doOnNext(this::saveUser)
       .flatMap(user -> getItems(user.getUserName())
                        .flatMapIterable(items -> items)
                        .flatMap(item -> getItemInfo(item.getId()))
                        .doOnNext(this::saveItem)
                        .toList()
                        .map(ignored -> user))
        .flatMap(user -> getFriends(user.getUserName())
                         .flatMapIterable(friends -> friends)
                         .doOnNext(this::saveFriend)
                         .toList()
                         .map(ignored -> user)
        );
    o.subscribe(...);

edited Dec 30, 2014 at 11:29

answered Dec 30, 2014 at 4:17

zsxwing

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3 Comments

Raquib-ul Alam Over a year ago

Thanks @zsxwing, I have gotten to this point already. Please check my updated question How do I iterate through each item in this call. Isn't there any built in function in RxJava already?

zsxwing Over a year ago

Could you elaborate what you want to do?

Raquib-ul Alam Over a year ago

I've updated the question again for your better understanding. Please read bullet points too. Hope this answers your question.

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