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MADRID · NOV 27-28 · 2015 RxJava in practice Javier Gamarra

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MADRID · NOV 27-28 · 2015 http://kcy.me/29crj (slides) & http://kcy.me/296bu (commits)

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MADRID · NOV 27-28 · 2015 Environment Eclipse | Android Studio (RxAndroid) RxJava.jar [Java 8] || [Retrolambda] :P

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MADRID · NOV 27-28 · 2015 Environment Android Studio: compile 'io.reactivex:rxandroid:1.0.1' compile 'io.reactivex:rxjava:1.0.16' Eclipse: ● Copy jars to lib/ and add jar in project

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MADRID · NOV 27-28 · 2015 Github ● http://kcy.me/296bu ● koans ● código ● commit a commit ● Podéis preguntarme en cualquier momento

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MADRID · NOV 27-28 · 2015 Who? Javier Gamarra / @nhpatt @liferay @cyliconvalley / @agilespain

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MADRID · NOV 27-28 · 2015 Ask! Please? Pretty please? Please pretty please with sugar on top?

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MADRID · NOV 27-28 · 2015 Background?

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MADRID · NOV 27-28 · 2015 Why?

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MADRID · NOV 27-28 · 2015 Why? (in java) multithreading is hard futures are complicated callbacks are hell

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MADRID · NOV 27-28 · 2015 Rx comes to the rescue!

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MADRID · NOV 27-28 · 2015 a library to represent any operation as an asynchronous data stream on any thread, declaratively composed, and consumed by multiple objects

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MADRID · NOV 27-28 · 2015 a library

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MADRID · NOV 27-28 · 2015 A library? Extensions to .NET framework Netflix

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MADRID · NOV 27-28 · 2015 Libraries are tools If all you have is a hammer, everything looks like a nail

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MADRID · NOV 27-28 · 2015 a library to model Observables & Subscribers

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MADRID · NOV 27-28 · 2015 Observables and Subscribers An Observable emits items. A Subscriber consumes those items.

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MADRID · NOV 27-28 · 2015 Observer pattern?

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MADRID · NOV 27-28 · 2015 My very first observable Observable myObs = Observable. create(new Observable. OnSubscribe() { @Override public void call(Subscriber subscriber) { subscriber.onNext( "Hi!"); subscriber.onCompleted(); } });

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MADRID · NOV 27-28 · 2015 My very first subscriber Subscriber mySubs = new Subscriber() { @Override public void onCompleted() { } @Override public void onError(Throwable throwable) { } @Override public void onNext(String s) { System. out.println(s); } };

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MADRID · NOV 27-28 · 2015 My very first subscription myObs.subscribe(mySubs);

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MADRID · NOV 27-28 · 2015 A bit verbose... Let’s simplify with Java8 and RxJava ● lamdbas ● Observable.just ● .subscribe()

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MADRID · NOV 27-28 · 2015 That’s better... Observable .just("Hi!") .subscribe(System.out::println);

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MADRID · NOV 27-28 · 2015 Why? More than the observer pattern ● Observables only emit when someone listening ● OnFinished ● OnError

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MADRID · NOV 27-28 · 2015 Let’s use those differences subscribe admits 3 parameters ● OnNext ● OnFinished ● OnError

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MADRID · NOV 27-28 · 2015 You said “items” Observable.from admits a list of elements

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MADRID · NOV 27-28 · 2015 Ok, let’s recap… Iterators?

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MADRID · NOV 27-28 · 2015 Iterators? ● Iterators are pull and synchronous ● Subscribers are push and asynchronous

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MADRID · NOV 27-28 · 2015 to represent any operation as an “asynchronous data stream”

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MADRID · NOV 27-28 · 2015 Everything is a stream

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MADRID · NOV 27-28 · 2015 Everything is a stream We can model everything as a stream

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MADRID · NOV 27-28 · 2015 Everything is a stream A network call is also a stream Like using retrofit with this API

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MADRID · NOV 27-28 · 2015 “declaratively composed”

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MADRID · NOV 27-28 · 2015 Operators

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MADRID · NOV 27-28 · 2015 Operators Transform a stream rxmarbles and android app

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MADRID · NOV 27-28 · 2015 Operators Map

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MADRID · NOV 27-28 · 2015 Map List severalThings = Arrays.asList("1", "2"); Observable.from(severalThings) .map((s) -> “Element “ + s) .subscribe(System.out::println);

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MADRID · NOV 27-28 · 2015 Map We can return another type: List severalThings = Arrays.asList("1", "2"); Observable.from(severalThings) .map(Integer::valueOf) .subscribe(System.out::println);

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MADRID · NOV 27-28 · 2015 Map Let’s do the same with our repos… And… I can’t because we return a List And using Observable.from… NOP

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MADRID · NOV 27-28 · 2015 Flatmap Flatmap Obs -> elements

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MADRID · NOV 27-28 · 2015 Flatmap service.listRepos("nhpatt") .flatMap(Observable::from) .map(Repo::getName) .map((s) -> s.replace("-", " ")) .subscribe(System.out::println);

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MADRID · NOV 27-28 · 2015 Flatmap Concatmap -> ordered flatmap

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MADRID · NOV 27-28 · 2015 Filter service.listRepos("nhpatt") .flatMap(Observable::from) .map(Repo::getName) .map((s) -> s.replace("-", " ")) .filter((s) -> s.startsWith("Android")) .subscribe(System.out::println);

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MADRID · NOV 27-28 · 2015 Scan & old code service.listRepos("nhpatt") .flatMap(Observable::from) .map(Repo::getName) .map((s) -> s.replace("-", " ")) .filter((s) -> s.startsWith("Android")) .take(2) .map(String::length) .scan((x, y) -> x * y) .subscribe(System.out::println);

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MADRID · NOV 27-28 · 2015 Scan & old code (l) -> { int result = 0; int i = 0; int oldLength = 1; for (Repo repo : l) { String name = repo.getName(); String replacedName = name.replace( "-", " "); if (replacedName.startsWith( "Android") && i < 2) { result = replacedName.length() * oldLength; oldLength = result; System.out.println(result); i++; } } return result;

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MADRID · NOV 27-28 · 2015 Operators ● merge ● flatMap ● zip Nice things™ : parallel jobs!

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MADRID · NOV 27-28 · 2015 Zipping requests Observable repo = service.listRepos("nhpatt") .flatMap(Observable::from) .take(1); Observable commit = service.listCommits("nhpatt", "Android") .flatMap(Observable::from) .take(1); Observable.zip(repo, commit, this::updateCommit).subscribe (repo1 -> { System.out.println(repo1.getCommit().getUrl()); });

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MADRID · NOV 27-28 · 2015 Operators Amazing documentation ● Async ● Blocking ● Combining ● Conditional ● Error handling ● Filtering ● Mathematical ● Creation ● String ● Transforming ● Utility

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MADRID · NOV 27-28 · 2015 Subscribers are asynchronous? No, not really

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MADRID · NOV 27-28 · 2015 “on any thread”

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MADRID · NOV 27-28 · 2015 Schedulers!

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MADRID · NOV 27-28 · 2015 Schedulers I define an API declaratively and later in the implementation run it: asynchronously or in a separate Thread or in a Threadpool or synchronously ...

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MADRID · NOV 27-28 · 2015 Schedulers .subscribeOn(Schedulers...) .observeOn(Schedulers...) ● io ● computation ● newThread ● trampoline ● test

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MADRID · NOV 27-28 · 2015 Schedulers service.listRepos("nhpatt") .subscribeOn(Schedulers.immediate()) .observeOn(Schedulers.immediate()) .subscribe(System.out::println);

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MADRID · NOV 27-28 · 2015 Schedulers RxJava operators have default threads Interval?

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MADRID · NOV 27-28 · 2015 Use cases?

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MADRID · NOV 27-28 · 2015 Use cases ● Autocomplete with debounce | sample… ● Accumulate calls with buffer... ● Polling with timeout | window… ● Form Validation with combineLatest… ● Retrieve data fast from cache | network call with concat | merge… ● Button click with delay, listen on other thread

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MADRID · NOV 27-28 · 2015 Android?

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MADRID · NOV 27-28 · 2015 Why?

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MADRID · NOV 27-28 · 2015 Why? (in android) Main/UI thread and background problem ● Can’t do heavy tasks on UI ● Can’t update view on background ● AsyncTasks are bad ● Handlers can leak

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MADRID · NOV 27-28 · 2015 How RxAndroid helps?

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MADRID · NOV 27-28 · 2015 Android schedulers service.listRepos("nhpatt") .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(newRepos -> { repos.addAll(newRepos); adapter.notifyDataSetChanged(); });

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MADRID · NOV 27-28 · 2015 Orientation Problem Orientation Problem ● onCreate gets called again ● state is lost

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MADRID · NOV 27-28 · 2015 Orientation Problem Programmer’s job: ● Store/Restore state ● Restore view ● Call again the user task? ● Wait until it finishes?

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MADRID · NOV 27-28 · 2015 How RxAndroid helps?

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MADRID · NOV 27-28 · 2015 Orientation Problem Observable is easy to persist (retain | singleton) Observable can continue (cache and retry) RxLifecycle

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MADRID · NOV 27-28 · 2015 Orientation Problem Observable> github = RetrofitService. getGithub() .listRepos("nhpatt") .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .cache();

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MADRID · NOV 27-28 · 2015 More Android Lifecycle (RxLifecyle) Views (RxBinding)

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MADRID · NOV 27-28 · 2015 But...

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MADRID · NOV 27-28 · 2015 But... Subscriptions leak memory :’( We have to call to unsubscribe (CompositeSubscription helps) And don’t include references to the object/activity

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MADRID · NOV 27-28 · 2015 Easy to unsubscribe @Override protected void onStop() { super.onStop(); subscription.unsubscribe(); } .isUnsubscribed() :(

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MADRID · NOV 27-28 · 2015 Let’s recap

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MADRID · NOV 27-28 · 2015 a library to represent any operation as an asynchronous data stream on any thread, declaratively composed, and consumed by multiple objects

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MADRID · NOV 27-28 · 2015 a library to represent any operation as an observable on any thread, declaratively composed, and consumed by multiple objects

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MADRID · NOV 27-28 · 2015 a library to represent any operation as an observable with schedulers declaratively composed, and consumed by multiple objects

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MADRID · NOV 27-28 · 2015 a library to represent any operation as an observable with schedulers and operators and consumed by multiple objects

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MADRID · NOV 27-28 · 2015 a library to represent any operation as an observable with schedulers and operators listened by subscribers

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MADRID · NOV 27-28 · 2015 But...

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MADRID · NOV 27-28 · 2015 But... ● Learning curve ● Hard to debug (Frodo library) ● Backpressure

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MADRID · NOV 27-28 · 2015 Questions?

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MADRID · NOV 27-28 · 2015 Where to know more... ● reactivex.io (amazing docs) ● RxJava wiki ● Dan Lew ● Use cases

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MADRID · NOV 27-28 · 2015 Where to know more... nhpatt (twitter | github | email | slack) I’ll do anything for good votes

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MADRID · NOV 27-28 · 2015 Feedback Click here :P

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MADRID · NOV 27-28 · 2015 RxJava in practice Javier Gamarra

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MADRID · NOV 27-28 · 2015 Other interesting operators...

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MADRID · NOV 27-28 · 2015 Take service.listRepos("nhpatt") .flatMap(Observable::from) .map(Repo::getName) .map((s) -> s.replace("-", " ")) .filter((s) -> s.startsWith("Android")) .take(2) .subscribe(System.out::println);

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MADRID · NOV 27-28 · 2015 Operators distinctUntilChanged compose

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MADRID · NOV 27-28 · 2015 Errors?

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MADRID · NOV 27-28 · 2015 onError() is called if an Exception is thrown at any time (this is cool) The operators don't have to handle the Exception No more callbacks Errors

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MADRID · NOV 27-28 · 2015 Errors And we can customize the flow: onErrorResumeNext onErrorReturn retry ...

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MADRID · NOV 27-28 · 2015 Why this is useful?

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MADRID · NOV 27-28 · 2015 Why this is useful? Observables and subscribers can do anything

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MADRID · NOV 27-28 · 2015 Why this is useful? Observable a database query Subscriber displaying results on the screen

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MADRID · NOV 27-28 · 2015 Why this is useful? Observable a click on the screen Subscriber reacting to it

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MADRID · NOV 27-28 · 2015 Why this is useful? Observable a stream of bytes from the internet Subscriber write them to disk

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MADRID · NOV 27-28 · 2015 Why this is useful? Observable and Subscriber are independent of the transformations

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MADRID · NOV 27-28 · 2015 Why this is useful? I can compose/chain any map/filter calls I want Only matters the return type

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MADRID · NOV 27-28 · 2015 Side effects?

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MADRID · NOV 27-28 · 2015 Side effects doOn methods: ● doOnNext() for debugging ● doOnError() for error handling ● doOnNext() to save/cache results

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MADRID · NOV 27-28 · 2015 Side effects Observable someObservable = Observable .from(Arrays.asList(new Integer[]{2, 7, 11})) .doOnNext(System.out::println) .filter(prime -> prime % 2 == 0) .doOnNext(System.out::println) .count() .doOnNext(System.out::println) .map( number -> String.format(“Contains %d elements”, number) );

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MADRID · NOV 27-28 · 2015 Side effects flatMap(id -> service.get() .doOnError(t -> { // report problem to UI }) .onErrorResumeNext(Observable.empty()))

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MADRID · NOV 27-28 · 2015 Cold & Hot

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MADRID · NOV 27-28 · 2015 Cold & Hot Observables only emit when someone listening? Cold observables only emit when subscribed But hot observables emit instantly

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MADRID · NOV 27-28 · 2015 Cold & Hot You can convert between both states ● “Hot -> cold” using defer() or merge(), zip()... ● “Cold -> Hot” using publish() & connect()

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MADRID · NOV 27-28 · 2015 Cold & Hot publish & connect? “like transactions” Assume everything is cold

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MADRID · NOV 27-28 · 2015 Testing?

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MADRID · NOV 27-28 · 2015 More cool things? ● testscheduler ● toIterator() ● Obs.error(), Obs.empty()

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MADRID · NOV 27-28 · 2015 Subjects

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MADRID · NOV 27-28 · 2015 Subjects Both observable & observer

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MADRID · NOV 27-28 · 2015 Subjects AsyncSubject -> takeLast(1) PublishSubject -> publish() ReplaySubject -> replay()/cache() BehaviorSubject -> replay(1)/cache(1)

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MADRID · NOV 27-28 · 2015 RxJava in practice Javier Gamarra