RxJava in practice

Slides for a workshop about RxJava & RxAndroid delivered at the Codemotion 2015.

Transcript

1. MADRID · NOV 27-28 · 2015 RxJava in practice Javier Gamarra
2. MADRID · NOV 27-28 · 2015 http://kcy.me/29crj (slides) & http://kcy.me/296bu (commits)
3. MADRID · NOV 27-28 · 2015 Environment Eclipse | Android Studio (RxAndroid) RxJava.jar [Java 8] || [Retrolambda] :P
4. 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
5. MADRID · NOV 27-28 · 2015 Github • http://kcy.me/296bu • koans • código • commit a commit • Podéis preguntarme en cualquier momento
6. MADRID · NOV 27-28 · 2015 Who? Javier Gamarra / @nhpatt @liferay @cyliconvalley / @agilespain
7. MADRID · NOV 27-28 · 2015 Ask! Please? Pretty please? Please pretty please with sugar on top?
8. MADRID · NOV 27-28 · 2015 Background?
9. MADRID · NOV 27-28 · 2015 Why?
10. MADRID · NOV 27-28 · 2015 Why? (in java) multithreading is hard futures are complicated callbacks are hell
11. MADRID · NOV 27-28 · 2015 Rx comes to the rescue!
12. 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
13. MADRID · NOV 27-28 · 2015 a library
14. MADRID · NOV 27-28 · 2015 A library? Extensions to .NET framework Netflix
15. MADRID · NOV 27-28 · 2015 Libraries are tools If all you have is a hammer, everything looks like a nail
16. MADRID · NOV 27-28 · 2015 a library to model Observables & Subscribers
17. MADRID · NOV 27-28 · 2015 Observables and Subscribers An Observable emits items. A Subscriber consumes those items.
18. MADRID · NOV 27-28 · 2015 Observer pattern?
19. MADRID · NOV 27-28 · 2015 My very first observable Observable<String> myObs = Observable. create(new Observable. OnSubscribe<String>() { @Override public void call(Subscriber<? super String> subscriber) { subscriber.onNext( "Hi!"); subscriber.onCompleted(); } });
20. MADRID · NOV 27-28 · 2015 My very first subscriber Subscriber<String> mySubs = new Subscriber<String>() { @Override public void onCompleted() { } @Override public void onError(Throwable throwable) { } @Override public void onNext(String s) { System. out.println(s); } };
21. MADRID · NOV 27-28 · 2015 My very first subscription myObs.subscribe(mySubs);
22. MADRID · NOV 27-28 · 2015 A bit verbose... Let’s simplify with Java8 and RxJava • lamdbas • Observable.just • .subscribe()
23. MADRID · NOV 27-28 · 2015 That’s better... Observable .just("Hi!") .subscribe(System.out::println);
24. MADRID · NOV 27-28 · 2015 Why? More than the observer pattern • Observables only emit when someone listening • OnFinished • OnError
25. MADRID · NOV 27-28 · 2015 Let’s use those differences subscribe admits 3 parameters • OnNext • OnFinished • OnError
26. MADRID · NOV 27-28 · 2015 You said “items” Observable.from admits a list of elements
27. MADRID · NOV 27-28 · 2015 Ok, let’s recap… Iterators?
28. MADRID · NOV 27-28 · 2015 Iterators? • Iterators are pull and synchronous • Subscribers are push and asynchronous
29. MADRID · NOV 27-28 · 2015 to represent any operation as an “asynchronous data stream”
30. MADRID · NOV 27-28 · 2015 Everything is a stream
31. MADRID · NOV 27-28 · 2015 Everything is a stream We can model everything as a stream
32. MADRID · NOV 27-28 · 2015 Everything is a stream A network call is also a stream Like using retrofit with this API
33. MADRID · NOV 27-28 · 2015 “declaratively composed”
34. MADRID · NOV 27-28 · 2015 Operators
35. MADRID · NOV 27-28 · 2015 Operators Transform a stream rxmarbles and android app
36. MADRID · NOV 27-28 · 2015 Operators Map
37. MADRID · NOV 27-28 · 2015 Map List<String> severalThings = Arrays.asList("1", "2"); Observable.from(severalThings) .map((s) -> “Element “ + s) .subscribe(System.out::println);
38. MADRID · NOV 27-28 · 2015 Map We can return another type: List<String> severalThings = Arrays.asList("1", "2"); Observable.from(severalThings) .map(Integer::valueOf) .subscribe(System.out::println);
39. 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
40. MADRID · NOV 27-28 · 2015 Flatmap Flatmap Obs -> elements
41. MADRID · NOV 27-28 · 2015 Flatmap service.listRepos("nhpatt") .flatMap(Observable::from) .map(Repo::getName) .map((s) -> s.replace("-", " ")) .subscribe(System.out::println);
42. MADRID · NOV 27-28 · 2015 Flatmap Concatmap -> ordered flatmap
43. 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);
44. 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);
45. 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;
46. MADRID · NOV 27-28 · 2015 Operators • merge • flatMap • zip Nice things™ : parallel jobs!
47. MADRID · NOV 27-28 · 2015 Zipping requests Observable<Repo> repo = service.listRepos("nhpatt") .flatMap(Observable::from) .take(1); Observable<Commit> commit = service.listCommits("nhpatt", "Android") .flatMap(Observable::from) .take(1); Observable.zip(repo, commit, this::updateCommit).subscribe (repo1 -> { System.out.println(repo1.getCommit().getUrl()); });
48. MADRID · NOV 27-28 · 2015 Operators Amazing documentation • Async • Blocking • Combining • Conditional • Error handling • Filtering • Mathematical • Creation • String • Transforming • Utility
49. MADRID · NOV 27-28 · 2015 Subscribers are asynchronous? No, not really
50. MADRID · NOV 27-28 · 2015 “on any thread”
51. MADRID · NOV 27-28 · 2015 Schedulers!
52. 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 ...
53. MADRID · NOV 27-28 · 2015 Schedulers .subscribeOn(Schedulers...) .observeOn(Schedulers...) • io • computation • newThread • trampoline • test
54. MADRID · NOV 27-28 · 2015 Schedulers service.listRepos("nhpatt") .subscribeOn(Schedulers.immediate()) .observeOn(Schedulers.immediate()) .subscribe(System.out::println);
55. MADRID · NOV 27-28 · 2015 Schedulers RxJava operators have default threads Interval?
56. MADRID · NOV 27-28 · 2015 Use cases?
57. 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
58. MADRID · NOV 27-28 · 2015 Android?
59. MADRID · NOV 27-28 · 2015 Why?
60. 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
61. MADRID · NOV 27-28 · 2015 How RxAndroid helps?
62. MADRID · NOV 27-28 · 2015 Android schedulers service.listRepos("nhpatt") .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(newRepos -> { repos.addAll(newRepos); adapter.notifyDataSetChanged(); });
63. MADRID · NOV 27-28 · 2015 Orientation Problem Orientation Problem • onCreate gets called again • state is lost
64. MADRID · NOV 27-28 · 2015 Orientation Problem Programmer’s job: • Store/Restore state • Restore view • Call again the user task? • Wait until it finishes?
65. MADRID · NOV 27-28 · 2015 How RxAndroid helps?
66. MADRID · NOV 27-28 · 2015 Orientation Problem Observable is easy to persist (retain | singleton) Observable can continue (cache and retry) RxLifecycle
67. MADRID · NOV 27-28 · 2015 Orientation Problem Observable<List<Repo>> github = RetrofitService. getGithub() .listRepos("nhpatt") .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .cache();
68. MADRID · NOV 27-28 · 2015 More Android Lifecycle (RxLifecyle) Views (RxBinding)
69. MADRID · NOV 27-28 · 2015 But...
70. 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
71. MADRID · NOV 27-28 · 2015 Easy to unsubscribe @Override protected void onStop() { super.onStop(); subscription.unsubscribe(); } .isUnsubscribed() :(
72. MADRID · NOV 27-28 · 2015 Let’s recap
73. 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
74. MADRID · NOV 27-28 · 2015 a library to represent any operation as an observable on any thread, declaratively composed, and consumed by multiple objects
75. MADRID · NOV 27-28 · 2015 a library to represent any operation as an observable with schedulers declaratively composed, and consumed by multiple objects
76. MADRID · NOV 27-28 · 2015 a library to represent any operation as an observable with schedulers and operators and consumed by multiple objects
77. MADRID · NOV 27-28 · 2015 a library to represent any operation as an observable with schedulers and operators listened by subscribers
78. MADRID · NOV 27-28 · 2015 But...
79. MADRID · NOV 27-28 · 2015 But... • Learning curve • Hard to debug (Frodo library) • Backpressure
80. MADRID · NOV 27-28 · 2015 Questions?
81. MADRID · NOV 27-28 · 2015 Where to know more... • reactivex.io (amazing docs) • RxJava wiki • Dan Lew • Use cases
82. MADRID · NOV 27-28 · 2015 Where to know more... nhpatt (twitter | github | email | slack) I’ll do anything for good votes
83. MADRID · NOV 27-28 · 2015 Feedback Click here :P
84. MADRID · NOV 27-28 · 2015 RxJava in practice Javier Gamarra
85. MADRID · NOV 27-28 · 2015 Other interesting operators...
86. 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);
87. MADRID · NOV 27-28 · 2015 Operators distinctUntilChanged compose
88. MADRID · NOV 27-28 · 2015 Errors?
89. 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
90. MADRID · NOV 27-28 · 2015 Errors And we can customize the flow: onErrorResumeNext onErrorReturn retry ...
91. MADRID · NOV 27-28 · 2015 Why this is useful?
92. MADRID · NOV 27-28 · 2015 Why this is useful? Observables and subscribers can do anything
93. MADRID · NOV 27-28 · 2015 Why this is useful? Observable a database query Subscriber displaying results on the screen
94. MADRID · NOV 27-28 · 2015 Why this is useful? Observable a click on the screen Subscriber reacting to it
95. MADRID · NOV 27-28 · 2015 Why this is useful? Observable a stream of bytes from the internet Subscriber write them to disk
96. MADRID · NOV 27-28 · 2015 Why this is useful? Observable and Subscriber are independent of the transformations
97. MADRID · NOV 27-28 · 2015 Why this is useful? I can compose/chain any map/filter calls I want Only matters the return type
98. MADRID · NOV 27-28 · 2015 Side effects?
99. MADRID · NOV 27-28 · 2015 Side effects doOn methods: • doOnNext() for debugging • doOnError() for error handling • doOnNext() to save/cache results
100. 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) );
101. MADRID · NOV 27-28 · 2015 Side effects flatMap(id -> service.get() .doOnError(t -> { // report problem to UI }) .onErrorResumeNext(Observable.empty()))
102. MADRID · NOV 27-28 · 2015 Cold & Hot
103. MADRID · NOV 27-28 · 2015 Cold & Hot Observables only emit when someone listening? Cold observables only emit when subscribed But hot observables emit instantly
104. 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()
105. MADRID · NOV 27-28 · 2015 Cold & Hot publish & connect? “like transactions” Assume everything is cold
106. MADRID · NOV 27-28 · 2015 Testing?
107. MADRID · NOV 27-28 · 2015 More cool things? • testscheduler • toIterator() • Obs.error(), Obs.empty()
108. MADRID · NOV 27-28 · 2015 Subjects
109. MADRID · NOV 27-28 · 2015 Subjects Both observable & observer
110. MADRID · NOV 27-28 · 2015 Subjects AsyncSubject -> takeLast(1) PublishSubject -> publish() ReplaySubject -> replay()/cache() BehaviorSubject -> replay(1)/cache(1)
111. MADRID · NOV 27-28 · 2015 RxJava in practice Javier Gamarra