ReactiveX in Android

An introduction to RxJava and RxAndroid (v1) and Rx patterns

Transcript

1. RxAndroid Using ReactiveX in Android RxAndroid | Richard Cirerol | @codeprogression
2. Who am I? RxAndroid | Richard Cirerol | @codeprogression
3. Richard Cirerol @codeprogression http://codeprogression.com RxAndroid | Richard Cirerol | @codeprogression
4. Sr. Android Engineer at MLBAM RxAndroid | Richard Cirerol | @codeprogression
5. RxAndroid | Richard Cirerol | @codeprogression
6. http://bit.ly/mlbam-theverge RxAndroid | Richard Cirerol | @codeprogression
7. What is ReactiveX? - http://reactivex.io RxAndroid | Richard Cirerol | @codeprogression
8. The Observer pattern done right 4 Observer pattern 4 Iterator pattern 4 Functional programming 4 Asynchronous RxAndroid | Richard Cirerol | @codeprogression
9. Reactive extensions originated in .NET (circa 2010) RxAndroid | Richard Cirerol | @codeprogression
10. RxJava is a port of Rx.NET started by Netflix (circa 2013) RxAndroid | Richard Cirerol | @codeprogression
11. Languages - Java: RxJava - JavaScript: RxJS - C#: Rx.NET - C#(Unity): UniRx - Scala: RxScala - Clojure: RxClojure - C++: RxCpp - Ruby: Rx.rb - Python: RxPY - Groovy: RxGroovy - JRuby: RxJRuby - Kotlin: RxKotlin - Swift: RxSwift ReactiveX for platforms and frameworks - RxNetty - RxAndroid - RxCocoa RxAndroid | Richard Cirerol | @codeprogression
12. RxJava = Observables + Operators + Schedulers RxAndroid | Richard Cirerol | @codeprogression
13. RxAndroid = RxJava + Additional Schedulers RxAndroid | Richard Cirerol | @codeprogression
14. RxJava = Observables + Operators + Schedulers RxAndroid | Richard Cirerol | @codeprogression
15. Observable 4 Emits a stream of items to observers 4 Notifies observers of termination events 4 Error 4 Completed RxAndroid | Richard Cirerol | @codeprogression
16. Observable.just(0); RxAndroid | Richard Cirerol | @codeprogression
17. Observable.just(0); Observable.just(0, 1, 2); RxAndroid | Richard Cirerol | @codeprogression
18. // 5, 6, 7, 8, 9 Observable.range(5,5) RxAndroid | Richard Cirerol | @codeprogression
19. Integer[] items = new Integer[]{ 2, 4, 6, 8, 10 } Observable.from(items); RxAndroid | Richard Cirerol | @codeprogression
20. Observable.create(new OnSubscribe<Integer>() @Override public void call(Observer Observer){} try{ for (int i = 0; i < 5; i++){ observer.onNext(i); } observer.onCompleted() } catch(Exception e){ observer.onError(e); } } }); RxAndroid | Richard Cirerol | @codeprogression
21. ----------------------------> RxAndroid | Richard Cirerol | @codeprogression
22. ----1-----------------------> RxAndroid | Richard Cirerol | @codeprogression
23. ----1----20-----------------> RxAndroid | Richard Cirerol | @codeprogression
24. ----1----20---17------------> RxAndroid | Richard Cirerol | @codeprogression
25. ----1----20---17---8--------> RxAndroid | Richard Cirerol | @codeprogression
26. ----1----20---17---8----|---> RxAndroid | Richard Cirerol | @codeprogression
27. ----1----20---17---8----X---> RxAndroid | Richard Cirerol | @codeprogression
28. Observer 4 Subscribes to an Observable 4 Reacts to emitted items 4 Reacts to termination events RxAndroid | Richard Cirerol | @codeprogression
29. public interface Observer<T> { void onNext(T item); void onError(Throwable t); void onCompleted(); } RxAndroid | Richard Cirerol | @codeprogression
30. Single-threaded? Multi-threaded? RxAndroid | Richard Cirerol | @codeprogression
31. Synchronous? Asynchronous? RxAndroid | Richard Cirerol | @codeprogression
32. From a DB? A web service? A singleton? RxAndroid | Richard Cirerol | @codeprogression
33. Who cares? RxAndroid | Richard Cirerol | @codeprogression
34. Observer to Observable: Just tell me when you've got something new And tell me when you're done RxAndroid | Richard Cirerol | @codeprogression
35. Listener vs. Observable RxAndroid | Richard Cirerol | @codeprogression
36. Listener 4 Registration managed by the parent of the target 4 Callback interfaces are custom per implementation RxAndroid | Richard Cirerol | @codeprogression
37. // Before calling... service.getFoo(); // First call one of... service.setListener(this); service.addListener(this); // And implement... public interface Listener { void onFooChanged(Foo foo); } // And remember to clean up... service.setListener(null); service.removeListener(this); RxAndroid | Richard Cirerol | @codeprogression
38. Observables 4 Registration managed internally by the Observable 4 Subscription interface is consistent RxAndroid | Richard Cirerol | @codeprogression
39. // A Subscriber is a subclass of Observer Subscription subscription = service.getFoo() .subscribe(new Subscriber<Foo>(){ @Override public void onNext(Foo item){ doSomething(item); } @Override public void onError(Throwable e){ Log.e(e); } @Override public void onCompleted(){ hideProgress(); } }); RxAndroid | Richard Cirerol | @codeprogression
40. Subscription subscription = service.getFoo() .subscribe(new Action1<Foo>(){ @Override public void call(Foo foo){ doSomething(foo)); } }); RxAndroid | Richard Cirerol | @codeprogression
41. Subscription subscription = service.getFoo() .subscribe(new Action1<Foo>(){ @Override public void call(Foo foo){ doSomething(foo)); } }, new Action<Throwable>(){ @Override public void call(Throwable t){ Log.e(t); } }); RxAndroid | Richard Cirerol | @codeprogression
42. // Still need to cleanup subscription.unsubscribe(); RxAndroid | Richard Cirerol | @codeprogression
43. RxJava = Observables + Operators + Schedulers RxAndroid | Richard Cirerol | @codeprogression
44. Operators 4 Are a specialized observer 4 Can transform observables 4 Can be chained 4 A function that takes a Subscriber and returns a Subscriber RxAndroid | Richard Cirerol | @codeprogression
45. Observable.from({0, 1, 2, 3, 4}) .subscribe(); RxAndroid | Richard Cirerol | @codeprogression
46. Observable.from({0, 1, 2, 3, 4}) .skip(1) .map(new Func1<Integer, Integer>(){ @Override public Integer call(Integer in){ return in^2; } }) .subscribe(); RxAndroid | Richard Cirerol | @codeprogression
47. Observable.from({0, 1, 2, 3, 4}) .doOnNext(new Action1<Integer>(){ @Override public void call(Integer in){ return Log.i("Received: " + in); } }) .subscribe(); RxAndroid | Richard Cirerol | @codeprogression
48. Observable<Player> player; Observable<List<Team>> teams; Observable.combineLatest(player, teams, new Func2<Player, List<Team>, ViewModel>(){ @Override public ViewModel(Player player, List<Team> teams){ Team team = teams.get(player.getTeamId()); return new ViewModel(player.getName(), team.getName()); } }) .subscribe(...); RxAndroid | Richard Cirerol | @codeprogression
49. Observables are asynchronous by default A subscription will not block the thread when waiting for a value. RxAndroid | Richard Cirerol | @codeprogression
50. toBlocking() makes an Observable synchronous A subscription WILL block the thread when waiting for a value. RxAndroid | Richard Cirerol | @codeprogression
51. RxJava = Observables + Operators + Schedulers RxAndroid | Richard Cirerol | @codeprogression
52. Normally, operations are done on the current thread RxAndroid | Richard Cirerol | @codeprogression
53. Schedulers RxJava allows you to marshall operations to another thread. RxAndroid | Richard Cirerol | @codeprogression
54. Schedulers subscribeOn() and observeOn() are special operators RxAndroid | Richard Cirerol | @codeprogression
55. subscribeOn() declares the starting Scheduler RxAndroid | Richard Cirerol | @codeprogression
56. observeOn() declares the continuing Scheduler RxAndroid | Richard Cirerol | @codeprogression
57. RxJava Default Schedulers RxAndroid | Richard Cirerol | @codeprogression
58. Schedulers.immediate() RxAndroid | Richard Cirerol | @codeprogression
59. Schedulers.trampoline() RxAndroid | Richard Cirerol | @codeprogression
60. Schedulers.newThread() RxAndroid | Richard Cirerol | @codeprogression
61. Schedulers.computation() RxAndroid | Richard Cirerol | @codeprogression
62. Schedulers.io() RxAndroid | Richard Cirerol | @codeprogression
63. Schedulers.test() RxAndroid | Richard Cirerol | @codeprogression
64. Schedulers.from(Executor executor) RxAndroid | Richard Cirerol | @codeprogression
65. RxAndroid = RxJava + Additional Schedulers RxAndroid | Richard Cirerol | @codeprogression
66. AndroidSchedulers.mainThread() RxAndroid | Richard Cirerol | @codeprogression
67. HandlerScheduler.create(Looper looper) RxAndroid | Richard Cirerol | @codeprogression
68. Observable.create(s -> getFooFromWeb()) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(); RxAndroid | Richard Cirerol | @codeprogression
69. Observable.create(s -> getFooFromWeb()) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .map(foo -> calculateBar(foo)) // !! .subscribe(); RxAndroid | Richard Cirerol | @codeprogression
70. Observable.create(() -> getFooFromWeb()) .subscribeOn(Schedulers.io()) .observeOn(Schedulers.computation()) .map(foo -> calculateBar(foo)) .observeOn(AndroidSchedulers.mainThread()) .subscribe(); RxAndroid | Richard Cirerol | @codeprogression
71. Observable.create(s -> getFooFromWeb()) .subscribeOn(Schedulers.io()) .observeOn(Schedulers.computation()) .map(foo -> calculateBar(foo)) .observeOn(AndroidSchedulers.mainThread()) .subscribe(); RxAndroid | Richard Cirerol | @codeprogression
72. Let's break this up RxAndroid | Richard Cirerol | @codeprogression
73. // in publisher class public Observable<Bar> getBar(){ return Observable.create(s -> getFooFromWeb()) .subscribeOn(Schedulers.io()) .observeOn(Schedulers.computation()) .map(foo -> calculateBar(foo)) } // in subscriber class (presenter?) getBar() .observeOn(AndroidSchedulers.mainThread()); .subscribe(item -> updateView(item)); RxAndroid | Richard Cirerol | @codeprogression
74. private Bar cachedBar; public Observable<Bar> getBar(){ return Observable.create(s -> getFooFromWeb()) .subscribeOn(Schedulers.io()) .observeOn(Schedulers.computation()) .map(foo -> calculateBar(foo)) .doOnNext(bar -> cachedBar = bar) } RxAndroid | Richard Cirerol | @codeprogression
75. private Bar cachedBar; public Observable<Bar> getBar(){ if (cachedBar != null){ return Observable.just(cachedBar); } else { return Observable.create(s -> getFooFromWeb()) .subscribeOn(Schedulers.io()) .observeOn(Schedulers.computation()) .map(foo -> calculateBar(foo)) .doOnNext(bar -> cachedBar = bar) } } RxAndroid | Richard Cirerol | @codeprogression
76. Rx in the Android Lifecycle RxAndroid | Richard Cirerol | @codeprogression
77. public void onResume(){ subscription = publisher.getFoo().subscribe(...); } RxAndroid | Richard Cirerol | @codeprogression
78. public void onResume(){ subscription = publisher.getFoo().subscribe(...); } public void onPause(){ subscription.unsubscribe(); } RxAndroid | Richard Cirerol | @codeprogression
79. public void onResume(){ subscription1 = publisher.getFoo().subscribe(...); subscription2 = publisher.getBar().subscribe(...); subscription3 = publisher.getBaz().subscribe(...); } public void onPause(){ subscription1.unsubscribe(); subscription2.unsubscribe(); subscription3.unsubscribe(); } RxAndroid | Richard Cirerol | @codeprogression
80. CompositeSubscription subscriptions; public void onResume(){ subscriptions = new CompositeSubscription(); subscriptions.add(publisher.getFoo().subscribe(...)); subscriptions.add(publisher.getBar().subscribe(...)); subscriptions.add(publisher.getBaz().subscribe(...)); } public void onPause(){ subscriptions.unsubscribe(); } RxAndroid | Richard Cirerol | @codeprogression
81. Warning Once unsubscribed, a CompositeSubscription will not manage any new subscriptions. RxAndroid | Richard Cirerol | @codeprogression
82. Case Study RxAndroid | Richard Cirerol | @codeprogression
83. Case Study Problem: Retrieve a video url for a program RxAndroid | Richard Cirerol | @codeprogression
84. Case Study Problem: Retrieve a video url for a program RxAndroid | Richard Cirerol | @codeprogression
85. Intent intent = new Intent(this, VideoPlayerActivity.class); intent.putExtra("PROGRAM_ID", programId); startActivity(intent); RxAndroid | Richard Cirerol | @codeprogression
86. String id = getIntent().getStringExtra("PROGRAM_ID", id); subscription = publisher.getVideoUrl(id) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new Subscriber<String>(){ @Override public void onCompleted() {} @Override public void onError(final Throwable e) { } @Override public void onNext(final String url) { player.load(url); } }); RxAndroid | Richard Cirerol | @codeprogression
87. Retrofit 4 http://square.github.io/retrofit 4 Type-safe HTTP client 4 RxJava capable (with adapter) RxAndroid | Richard Cirerol | @codeprogression
88. public interface VideoApi { @GET("/video/{id}") Observable<Video> getVideo(@Path("id") String id); } RxAndroid | Richard Cirerol | @codeprogression
89. // VideoService.java public Observable<String> getVideoUrl(String id){ api.getVideo() // return a url from the Video object } RxAndroid | Richard Cirerol | @codeprogression
90. map() Transform each item from one value to another RxAndroid | Richard Cirerol | @codeprogression
91. // VideoService.java public Observable<String> getVideoUrl(String id){ api.getVideo() .map(new Func1<Video, String>{ @Override public String call(Video video){ return video.getUrl(); } }); } RxAndroid | Richard Cirerol | @codeprogression
92. // VideoService.java public Observable<String> getVideoUrl(String id){ api.getVideo() .subscribeOn(Schedules.io) .map(new Func1<Video, String>(){ @Override public String call(Video video){ return video.getUrl(); } }); } RxAndroid | Richard Cirerol | @codeprogression
93. Web service calls aren't that simple. RxAndroid | Richard Cirerol | @codeprogression
94. public interface VideoApi { @GET("/video/{id}") Observable<Video> getVideo( @Header("Authorization") auth, @Path("id") String id); } RxAndroid | Richard Cirerol | @codeprogression
95. public interface VideoApi { @GET("/video/{id}") Observable<Video> getVideo( @Header("Authorization") auth, @Path("id") String id); @POST("/token") Observable<String> getToken(@Body TokenRequest request); } RxAndroid | Richard Cirerol | @codeprogression
96. // VideoService.java public Observable<String> getVideoUrl(String id){ api.getToken(tokenRequest) .subscribeOn(Schedules.io) ... api.getVideo() .map(new Func1<Video, String>{ @Override public String call(Video video){ return video.getUrl(); } }); } RxAndroid | Richard Cirerol | @codeprogression
97. Don't break the chain 4 Use operators to transform RxAndroid | Richard Cirerol | @codeprogression
98. flatMap() Transform each item into one or more Observables, then flatten RxAndroid | Richard Cirerol | @codeprogression
99. // VideoService.java private TokenRequest request; public Observable<String> getVideoUrl(final String id){ api.getToken(tokenRequestBody) .subscribeOn(Schedules.io) .flatMap(new Func1<String, Observable<Video>(){ @Override public Observable<Video> call(String token){ return api.getVideo(token, id); } }) .map(new Func1<Video, String>(){ @Override public String call(Video video){ return video.getUrl(); } }); } RxAndroid | Richard Cirerol | @codeprogression
100. RxAndroid = Observables + Operators + Schedulers + Additional Schedulers RxAndroid | Richard Cirerol | @codeprogression
101. Observables 4 stream data to observers 4 also notify observers of termination events RxAndroid | Richard Cirerol | @codeprogression
102. Operators 4 transform data 4 provide side effects 4 affect either 4 items 4 observable RxAndroid | Richard Cirerol | @codeprogression
103. Schedulers 4 enable concurrency strategies RxAndroid | Richard Cirerol | @codeprogression
104. Subscribers 4 act on the emitted items and notifications 4 are protected from synchronicity or concurrency concerns RxAndroid | Richard Cirerol | @codeprogression
105. http://reactivex.io http://http://blog.danlew.net RxAndroid | Richard Cirerol | @codeprogression
106. Richard Cirerol @codeprogression http://codeprogression.com RxAndroid | Richard Cirerol | @codeprogression
107. Thanks! RxAndroid | Richard Cirerol | @codeprogression