Reactive Programming

Internal talk at Applidium (22 Dec 2015)

Transcript

1. Rx Reactive Extensions 22 décembre 2015
2. Problems to solve • Callback hell
3. Problems to solve • Callback hell • Chaining operations
4. Problems to solve • Callback hell • Chaining operations
5. Problems to solve • Callback hell • Chaining operations • Threading is hard
6. Problems to solve • Callback hell • Chaining operations • Threading is hard CompletionService Delayed Executor ExecutorService Future RunnableFuture ScheduledExecutorService ScheduledFuture ThreadFactory BrokenBarrierException CountDownLatch CyclicBarrier Exchanger ForkJoinPool ForkJoinWorkerThread Phaser RecursiveAction RecursiveTask ScheduledThreadPoolExecutor Semaphore Thread AsyncTask Loader IntentService
7. Problems to solve • Callback hell • Chaining operations • Threading is hard • Error handling
8. Example: MyMTV Login Account User User User User User Profile Profile Profile Profile Profile Success!
9. Example: RMN Slideshow: - collection of medias (images and videos) - images should be displayed as such - videos should display a preview
10. Reactive Extensions
11. Rx: Reactive Extensions • Functional Reactive Programming : 1997 (40 years after Functional/OOP) • Started by Microsoft for .NET • RxJava: 2012 (Netflix) => ReactiveCocoa, RxAndroid
12. Observable Pattern
13. Observable single items multiple items synchronous T getData() Iterable<T> getData() Collection<T> getData() asynchronous Future<T> getData() Observable<T> getData()
14. Subscriber event Iterable (pull) Observable (push) retrieve data T next() onNext(T) discover error throws Exception onError(Exception) complete returns onCompleted()
15. Observable Pattern
16. Creating an Observable Observable<String> o = Observable.from("a", "b", "c"); def list = [5, 6, 7, 8] Observable<Integer> o = Observable.from(list); Observable<String> o = Observable.just("one object");
17. Creating an Observable Observable.just(t); Observable.just(t1, t2, t3, t4, t5, ...); Observable.from(iterable); Observable.range(start, end); Observable.empty(); Observable.error(throwable); Observable.never(); Observable.interval(interval, unit); Observable.timer(delay, period, unit);
18. Creating an Observable func myJust<E>(element: E) -> Observable<E> { return create { observer in observer.on(.Next(element)) observer.on(.Completed) return NopDisposable.instance } } myJust(0) .subscribeNext { n in print(n) }
19. “Warmth” of an Observable
20. Operators
21. Observable Pattern
22. Visualising operators
23. map
24. flatMap
25. Solving RMN Observable<Media> medias = apiManager.getMediaSlideshow(exposition); Observable<URL> urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );
26. Solving RMN Observable<Media> medias = apiManager.getMediaSlideshow(exposition); Observable<URL> urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );
27. Solving RMN Observable<Media> medias = apiManager.getMediaSlideshow(exposition); Observable<URL> urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );
28. Solving RMN Observable<Media> medias = apiManager.getMediaSlideshow(exposition); Observable<URL> urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );
29. Solving RMN Observable<Media> medias = apiManager.getMediaSlideshow(exposition); Observable<URL> urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );
30. filter
31. Solving MyMTV Login Account User User User User User Profile Profile Profile Profile Profile Success!
32. Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);
33. Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);
34. Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);
35. Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);
36. Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);
37. Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);
38. Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);
39. Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);
40. Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);
41. merge
42. merge vs concat
43. concat example // Our sources Observable<Data> memory = ...; Observable<Data> disk = ...; Observable<Data> network = ...; // Retrieve the first source with data Observable<Data> source = Observable .concat(memory, disk, network) .first();
44. flatMap vs concatMap
45. switchMap
46. skip
47. distinct
48. distinctUntilChanged
49. retryWhen
50. defaultIfEmpty - switchIfEmpty
51. debounce
52. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
53. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
54. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
55. debounce
56. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
57. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
58. switchMap - switchOnNext
59. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
60. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
61. retryWhen
62. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
63. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
64. Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());
65. timeout
66. zip
67. combineLatest
68. combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each
69. combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each
70. combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each
71. combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each
72. combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each
73. combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each
74. combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each
75. Threading (and more)
76. subscribeOn / observeOn myObservableServices.retrieveImage(url) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(bitmap -> myImageView.setImageBitmap(bitmap));
77. subscribeOn / observeOn
78. subscribeOn / observeOn <T> Transformer<T, T> applySchedulers() { return observable -> observable.subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); } Observable.from(someSource) .map(data -> manipulate(data)) .compose(applySchedulers()) .subscribe(data -> doSomething(data));
79. subscribeOn / observeOn <T> Transformer<T, T> applySchedulers() { return observable -> observable.subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); } Observable.from(someSource) .map(data -> manipulate(data)) .compose(applySchedulers()) .subscribe(data -> doSomething(data));
80. <T> Transformer<T, T> applySchedulers() { return observable -> observable.subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); } Observable.from(someSource) .map(data -> manipulate(data)) .compose(applySchedulers()) .subscribe(data -> doSomething(data)); subscribeOn / observeOn
81. private Object slowBlockingMethod() { ... } public Observable<Object> newMethod() { return Observable.defer(() -> Observable.just(slowBlockingMethod())); } defer
82. Cancelling subscriptions @Override public void onStart() { super.onStart(); mSubscriptions = new CompositeSubscription(); mSubscriptions.add(rxBus.toObserverable().subscribe(new Action1<Object>() { @Override public void call(Object event) { // ... }})); } @Override public void onStop() { super.onStop(); mSubscriptions.unsubscribe(); }
83. Side effect operations observable.doOnSubscribe(action0); observable.doOnUnsubscribe(action0); observable.doOnNext(action1); observable.doOnCompleted(action0); observable.doOnError(action0); observable.doOnTerminate(action0); // before termination methods observable.finallyDo(action0); // after termination methods observable.doOnEach(action1); // next, completed or error observable.doOnRequest(action1);
84. cache
85. cache Observable<Photo> request = service.getUserPhoto(id).cache(); Subscription sub = request.subscribe(photo -> handleUserPhoto(photo)); // ...When the Activity is being recreated... sub.unsubscribe(); // ...Once the Activity is recreated... request.subscribe(photo -> handleUserPhoto(photo));
86. cache
87. publish
88. back pressure
89. Questions? 22 décembre 2015