Android Lx - 25 Jan 2017 - RxJava: More than the basic

Transcript

1. RxJava: more than the basic Sérgio Moura : sergiomarquesmoura : sergiomarqmoura
2. Wrap your app’s callback APIs with RxJava Why? - Android apps’ event-based fashion - Many 3rd party APIs: - Work assynchronously - Can be modeled by a stream of events - Preventing ending up with “callback hells”
3. 1. TwitterApi twitterApi = TwitterApiFactory().getInstance(); 2. 3. button.setOnClickListener(view -> { 4. twitterApi.getTweets(new TweetListener() { 5. 6. @Override 7. public void onTweetReceived(Tweet tweet) { 8. latestTweet.setText(tweet.getContent()); 9. } 10. 11. @Override 12. public void onError(Exception exception) { 13. latestTweet.setText("Error getting tweets! Cause: " + exception.getMessage()); 14. } 15. }); 16. }); • Too much code • Poorly readable • Hinders multithreading • No separation between technical and business domains
4. Using rx.Observable.create()
5. 1. public class RxTwitterInteractor { 2. 3. Observable<Tweet> observe() { 4. return Observable.create(subscriber -> { 5. TwitterApi twitterApi = new TwitterApiFactory().getInstance(); 6. 7. twitterApi.getTweets(new TweetListener() { 8. @Override 9. public void onTweetReceived(Tweet tweet) { 10. subscriber.onNext(tweet); 11. } 12. 13. @Override 14. public void onError(Throwable throwable) { 15. subscriber.onError(throwable); 16. } 17. }); 18. 19. subscriber.add(Subscriptions.create(twitterApi::shutdown)); 20. }); 21. } 22. } Automatic resource cleanup on unsubscription
6. 1. CompositeSubscription subscriptions = new CompositeSubscription(); 2. 3. subscriptions.add(rxTwitterInteractor.observe() 4. .subscribeOn(Schedulers.io()) 5. .observeOn(AndroidSchedulers.mainThread()) 6. .subscribe(new Subscriber<Tweet>() { 7. @Override 8. public void onCompleted() { 9. // empty 10. } 11. 12. @Override 13. public void onError(Throwable e) { 14. view.showError(e); 15. } 16. 17. @Override 18. public void onNext(Tweet tweet) { 19. view.displayTweet(tweet); 20. } 21. })); Better, but.. • Every subscriber still opens a new connection • The observable instance should be reusable
7. Using rx.Subject
8. 1. class RxTwitterSubject { 2. 3. private final PublishSubject<Tweet> subject = PublishSubject.create(); 4. 5. public RxTwitterSubject() { 6. TwitterApi twitterApi = new TwitterApiFactory().getInstance(); 7. 8. twitterApi.getTweets(new TweetListener() { 9. @Override 10. public void onTweetReceived(Tweet tweet) { 11. subject.onNext(tweet); 12. } 13. 14. @Override 15. public void onError(Throwable throwable) { 16. subject.onError(throwable); 17. } 18. }); 19. } 20. 21. public Observable<Tweet> observe() { 22. return subject; 23. } 24. } Treating subject as an Observable Treating subject as an Observer • Only one reusable connection • Every Subscriber will receive subsequent events after subscribing
9. rx.Subject flavors • AsyncSubject ◦ Remembers the last emitted value, only pushes to every subscriber when onComplete() is called • BehaviorSubject ◦ Emits the most recent event on subscription, and every subsequent event after that • ReplaySubject ◦ Caches all events pushed through it, emits them all before real-time events to every new subscriber ◦ ReplaySubject.createWithSize(int n) ◦ ReplaySubject.createWithTime(long time) ◦ ReplaySubject.createWithTimeAndSize(long time, int n)
10. Using rx.Completable Because not everything must have a type
11. 1. class RxTwitterSubject { 2. 3. ... 4. 5. public Observable<Tweet> observe() { 6. return subject; 7. } 8. 9. public Completable init() { 10. twitterApi.init("MyApiKey"); 11. 12. twitterApi.getTweets(new TweetListener() { 13. @Override 14. public void onTweetReceived(Tweet tweet) { 15. subject.onNext(tweet); 16. } 17. 18. @Override 19. public void onError(Throwable throwable) { 20. subject.onError(throwable); 21. } 22. }); 23. 24. return Completable.complete(); 25. } 26. } Notifying the initialization completion 1. subscriptions.add(rxTwitterSubject.init() 2. .andThen(rxTwitterSubject.observe()) 3. .subscribeOn(Schedulers.io())
12. Using rx.Single Because not everything is a stream
13. 1. subscriptions.add(rxTwitterSubject.init() 2. .andThen(rxTwitterSubject.getCount()) 3. .flatMapObservable(count -> rxTwitterSubject.observe()) 4. .subscribeOn(Schedulers.io()) 1. class RxTwitterSubject { 2. 3. private final PublishSubject<Tweet> subject = PublishSubject.create(); 4. 5. public RxTwitterSubject() { 6. TwitterApi twitterApi = new TwitterApiFactory().getInstance(); 7. } 8. 9. public Observable<Tweet> observe() { 10. return subject; 11. } 12. 13. ... 14. 15. public Single getCount() { 16. return Single.just(subject.count()); 17. } 18. }
14. Monitoring and debugging streams with doOn...
15. Why doOn…() callbacks? • Don’t change an Observable state • Return the same Observable
16. 1. subscriptions.add(rxTwitterSubject.init() 2. .andThen(rxTwitterSubject.getCount()) 3. .flatMapObservable(count -> rxTwitterSubject.observe()) 4. .doOnSubscribe(() -> log("Subscribed to the tweets...")) 5. .subscribeOn(Schedulers.io()) 6. .observeOn(AndroidSchedulers.mainThread())
17. 1. subscriptions.add(rxTwitterSubject.init() 2. .andThen(rxTwitterSubject.getCount()) 3. .flatMapObservable(count -> rxTwitterSubject.observe()) 4. .doOnSubscribe(() -> log("Subscribed to the tweets...")) 5. .doOnNext(tweet -> view.displayTweet(tweet)) 6. .subscribeOn(Schedulers.io()) 7. .observeOn(AndroidSchedulers.mainThread()) Where’s the problem?
18. 1. subscriptions.add(rxTwitterSubject.init() 2. .andThen(rxTwitterSubject.getCount()) 3. .flatMapObservable(count -> rxTwitterSubject.observe()) 4. .doOnSubscribe(() -> log("Subscribed to the tweets...")) .observeOn(AndroidSchedulers.mainThread()) 5. .doOnNext(tweet -> view.displayTweet(tweet)) 6. .subscribeOn(Schedulers.io())
19. 1. subscriptions.add(rxTwitterSubject.init() 2. .andThen(rxTwitterSubject.getCount()) 3. .flatMapObservable(count -> rxTwitterSubject.observe()) 4. .doOnSubscribe(() -> log("Subscribed to the tweets...")) 5. .observeOn(AndroidSchedulers.mainThread()) 6. .doOnNext(tweet -> view.displayTweet(tweet)) 7. .doOnCompleted(() -> log("Finished fetching tweets!")) 8. .subscribeOn(Schedulers.io())
20. 1. subscriptions.add(rxTwitterSubject.init() 2. .andThen(rxTwitterSubject.getCount()) 3. .flatMapObservable(count -> rxTwitterSubject.observe()) 4. .doOnSubscribe(() -> log("Subscribed to the tweets...")) 5. .observeOn(AndroidSchedulers.mainThread()) 6. .doOnNext(tweet -> view.displayTweet(tweet)) 7. .doOnCompleted(() -> log("Finished fetching tweets!")) 8. .doOnError(throwable -> log("Error: "+throwable.getMessage())) 9. .subscribeOn(Schedulers.io())
21. 1. subscriptions.add(rxTwitterSubject.init() 2. .andThen(rxTwitterSubject.getCount()) 3. .flatMapObservable(count -> rxTwitterSubject.observe()) 4. .doOnSubscribe(() -> log("Subscribed to the tweets...")) 5. .observeOn(AndroidSchedulers.mainThread()) 6. .doOnNext(tweet -> view.displayTweet(tweet)) 7. .doOnCompleted(() -> log("Finished fetching tweets!")) 8. .doOnError(throwable -> log("Error: "+throwable.getMessage())) 9. .onErrorReturn(new Tweet("This is the end!")) 10. .subscribeOn(Schedulers.io())
22. Thank you for coming! Questions?