Introduction to RxJava (Android Istanbul Meetup, 2016)

Transcript

1. Introduction to RxJava Doruk Kangal Alper Cem Polat
2. Reactive Programming • Reactive programming is programming with asynchronous data streams. • On top of that, there is an amazing toolbox of functions to combine, create and filter any of those streams.
3. Reactive Mantra
4. Why RxJava? • Easy threading • Set of powerful operators • Explicit Error Handling • Easy implementation of data flows • Chain method calls • Reduce boilerplate code
5. The Basics
6. Hello World //Create an observable that emits "Hello World" and completes Observable<String> myObservable = Observable.create(new Observable.OnSubscribe<String>() { @Override public void call(Subscriber<? super String> subscriber) { subscriber.onNext("Hello world!"); subscriber.onCompleted(); } });
7. Hello World //Create a subscriber that prints each String emitted by the Observable. Subscriber<String> mySubscriber = new Subscriber<String>() { @Override public void onCompleted() { } @Override public void onError(Throwable e) { } @Override public void onNext(String s) { System.out.println(s); } };
8. Hello World //Create a subscriber that prints each String emitted by the Observable. Subscriber<String> mySubscriber = new Subscriber<String>() { @Override public void onCompleted() { } @Override public void onError(Throwable e) { } @Override public void onNext(String s) { System.out.println(s); } }; //Hook them each other with subscribe. myObservable.subscribe(mySubscriber);
9. Hello World - Simpler Observable<String> justObservable = Observable.just("Hello World!");
10. Hello World - Simpler Observable<String> justObservable = Observable.just("Hello World!"); Action1<String> onNextAction = new Action1<String>() { @Override public void call(String s) { System.out.println(s); } };
11. Hello World - Simpler Observable<String> justObservable = Observable.just("Hello World!"); Action1<String> onNextAction = new Action1<String>() { @Override public void call(String s) { System.out.println(s); } }; justObservable.subscribe(onNextAction);
12. Hello World - Simpler Observable<String> justObservable = Observable.just("Hello World!"); Action1<String> onNextAction = new Action1<String>() { @Override public void call(String s) { System.out.println(s); } }; justObservable.subscribe(onNextAction); Observable.just("Hello World!") .subscribe(new Action1<String>() { @Override public void call(String s) { System.out.println(s); } });
13. Hello World - Simpler Observable<String> justObservable = Observable.just("Hello World!"); Action1<String> onNextAction = new Action1<String>() { @Override public void call(String s) { System.out.println(s); } }; justObservable.subscribe(onNextAction); Observable.just("Hello World!") .subscribe(new Action1<String>() { @Override public void call(String s) { System.out.println(s); } }); Observable.just("Hello World!") .subscribe(s -> System.out.println(s));
14. Transformation Observable.just("Hello world! - Alper") .subscribe(s -> System.out.println(s));
15. Transformation Observable.just("Hello world! - Alper") .subscribe(s -> System.out.println(s)); Observable.just("Hello world!") .subscribe(s -> System.out.println(s + " - Alper"));
16. Marble Diagram
17. Map Operator Observable.just("Hello, world!") .map(new Func1<String, String>() { @Override public String call(String s) { return s + " - Alper"; } }) .subscribe(s -> System.out.println(s));
18. Map Operator Observable.just("Hello, world!") .map(new Func1<String, String>() { @Override public String call(String s) { return s + " - Alper"; } }) .subscribe(s -> System.out.println(s)); Observable.just("Hello, world!") .map(s -> s + " - Alper") .subscribe(s -> System.out.println(s));
19. Map Operator Observable.just("Hello, world!") .map(new Func1<String, Integer>() { @Override public Integer call(String s) { return s.length(); } }) .subscribe(i -> System.out.println(Integer.toString(i)));
20. Map Operator Observable.just("Hello, world!") .map(new Func1<String, Integer>() { @Override public Integer call(String s) { return s.length(); } }) .subscribe(i -> System.out.println(Integer.toString(i))); Observable.just("Hello, world!") .map(s -> s.length()) .subscribe(i -> System.out.println(Integer.toString(i)));
21. Map Operator Observable.just("Hello, world!") .map(new Func1<String, Integer>() { @Override public Integer call(String s) { return s.length(); } }) .subscribe(i -> System.out.println(Integer.toString(i))); Observable.just("Hello, world!") .map(s -> s.length()) .subscribe(i -> System.out.println(Integer.toString(i))); Observable.just("Hello, world!") .map(s -> s.length()) .map(i -> Integer.toString(i)) .subscribe(s -> System.out.println(s));
22. More Operators //Returns list of contributers of a Github repo Observable<List<String>> getContributers(String repo);
23. More Operators getContributers("rxjava") .subscribe(contributers -> { for (String contributer : contributers) { System.out.println(contributer); } });
24. From Operator List<String> list = Arrays.asList("contributer1", "contributer2", "contributer3"); Observable.from(list) .subscribe(contributer -> System.out.println(contributer));
25. From Operator List<String> list = Arrays.asList("contributer1", "contributer2", "contributer3"); Observable.from(list) .subscribe(contributers -> System.out.println(contributers)); getContributers("rxjava").subscribe(contributers -> { Observable.from(contributers) .subscribe(contributer -> System.out.println(contributer)); });
26. FlatMap Operator getContributers("rxjava") .flatMap(new Func1<List<String>, Observable<String>>() { @Override public Observable<String> call(List<String> contributers) { return Observable.from(contributers); } }) .subscribe(contributer -> System.out.println(contributer));
27. FlatMap Operator getContributers("rxjava") .flatMap(new Func1<List<String>, Observable<String>>() { @Override public Observable<String> call(List<String> contributers) { return Observable.from(contributers); } }) .subscribe(contributer -> System.out.println(contributer)); getContributers("rxjava") .flatMap(contributers -> Observable.from(contributers)) .subscribe(contributer -> System.out.println(contributer));
28. FlatMap Operator //Returns number of commits of a given user Observable<Integer> getCommitCount(String user);
29. FlatMap Operator //Returns number of commits of a given user Observable<Integer> getCommitCount(String user); getContributers("rxjava") .flatMap(contributers -> Observable.from(contributers)) .flatMap(new Func1<String, Observable<Integer>>() { @Override public Observable<Integer> call(String user) { return getCommitCount(user); } }) .subscribe(commitCount -> System.out.println(commitCount));
30. FlatMap Operator //Returns number of commits of a given user Observable<Integer> getCommitCount(String user); getContributers("rxjava") .flatMap(contributers -> Observable.from(contributers)) .flatMap(new Func1<String, Observable<Integer>>() { @Override public Observable<Integer> call(String user) { return getCommitCount(user); } }) .subscribe(commitCount -> System.out.println(commitCount)); getContributers("rxjava") .flatMap(contributers -> Observable.from(contributers)) .flatMap(user -> getCommitCount(user)) .subscribe(commitCount -> System.out.println(commitCount));
31. Filter Operator getContributers("rxjava") .flatMap(contributers -> Observable.from(contributers)) .flatMap(user -> getCommitCount(user)) .filter(new Func1<Integer, Boolean>() { @Override public Boolean call(Integer commitCount) { return commitCount > 0; } }) .subscribe(commitCount -> System.out.println(commitCount));
32. Filter Operator getContributers("rxjava") .flatMap(contributers -> Observable.from(contributers)) .flatMap(user -> getCommitCount(user)) .filter(new Func1<Integer, Boolean>() { @Override public Boolean call(Integer commitCount) { return commitCount > 0; } }) .subscribe(commitCount -> System.out.println(commitCount)); getContributers("rxjava") .flatMap(contributers -> Observable.from(contributers)) .flatMap(user -> getCommitCount(user)) .filter(commitCount -> commitCount > 0) .subscribe(commitCount -> System.out.println(commitCount));
33. Take Operator getContributers("rxjava") .flatMap(contributers -> Observable.from(contributers)) .flatMap(user -> getCommitCount(user)) .filter(commitCount -> commitCount > 0) .take(5) .subscribe(commitCount -> System.out.println(commitCount));
34. doOnNext Operator getContributers("rxjava") .flatMap(contributers -> Observable.from(contributers)) .flatMap(user -> getCommitCount(user)) .filter(commitCount -> commitCount > 0) .take(5) .doOnNext(commitCount -> saveToDisk(commitCount)) .subscribe(commitCount -> System.out.println(commitCount));
35. Threading myObservableServices.retrieveImage(url) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(bitmap -> myImageView.setImageBitmap(bitmap));
36. Threading Output Filter1: pool-1-thread-3 Map1: pool-1-thread-3 Filter2: pool-1-thread-4 OnCompleted: pool-1-thread-4 Map2: RxCachedThreadScheduler-1 onNext: RxCachedThreadScheduler-1 onComplete: RxCachedThreadScheduler-1 Observable.just("Hello") .filter(s1 -> true) .subscribeOn(Schedulers.newThread()) .map(s -> s.length()) .subscribeOn(Schedulers.io()) .observeOn(Schedulers.newThread()) .doOnCompleted(() -> { System.out.printf("OnCompleted: %s", currentThread().getName()); }) .filter(s1 -> true) .observeOn(Schedulers.io()) .map(length -> String.valueOf(length)) .subscribe(length -> { System.out.printf("onNext: %s", currentThread().getName()); }, throwable -> { System.out.printf("onError: %s", currentThread().getName()); }, () -> { System.out.printf("onComplete: %s", currentThread().getName()); });
37. Subscription Subscription subscription = Observable.just("Hello, World!") .subscribe(s -> System.out.println(s)); //Breaks the chain subscription.unsubscribe(); //Returns true System.out.println(subscription.isUnsubscribed());
38. Error Handling Observable.just("Hello, world!") .map(s -> methodThatCanThrowException(s)) .map(s -> otherMethodThatCanThrowException(s)) .subscribe(new Subscriber<String>() { @Override public void onNext(String s) { System.out.println(s); } @Override public void onCompleted() { System.out.println("Completed!"); } @Override public void onError(Throwable e) { System.out.println(e.getMessage()); } });
39. Error Handling - Fallback Observable<BaseAccount> observable = getAccount(accountId); observable.onErrorResumeNext(t -> { return Observable.just(BaseAccount.DEFAULT); }) .subscribe(p -> System.out.println(p));
40. Error Handling - Retry Observable<BaseAccount> observable = getAccount(accountId); observable.retry((retryCount, throwable) -> { System.out.println("Error occurred when retrieving account" + throwable.getMessage()); return retryCount < 2 ? Boolean.TRUE : Boolean.FALSE; }) .subscribe(s -> System.out.println(s));
41. Demo
42. Q & A