Tango with RxJava

DroidUp Tbilisi and Devfest 2016 presentation talk about RxJava essentials

Transcript

1. Tango with RxJava
2. Tato Kutalia tatocaster @eMoney.ge https://tatocaster.me github.com/tatocaster twitter.com/@TatoKutalia
3. Problems in app • callback-hell • manage tons of async code • error handling • code maintenance
5. Rx
6. Reactive Extensions
7. RxJava
8. What is RxJava Observables Observers Subscribers Schedulers Operators
9. “RxJava is a library that allows us to represent any operation as an asynchronous data stream that can be created on any thread, declaratively composed, and consumed by multiple objects on any thread.”
10. “RxJava is a library that allows us to represent any operation as an asynchronous data stream that can be created on any thread, declaratively composed, and consumed by multiple objects on any thread.” ?
11. What is reactive • programming with asynchronous data streams. • A stream is a sequence of ongoing events ordered in time.
13. Marble Diagram
14. How To Install compile ‘io.reactivex:rxandroid:x.y.z' 
 compile 'io.reactivex:rxjava:x.y.z'
15. Why RxJava • Abstraction of complexity of async data flows and events • Filtering, composition, transformation • Error handling • Light and high performance
16. Observables • This is the data source, the object that will be emitting the sequences of data items that the entities who are interested in the data they provide, will be subscribing. • It implements all the operators mentioned before to be able to transform the data streams. • Observables can be divided in two types: “Hot” observables which might emit data as soon as they are created and “Cold” observables which wait until an Observer subscribes to it.
17. Observers Observers are consumers of an Observable’s asynchronous data stream. Observers can react to the data emitted by the Observable in whatever way they want.
18. Observers
19. Subscribers Subscriber is just an Observer that can, among other things, unsubscribe itself from the items emitted by an Observable.
21. Schedulers • Schedulers determine the thread on which Observables emit their asynchronous data streams and the thread on which Observers consume those data streams. • RxJava allows us to create and consume asynchronous data streams on any thread. Observable.create(new Observable.OnSubscribe<Story>() { //...
 })
 .subscribeOn(Schedulers.io())
 .observeOn(AndroidSchedulers.mainThread());
22. Operators Creating Transforming Filtering Combining Error Handling Conditional Mathematical full list at http://reactivex.io/documentation/operators.html https://github.com/ReactiveX/RxJava/wiki/Alphabetical-List-of-Observable-Operators
23. Operators Operators allow us to declaratively compose Observables An operator is applied to a “source” Observable and it returns a new Observable as a result
24. Operators Observable.create(new Observable.OnSubscribe<Story>() {
 //Emitting story objects...
 })
 .map(new Func1<Story, String>() {
 @Override
 public String call(Story story) {
 return story.getTitle();
 }
 });
25. RxJava in Android
26. RxJava in Android • we don’t control lifecycle • Advantage over AsyncTask, Loader, Handlers
27. Avoiding Memory Leaks Any call to Observable.subscribe() returns a Subscription @Override
 public void onCreate() { //...
 mSubscription = storiesObservable.subscribe(new Observer() {
 @Override
 public void onNext(Story story) {
 Log.d(TAG, story);
 }
 });
 }
 
 @Override
 public void onDestroy() {
 mSubscription.unsubscribe();
 }
28. More for Android RxLifecycle is a project helps Android developers use RxJava within Activity without causing leaks. developed by Trello. https://github.com/trello/RxLifecycle RxBinding by Jake Wharton. Binding API’s for UI widgets. https://github.com/JakeWharton/RxBinding
29. UNLEASH THE BEAST searchViewTextObservable.filter(new Func1<String, Boolean>() { //1
 @Override
 public Boolean call(String s) {
 return s.length() > 2;
 }
 })
 .debounce(QUERY_UPDATE_DELAY_MILLIS, TimeUnit.MILLISECONDS) //2
 .flatMap(new Func1<String, Observable<List<Story>>>() { //3
 @Override
 public Observable<List<Story>> call(String s) {
 return mAdapter.getSearchStoriesObservable(s);
 }
 }
 )
 .subscribeOn(Schedulers.io())
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe(new Observer<List<Story>>() {
 //...
 @Override
 public void onNext(List<Story> stories) {
 mStoriesRecyclerView.setAdapter(new StoryAdapter(stories));
 }
 });
30. UNLEASH THE BEAST searchViewTextObservable.filter(new Func1<String, Boolean>() { //1
 @Override
 public Boolean call(String s) {
 return s.length() > 2;
 }
 })
 .debounce(QUERY_UPDATE_DELAY_MILLIS, TimeUnit.MILLISECONDS) //2 .mergeWith(historicalQueryTappedObservable)
 .flatMap(new Func1<String, Observable<List<Story>>>() { //3
 @Override
 public Observable<List<Story>> call(String s) {
 return mAdapter.getSearchStoriesObservable(s);
 }
 }
 )
 .subscribeOn(Schedulers.io())
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe(new Observer<List<Story>>() {
 //...
 @Override
 public void onNext(List<Story> stories) {
 mStoriesRecyclerView.setAdapter(new StoryAdapter(stories));
 }
 });
31. Convert Async to Rx Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 // Synchronous code written in AsyncTask’s doInBackground()
 }
 })
 .subscribeOn(Schedulers.newThread())
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe();
32. Testing RxJava • comes with TestSubscriber class + jUnit • test Subscription , Observables
33. See More https://github.com/tatocaster/TangoWithRxJava Repo contains a very dumb and simple demonstration of operators and subscriptions (CompositeSubscription) and sample Unit Test
34. People you should follow • David Karnok (project lead of RxJava) • Ivan Morgilo (Author of RxJava essentials) • Jake Wharton (Square) • Dan Lew (Trello) • Artem Zinnatulin
35. Observable.just(“Questions?”)subscribe(new Observer<Object>() { @Override
 public void onNext(Object o) {
 Log.d(TAG, "onNext() called with: o = [" + o + "]");
 }
 @Override
 public void onCompleted() {
 Log.d(TAG, "Thanks");
 }
 @Override
 public void onError(Throwable e) {
 // ignore this shit
 }
 
 }); );