Artur Glier - Schibsted Tech Polska - Learn you some rx for the greater good

1. Artur Glier

2. RxJava – Reactive Extensions for the JVM – a library for
composing asynchronous and event-based programs using
observable sequences for the Java VM

5. ✓ Microsoft Reactive Extensions by Erik Meijer
Fast forward

6. ✓ Microsoft Reactive Extensions by Erik Meijer
✓ Netflix RxJava & RxJs by Ben Christensen
Fast forward

7. ✓ Microsoft Reactive Extensions by Erik Meijer
✓ Netflix RxJava & RxJs by Ben Christensen
✓ Github ReactiveCocoa
Fast forward

8. ✓ Microsoft Reactive Extensions by Erik Meijer
✓ Netflix RxJava & RxJs by Ben Christensen
✓ Github ReactiveCocoa (Think different...)
Fast forward

9. Some of early adopters

10. RxJava is all about FRP

11. ✓ Programming with
asynchronous data streams
FRP is...

12. ✓ Programming with
asynchronous data streams
+
✓ Toolbox
FRP is...

13. ✓ Cross platform ;)
✓ A fun new tool. “If you only have a hammer -
you tend to see each problem as nail.”
✓ Less error prone
✓ ! a steep learning curve
FRP is...

14. @interface RACSignal (Operations)
- (RACSignal *)doNext:(void (^)(id x))block;
- (RACSignal *)doError:(void (^)(NSError *error))block;
- (RACSignal *)doCompleted:(void (^)(void))block;
- (RACSignal *)throttle:(NSTimeInterval)interval;
- (RACSignal *)throttle:(NSTimeInterval)interval valuesPassingTest:(BOOL (^)(id next))predicate;
- (RACSignal *)delay:(NSTimeInterval)interval;
- (RACSignal *)repeat;
- (RACSignal *)initially:(void (^)(void))block;
- (RACSignal *)finally:(void (^)(void))block;
- (RACSignal *)bufferWithTime:(NSTimeInterval)interval onScheduler:(RACScheduler *)scheduler;
- (RACSignal *)collect;
- (RACSignal *)takeLast:(NSUInteger)count;
- (RACSignal *)combineLatestWith:(RACSignal *)signal;
+ (RACSignal *)combineLatest:(id<NSFastEnumeration>)signals;
+ (RACSignal *)combineLatest:(id<NSFastEnumeration>)signals reduce:(id (^)())reduceBlock;
- (RACSignal *)merge:(RACSignal *)signal;
+ (RACSignal *)merge:(id<NSFastEnumeration>)signals;
- (RACSignal *)flatten:(NSUInteger)maxConcurrent;
...
@end

15. RxJava is an extension of the
observer desing pattern

18. It’s pull-based approach and any logic
requires the result to be available at
execution time
Iterables

19. Futures are straight-forward to use for a
single level of asynchronous execution
Conditional asynchronous execution flows
become difficult to optimally compose
Futures

20. They are easy to use with a single level of
asynchronous execution but become
unwieldy with nested composition.
Callbacks

21. Producer can signal consumer that there is
no more data available
Producer can signal consumer that error has
ocurred
Observer Pattern

22. How do you learn RxJava?

23. BY example

24. RxJava is all about FRP

25. FRP is...
✓ Responsive, Reslient,
Elastic, Message Driven
“FRP manifesto”
✓ Rx = Observables + LINQ + Schedulers
“Microsoft”
✓ Programming paradigm for reactive programming using
the building blocks of functional programming
“Wikipedia”
✓ … “stackoverflow”

26. FRP is...
✓ Responsive, Reslient,
Elastic, Message Driven
“FRP manifesto”
✓ Rx = Observables + LINQ + Schedulers
“Microsoft”
✓ Programming paradigm for reactive programming using
the building blocks of functional programming
“Wikipedia”
✓ … “stackoverflow”

27. FRP is...
✓ Responsive, Reslient,
Elastic, Message Driven
“FRP manifesto”
✓ Rx = Observables + LINQ + Schedulers
“Microsoft”
✓ Programming paradigm for reactive programming using
the building blocks of functional programming
“Wikipedia”
✓ … “stackoverflow”

28. FRP is...
✓ Responsive, Reslient,
Elastic, Message Driven
“FRP manifesto”
✓ Rx = Observables + LINQ + Schedulers
“Microsoft”
✓ Programming paradigm for reactive programming using
the building blocks of functional programming
“Wikipedia”
✓ … “stackoverflow”

29. FRP is...
✓ Responsive, Reslient,
Elastic, Message Driven
“FRP manifesto”
✓ Rx = Observables + LINQ + Schedulers
“Microsoft”
✓ Programming paradigm for reactive programming using
the building blocks of functional programming
“Wikipedia”
✓ … “stackoverflow”
Bla, bla,
bla...

30. Rx.Observable.prototype
.flatMapLatest(selector, [thisArg])
Projects each element of an observable sequence into a new
sequence of observable sequences by incorporating the element's
index and then transforms an observable sequence of observable
sequences into an observable sequence producing values only from
the most recent observable sequence.

32. BY example

33. RxJava is all about marbles

34. Not this kind of marbles

35. This kind of marbles

36. RxJava is all about code

37. Observable<String> observable = Observable.just("Hello, World!");

38. Subscriber<String> subscriber = new Subscriber<String>() {
@Override
public void onCompleted() {
// code here
}
@Override
public void onError(Throwable e) {
// code here
}
@Override
public void onNext(String s) {
output.append(String.format("%sn", s));
}
};

39. @Override
protected void onStart() {
super.onStart();
observable
.observeOn(Schedulers.newThread())
.subscribeOn(AndroidSchedulers.mainThread())
.subscribe(subscriber);
}

43. Request composition
public interface AftonbladetAPI {
@GET("/item/{id}.json")
Observable<Item> item(@Path("id") long id);
@GET("/topstories.json")
Observable<List<Long>> topStories();
}

44. Request composition
GET /topstories
[ 8414149, 8414078, 8413972, 8411638, 8414102, 8413204, 8413100, 8413971,
8412744, 8414003, 8412841, 8412802, 8412605, 8413548, 8413123, 8414437,
8412897, 8413028, 8413341, 8412425, 8411762, 8413623, 8412346, 8411356,
8413056, 8413365, 8412372, 8414055, 8412877, 8412167, 8413264, 8414137,
8410519, 8412933, 8411846, 8412929, 8411254, 8411512, 8412777, 8412626,
8413274, 8414389, 8414117, 8412114, 8412212, 8412759, 8412696, 8412768,
8411643, 8411866, 8413966, 8410976, 8410545, 8410358, 8413979, 8414129,
8411791, 8409075, 8410314, 8411532, 8411553, 8412099, 8412085, 8410356,
8409084, 8412862, 8409823, 8412705, 8410220, 8409323, 8414090, 8410326 ]

45. Request composition
GET item/8863.json
{
"by": "Daniel Söderbäck",
"id": 1,
"score": 111,
"time": 1415793648,
"title": "Swede Jacobson won the Poker World Championships",
"type": "story",
"url": "http://www.aftonbladet.se/sportbladet/poker/article19844615.ab"
}

46. Request composition
public void onRefresh() {
Aftonbladet.API.topStories()
.flatMap(longs -> Observable.from(longs))
.flatMap(id -> Aftonbladet.API.item(id))
.collect(new ArrayList<Item>(), (items, item) -> items.add(item))
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}

47. Request composition - flatMap()
public void onRefresh() {
Aftonbladet.API.topStories()
.flatMap(longs -> Observable.from(longs))
.flatMap(id -> Aftonbladet.API.item(id))
.collect(new ArrayList<Item>(), (items, item) -> items.add(item))
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}

48. Request composition - flatMap()
public void onRefresh() {
Aftonbladet.API.topStories()
.flatMap(longs -> Observable.from(longs))
.flatMap(id -> Aftonbladet.API.item(id))
.collect(new ArrayList<Item>(), (items, item) -> items.add(item))
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}

49. Request composition - collect()
public void onRefresh() {
Aftonbladet.API.topStories()
.flatMap(longs -> Observable.from(longs))
.flatMap(id -> Aftonbladet.API.item(id))
.collect(new ArrayList<Item>(), (items, item) -> items.add(item))
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}

50. Request composition - threads
public void onRefresh() {
Aftonbladet.API.topStories()
.flatMap(longs -> Observable.from(longs))
.flatMap(id -> Aftonbladet.API.item(id))
.collect(new ArrayList<Item>(), (items, item) -> items.add(item))
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}

51. Request composition
public void onRefresh() {
Aftonbladet.API.topStories()
.flatMap(longs -> Observable.from(longs))
.flatMap(id -> Aftonbladet.API.item(id))
.collect(new ArrayList<Item>(), (items, item) -> items.add(item))
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}

52. Request composition
.subscribe(
items -> list.setAdapter(new ArrayAdapter<Item>(..., ..., items)),
error -> handleError(error),
() -> {
if (ptr.isRefreshing()) ptr.setRefreshing(false);
}
)

54. Request composition - filter()
public void onRefresh() {
HackerNews.API.topStories()
.flatMap(longs -> Observable.from(longs))
.flatMap(id -> HackerNews.API.item(id))
.filter(item -> item.time > 1412985600)
.collect(new ArrayList<Item>(), (items, item) -> items.add(item))
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}

56. Request composition - limit()
public void onRefresh() {
HackerNews.API.topStories()
.flatMap(longs -> Observable.from(longs))
.flatMap(id -> HackerNews.API.item(id))
.filter(item -> item.time > 1412985600)
.limit(10)
.collect(new ArrayList<Item>(), (items, item) -> items.add(item))
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}

58. Request composition
Observable.zip(
service.getUserPhoto(id),
service.getPhotoMetadata(id),
(photo, metadata) -> createPhotoWithData(photo, metadata))
.subscribe(photoWithData -> showPhoto(photoWithData));

60. public static Observable<String> getRegIdObservable(final Context context) {
return Observable.create(new Observable.OnSubscribe<String>() {
@Override
public void call(Subscriber<? super String> subscriber) {
try {
subscriber.onNext(getDeviceRegId(context));
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
}
});
}

61. GcmUtils.getRegIdObservable(this)
.subscribeOn(Schedulers.newThread())
.observeOn(Schedulers.newThread())
.subscribe(new Action1<Topic>() {
@Override
public void call(Topic topic) {
API.subscribeToTopic(/* ... */);
}
});

63. RxJava is all about fun

64. ✓ https://gist.github.
com/vizZ/9756d2e2450a7ef9f744
Any advice?

65. Questions?
artur.glier@schibsted.pl

67. Refactoring Android to RxJava