The original slide is here... http://misgod.github.io/Slide-FRP-Android Introduce to Functional Reactive Programming on Android with RxJava/RxAndroid.

1. Functional Reactive Programming on
Android
Sam Lee
2014/11/22 @Mosut x Taina.py x FP
http://misgod.github.io/Slide-FRP-Android/ 第 1 ⾴

2. About Me
Sam Lee (misgod.tw@gmail.com)
A software engineer lives in Tainan
Work for htc
Most used Clojure, Scala and Java
Interested in Functional Programming
Interested in Machine Learning and Data Analyst
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http://misgod.github.io/Slide-FRP-Android/ 第 2 ⾴

3. What Is Functional Reactive Programming
A style of programming based on two key ideas: continuous time-varying behaviors, and
event-based reactivity
Try it
aObservable.map(x -> x*x) //Square
.reduce((a, b) -> a+b) //Sum
.subscribe(x -> println(x)); //Show
http://misgod.github.io/Slide-FRP-Android/ 第 3 ⾴

4. Why Functional Reactive Programming
Writing concurrent programs · correct is di2cult.
You can transform & compose asynchronous operations.
High-level abstractions
Standard error handling
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http://misgod.github.io/Slide-FRP-Android/ 第 4 ⾴

5. Say Hello to Rx family
Java: RxJava
Scala: RxScala
Clojure: RxClojure
Groovy: RxGroovy
JRuby: RxJRuby
JavaScript: RxJS
C#: Rx.NET
C#(Unity): UniRx
C++: RxCpp
Ruby: Rx.rb
Python: RxPY
Kotlin: RxKotlin
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http://misgod.github.io/Slide-FRP-Android/ 第 5 ⾴

6. Introduce to RxJava
https://github.com/ReactiveX/RxJava
RxJava is a JVM implementation of Reactive Extensions
RxJava extends Observer pattern to support data/event and compose operators in
abstract.
Built by NetBix
Support Java 6+ & Android 2.3+
Java 8 lambda support
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http://misgod.github.io/Slide-FRP-Android/ 第 6 ⾴

7. Asynchronous sequences of multiple items
SINGLE ITEMS MULTIPLE ITEMS
synchronous T getData() Iterable<T> getData()
asynchronous Future<T> getData() Observable<T> getData()
http://misgod.github.io/Slide-FRP-Android/ 第 7 ⾴

8. Observable is "dual" to Iterable
EVENT ITERABLE (PULL) OBSERVABLE (PUSH)
retrieve data T next() onNext(T)
discover error throws Exception onError(Exception)
complete !hasNext() onCompleted()
http://csl.stanford.edu/~christos/pldi2010.Gt/meijer.duality.pdf
http://misgod.github.io/Slide-FRP-Android/ 第 8 ⾴

9. Observable & Observer
pushman.subscribe(new Action1<Integer>() {
@Override
public void call(Integer x) {
println("receive: " + x);
}
});
http://misgod.github.io/Slide-FRP-Android/ 第 9 ⾴

10. Observer pattern
http://misgod.github.io/Slide-FRP-Android/ 第 10 ⾴

11. Functional Reactive
http://misgod.github.io/Slide-FRP-Android/ 第 11 ⾴

12. Lambda Expression
http://misgod.github.io/Slide-FRP-Android/ 第 12 ⾴

13. Original
aObservable.filter(new Func1<Integer, Boolean>() {
public Boolean call(Integer n) {
return n % 2 == 0;
}
})
.map(new Func1<Integer, Integer>() {
public Integer call(Integer n) {
return n * n;
}
})
.subscribe(new Action1<Integer>() {
public void call(Integer n) {
System.out.println(n);
}
});
· WTF...
http://misgod.github.io/Slide-FRP-Android/ 第 13 ⾴

14. Java 8 lambda
aObservable.filter(n -> n % 2 == 0)
.map(n -> n * n)
.subscribe(System.out::println);
· but ... no java8 on Davilk(Android)
http://misgod.github.io/Slide-FRP-Android/ 第 14 ⾴

15. Retrolambda
Retrolambda lets you run Java 8 code with lambda expressions and
method references on Java 7 or lower.
Retrolambda
Gradle plugin
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https://github.com/orfjackal/- retrolambda
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- https://github.com/evant/gradle-retrolambda
http://misgod.github.io/Slide-FRP-Android/ 第 15 ⾴

16. Retrolambda
http://misgod.github.io/Slide-FRP-Android/ 第 16 ⾴

17. rx.Observable
http://misgod.github.io/Slide-FRP-Android/ 第 17 ⾴

18. Creating Observable - just
Observable<List<String>> ob = Observable.just(aList);
Observable<String> ob2 = Observable.just("Some String");
http://misgod.github.io/Slide-FRP-Android/ 第 18 ⾴

19. Creating Observable - from
List<String> aList = ...;
Observable<String> ob = Observable.from(aList);
http://misgod.github.io/Slide-FRP-Android/ 第 19 ⾴

20. Creating Observable - create
http://misgod.github.io/Slide-FRP-Android/ 第 20 ⾴

21. Creating Observable - create
ob = Observable.create(subscriber -> {
try {
for (String s : aList) {
if (subscriber.isUnsubscribed())
return;
subscriber.onNext(s);
}
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
});
http://misgod.github.io/Slide-FRP-Android/ 第 21 ⾴

22. Creating Observable ...
repeat( )
range( )
interval( )
timer( )
empty( )
error( )
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https://github.com/ReactiveX/RxJava/wiki/Creating-Observables
http://misgod.github.io/Slide-FRP-Android/ 第 22 ⾴

23. Transforming Observables - map
http://misgod.github.io/Slide-FRP-Android/ 第 23 ⾴

24. Transforming Observables - map
Observable.range(0, 5)
.map(x -> toBinaryString(x*x))
.subscribe(s -> println(s),
err -> err.printStackTrace(),
() -> println("done"));
0
1
100
1001
10000
done
http://misgod.github.io/Slide-FRP-Android/ 第 24 ⾴

25. Transforming Observables - flatmap
http://misgod.github.io/Slide-FRP-Android/ 第 25 ⾴

26. Transforming Observables - flatmap
Observable.range(1, 3)
.flatMap(x -> Observable.just(x).repeat(x))
.subscribe(System.out::println);
1
2
2
3
3
3
· Observable is a Monad
unit (return) ==> just
join (bind, >>=) ==> atmap
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http://misgod.github.io/Slide-FRP-Android/ 第 26 ⾴

27. Transforming Observables - concatmap
http://misgod.github.io/Slide-FRP-Android/ 第 27 ⾴

28. Filtering Observables
http://misgod.github.io/Slide-FRP-Android/ 第 28 ⾴

29. Filtering Observables
Observable.range(0, 10)
.filter(x - (x % 2) == 0)
.subscribe(System.out::println);
0
2
4
6
8
http://misgod.github.io/Slide-FRP-Android/ 第 29 ⾴

30. Filtering Observables
distinct( )
Grst( )
take( )
skip( )
elementAt( )
sample( )
more...
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https://github.com/ReactiveX/RxJava/wiki/Filtering-Observables
http://misgod.github.io/Slide-FRP-Android/ 第 30 ⾴

31. Aggregate Operators - reduce
http://misgod.github.io/Slide-FRP-Android/ 第 31 ⾴

32. Aggregate Operators - reduce
Observable.range(1, 10)
.reduce((a, b) - a*b)
.subscribe(System.out::println);
3628800
http://misgod.github.io/Slide-FRP-Android/ 第 32 ⾴

33. Aggregate Operators - concat
http://misgod.github.io/Slide-FRP-Android/ 第 33 ⾴

34. Combining Observables - merge
http://misgod.github.io/Slide-FRP-Android/ 第 34 ⾴

35. Combining Observables - merge
ObservableString lower = Observable.from(new String[]{a, b, c});
ObservableString upper = Observable.from(new String[]{A, B, C});
Observable.merge(lower,upper).subscribe(System.out::println);
/* Or */
lower.mergeWith(upper).subscribe(System.out::println);
a
b
A
c
B
C
http://misgod.github.io/Slide-FRP-Android/ 第 35 ⾴

36. Combining Observables - startWith
http://misgod.github.io/Slide-FRP-Android/ 第 36 ⾴

37. Combining Observables - startWith
ObservableString lower = Observable.from(new String[]{a, b, c});
ObservableString upper = Observable.from(new String[]{A, B, C});
lower.startWith(upper).subscribe(System.out::println);
A
B
C
a
b
c
http://misgod.github.io/Slide-FRP-Android/ 第 37 ⾴

38. Combining Observables - zip
http://misgod.github.io/Slide-FRP-Android/ 第 38 ⾴

39. Combining Observables - zip
ObservableString lower = Observable.from(new String[]{a, b, c});
ObservableString upper = Observable.from(new String[]{A, B, C});
Observable.zip(lower, upper, Pair::create)
.map(pair - pair.first +_ +pair.second)
.subscribe(System.out::println);
a_A
b_B
c_C
http://misgod.github.io/Slide-FRP-Android/ 第 39 ⾴

40. Error Handling
OnErrorResumeNext
OnErrorReturn
retry
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https://github.com/ReactiveX/RxJava/wiki/Error-Handling-Operators
http://misgod.github.io/Slide-FRP-Android/ 第 40 ⾴

41. Threading
observeOn
specify on which Scheduler a Subscriber should observe the Observable
subscribeOn
specify which Scheduler an Observable should use when its subscription is invoked
https://github.com/ReactiveX/RxJava/wiki/Scheduler
http://misgod.github.io/Slide-FRP-Android/ 第 41 ⾴

42. Subjects
A Subject = Subscriber + Observable
http://misgod.github.io/Slide-FRP-Android/ 第 42 ⾴

43. Subjects
PublishSubject
BehaviorSubject
AsyncSubject
ReplaySubject
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https://github.com/ReactiveX/RxJava/wiki/Subject
http://misgod.github.io/Slide-FRP-Android/ 第 43 ⾴

44. Subjects - How to use
Subscriber ----- Observable
PublishSubjectInteger subject = PublishSubject.create();
//Observable
subject.map(x - x*x)
.subscribe(o - println(o));
subject.map(x - x+1)
.subscribe(o - println(o));
//Subscriber
subject.onNext(11);
subject.onNext(11);
subject.onCompleted();
Masking a Subject as an Observable - aSubject.· asObservable()
http://misgod.github.io/Slide-FRP-Android/ 第 44 ⾴

45. Hot and Cold Observables
A “cold” Observable waits to emitting items until
observer subscribes , and so an observer can see the
whole sequenceg.
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A “hot” Observable may begins emitting items as soon
as it is created.
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http://misgod.github.io/Slide-FRP-Android/ 第 45 ⾴

46. RxJava on Android
http://misgod.github.io/Slide-FRP-Android/ 第 46 ⾴

47. About Android Development
Developing a robust app is painful
Developing a good UX app is painful
Thread, Executor, Handler, AsyncTask, Loader ...
RxJava can mitigate your pain
RetroGt supports methods with a return type of rx.Observable
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life cycle, async, event, state, threading, - error handling
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- interactive, realtime, smooth, animation
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@GET(/user/{id}/photo)
ObservablePhoto getUserPhoto(@Path(id) int id);
http://misgod.github.io/Slide-FRP-Android/ 第 47 ⾴

48. RxAndroid
Android speciGc bindings for RxJava.
https://github.com/- ReactiveX/RxAndroid
Scheduler on main UI thread or a given Android Handler thread.
AndroidSchedulers
HandlerThreadScheduler
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Reactive components for common Android use cases and UI widgets
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AndroidObservable
ViewObservable
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Don't forget to unsubscribe to avoid memory leak!
http://misgod.github.io/Slide-FRP-Android/ 第 48 ⾴

49. Thinking in Functional Reactive
http://misgod.github.io/Slide-FRP-Android/ 第 49 ⾴

50. Case 1 - Say Hello to Callback Hell
/* API */
void getFromServer(String key, Action1String callback);
void getFromDB(String key, Action1String callback);
/* Code */
btnClick.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
getFromDB(myid, new Action1String() {
public void call(String s) {
getFromServer(s, new Action1String() {
public void call(final String s) {
runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(context, s, LENGTH_LONG).show();
}
});
/* ... a lot of }) ... */
http://misgod.github.io/Slide-FRP-Android/ 第 50 ⾴

51. Case 1 - Say Hello to Callback Hell
Using Lambda expression
btnClick.setOnClickListener(view -
getFromDB(myid,
s - getFromServer(s,
x - runOnUiThread(
() - Toast.makeText(context, x, LENGTH_LONG).show()))));
· Shorter but not easy to read
http://misgod.github.io/Slide-FRP-Android/ 第 51 ⾴

52. Case 1 - Say Goodbye to Callback Hell
Using rx.Observable
/* API */
ObservableString getFromServer(String key);
ObservableString getFromDB(String key);
/* Code */
ViewObservable.clicks(btnClick)
.map(x - myid)
.observeOn(Schedulers.io())
.flatMap(this::getFromDB)
.flatMap(this::getFromServer)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(x - Toast.makeText(context, x, LENGTH_LONG).show());
http://misgod.github.io/Slide-FRP-Android/ 第 52 ⾴

53. Case 2 - All In One search
Requirements
A search engine includes google/yahoo/1. bing search results.
2. Should search diNerent engines in parallel
3. Retry 3 times when search fail
4. remove redundant url
ObservableSearchResult g = googleSearch.search(keyword).retry(3);
ObservableSearchResult b = bingSearch.search(keyword).retry(3);
ObservableSearchResult y = yahooSearch.search(keyword).retry(3);
Observable.merge(g, b, y)
.distinct(site - site.url)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(site - appendDataForUI() ,
err - errorhandle(err));
http://misgod.github.io/Slide-FRP-Android/ 第 53 ⾴

54. Case 3 - A simple EventBus
PublishSubjectObject subject = PublishSubject.create(); //Global Singleton
//...In Class A...
subject.filter(x - x instanceof DataUpdateAction)
.subscribe( x - ... doSomething ...);
//...In Class B...
subject.filter(x - x instanceof DeleteAction)
.subscribe( x - ... doSomething ...);
//...In Class C...
subject.filter(x - x instanceof RefreshAction)
.subscribe( x - ... doSomething ...);
subject.onNext(aDataUpdateAction);
subject.onNext(aDataUpdateAction;
subject.onNext(aRefreshAction);
http://misgod.github.io/Slide-FRP-Android/ 第 54 ⾴

55. Case 4 - Input Suggestion
private ObservableString getSuggestion(String prefix) { ... }
ObservableObservableListString o =
ViewObservable.text(aEditText)
.map(event - event.text.toString())
.filter(x - x.length() 1)
.observeOn(Schedulers.io())
.map(x - getSuggestion(x).toList());
Observable.switchOnNext(o)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(lst - showSuggestion(lst));
http://misgod.github.io/Slide-FRP-Android/ 第 55 ⾴

56. Conclusion
Functional Reactive makes async/state design 1. straightforward.
2. RxJava is not just a library.
3. The most important is Functional Reactive Thinking.
4. Try It in your next project!
http://misgod.github.io/Slide-FRP-Android/ 第 56 ⾴

57. http://misgod.github.io/Slide-FRP-Android/ 第 57 ⾴