This document provides an overview of RxAndroid and RxJava. It discusses key concepts like Observables that emit items, Subscribers that receive emitted items and complete/error notifications, and Operators like map that transform Observables. It shows how to create a simple Observable, subscribe to it, and use operators like map. It also demonstrates integrating Rx with Android by observing button clicks and updating UI, merging multiple Observables, and using scan to increment a counter and calculate a running sum from emitted values.

1. RxAndroid
Leo Y. Kim (@dalinaum)

2. Rx
The Reactive Extensions (Rx) is a library for
composing asynchronous and event-based
programs using observable sequences and
LINQ-style query operators.
https://msdn.microsoft.com/en-us/data/gg577609

3. RxJava
RxJava is a Java VM implementation of
Reactive Extensions: a library for composing
asynchronous and event-based programs by
using observable sequences.
Copyright 2013 Netflix, Inc.
(https://github.com/ReactiveX/RxJava)

4. RxAndroid

5. RxAndroid

6. build.gradle
dependencies {
...
compile 'io.reactivex:rxandroid:0.24.0'
}

7. Observable and Subscriber
River
Observable
onNext
onNext
onCompleted

8. onNext
An Observable calls this method whenever the
Observable emits an item. This method takes
as a parameter the item emitted by the
Observable.

9. onError
An Observable calls this method to indicate that
it has failed to generate the expected data or
has encountered some other error. This stops
the Observable and it will not make further calls
to onNext or onCompleted. The onError
method takes as its parameter an indication of
what caused the error.

10. onCompleted
An Observable calls this method after it has
called onNext for the final time, if it has not
encountered any errors.

11. 3 methods

12. Simple Observable
Observable<String> simpleObservable =
Observable.create(new Observable.OnSubscribe<String>() {
@Override
public void call(Subscriber<? super String> subscriber) {
subscriber.onNext("Hello RxAndroid !!");
subscriber.onCompleted();
}
});

13. Simple(?) Subscriber
simpleObservable
.subscribe(new Subscriber<String>() {
@Override
public void onCompleted() {
Log.d(TAG, "complete!");
}
(cont.)

14. Subscriber
@Override
public void onError(Throwable e) {
Log.e(TAG, "error: " + e.getMessage());
}
@Override
public void onNext(String text) {
((TextView) findViewById(R.id.textView)).setText(text);
}
});

15. Is it simple subsciber?
Not yet...

16. simpleObservable
.subscribe(new Action1<String>() {
@Override
public void call(String text) {
((TextView) findViewById(R.id.textView)).setText(text);
}
});
More simple subscriber #1

17. simpleObservable
.subscribe(new Action1<String>() {
...
}, new Action1<Throwable>() {
...
}, new Action0() {
...
});
More simple subscriber #2

18. simpleObservable
.subscribe(new Action1<String>() {
...
}, new Action1<Throwable>() {
...
});
More simple subscriber #3

19. Operator: Map

20. Operator: Map
.map(new Func1<Integer, Integer>() {
@Override
public Integer call(Integer value) {
return value * 10;
}
})

21. Operator: map
simpleObservable
.map(new Func1<String, String>() {
@Override
public String call(String text) {
return text.toUpperCase();
}
})
.subscribe(new Action1<String>() {
@Override
public void call(String text) {
((TextView) findViewById(R.id.textView)).setText(text);
}
});

22. Operator: map
simpleObservable
.map(new Func1<String, Integer>() {
@Override
public Integer call(String text) {
return text.length();
}
})
.subscribe(new Action1<Integer>() {
@Override
public void call(Integer length) {
((TextView) findViewById(R.id.textView)).setText("length: " + length);
}
});

23. More operators
http://reactivex.io/documentation/operators.html

24. Observer utilities
Observable<String> simpleObservable =
Observable.just("Hello RxAndroid");
see also: Observable.from (for collections)

25. Lambda
Observable<String> simpleObservable = Observable.just("Hello
Lambda!!");
simpleObservable
.map(text -> text.length())
.subscribe(length ->((TextView)findViewById(R.id.textView))
.setText("length: " + length));

26. What is that?
Java 8 Lambda

27. Lambda: stage 1
.map(new Func1<String, Integer>() {
@Override
public Integer call(String text) {
return text.length();
}
})

28. Lambda: stage 2
.map((String text) -> {
return text.length();
})

29. Lambda: stage 3
.map((text) -> {
return text.length();
})

30. Lambda: stage 4
.map(text -> {
return text.length();
})

31. Lambda: stage 5
.map(text ->
text.length()
)

33. Wait? Java 8!?!
Java 8 Lambda

34. Retrolambda
Java 8 Lambda

35. buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'me.tatarka:gradle-retrolambda:2.5.0'
}
}
apply plugin: 'com.android.application'
apply plugin: 'me.tatarka.retrolambda'
build.gradle

36. android {
...
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
…
}
build.gradle

37. RxAndroid: ViewObservable.clicks

38. ViewObservable.clicks
ViewObservable
.clicks(findViewById(R.id.button))
.map(event -> new Random().nextInt())
.subscribe(value -> {
TextView textView = (TextView) findViewB yId(R.id.textView);
textView.setText("number: " + value.toString());
}, throwable -> {
Log.e(TAG, "Error: " + throwable.getMessage());
throwable.printStackTrace();
});

39. Observable<Event>
ViewObservable
.clicks(findViewById(R.id.button))
.map(event -> new Random().nextInt())
.subscribe(value -> {
TextView textView = (TextView) findViewById(R.id.textView);
textView.setText("number: " + value.toString());
}, throwable -> {
Log.e(TAG, "Error: " + throwable.getMessage());
throwable.printStackTrace();
});

40. Map: Event -> Integer
ViewObservable
.clicks(findViewById(R.id.button))
.map(event -> new Random().nextInt())
.subscribe(value -> {
TextView textView = (TextView) findViewById(R.id.textView);
textView.setText("number: " + value.toString());
}, throwable -> {
Log.e(TAG, "Error: " + throwable.getMessage());
throwable.printStackTrace();
});

41. Subscriber
ViewObservable
.clicks(findViewById(R.id.button))
.map(event -> new Random().nextInt())
.subscribe(value -> {
TextView textView = (TextView) findViewById(R.id.textView);
textView.setText("number: " + value.toString());
}, throwable -> {
Log.e(TAG, "Error: " + throwable.getMessage());
throwable.printStackTrace();
});

42. Observable.merge

43. Merge

44. Observable.merge
Observable<String> lefts = ViewObservable.clicks(findViewById(R.id.leftButton))
.map(event -> "left");
Observable<String> rights = ViewObservable.clicks(findViewById(R.id.
rightButton))
.map(event -> "right");
Observable<String> together = Observable.merge(lefts, rights);
together.subscribe(text -> ((TextView) findViewById(R.id.textView)).setText(text));
together.map(text -> text.toUpperCase())
.subscribe(text -> Toast.makeText(this, text, Toast.LENGTH_SHORT).show());

45. 2 Observables
Observable<String> lefts = ViewObservable.clicks(findViewById(R.id.leftButton))
.map(event -> "left");
Observable<String> rights = ViewObservable.clicks(findViewById(R.id.
rightButton))
.map(event -> "right");
Observable<String> together = Observable.merge(lefts, rights);
together.subscribe(text -> ((TextView) findViewById(R.id.textView)).setText(text));
together.map(text -> text.toUpperCase())
.subscribe(text -> Toast.makeText(this, text, Toast.LENGTH_SHORT).show());

46. Observable.merge
Observable<String> lefts = ViewObservable.clicks(findViewById(R.id.leftButton))
.map(event -> "left");
Observable<String> rights = ViewObservable.clicks(findViewById(R.id.
rightButton))
.map(event -> "right");
Observable<String> together = Observable.merge(lefts, rights);
together.subscribe(text -> ((TextView) findViewById(R.id.textView)).setText(text));
together.map(text -> text.toUpperCase())
.subscribe(text -> Toast.makeText(this, text, Toast.LENGTH_SHORT).show());

47. 2 Subscriber
Observable<String> lefts = ViewObservable.clicks(findViewById(R.id.leftButton))
.map(event -> "left");
Observable<String> rights = ViewObservable.clicks(findViewById(R.id.
rightButton))
.map(event -> "right");
Observable<String> together = Observable.merge(lefts, rights);
together.subscribe(text -> ((TextView) findViewById(R.id.textView)).setText(text));
together.map(text -> text.toUpperCase())
.subscribe(text -> Toast.makeText(this, text, Toast.LENGTH_SHORT).show());

48. Operator: scan

50. Operator: scan
Observable<Integer> minuses = ViewObservable.clicks(findViewById(R.id.minusButton))
.map(event -> -1);
Observable<Integer> pluses = ViewObservable.clicks(findViewById(R.id.plusButton))
.map(event -> 1);
Observable<Integer> together = Observable.merge(minuses, pluses);
together.scan(0, (sum, number) -> sum + 1)
.subscribe(count ->
((TextView) findViewById(R.id.count)).setText(count.toString()));
together.scan(0, (sum, number) -> sum + number)
.subscribe(number ->
((TextView) findViewById(R.id.number)).setText(number.toString()));

51. 2 Observables (+map)
Observable<Integer> minuses = ViewObservable.clicks(findViewById(R.id.minusButton))
.map(event -> -1);
Observable<Integer> pluses = ViewObservable.clicks(findViewById(R.id.plusButton))
.map(event -> 1);
Observable<Integer> together = Observable.merge(minuses, pluses);
together.scan(0, (sum, number) -> sum + 1)
.subscribe(count ->
((TextView) findViewById(R.id.count)).setText(count.toString()));
together.scan(0, (sum, number) -> sum + number)
.subscribe(number ->
((TextView) findViewById(R.id.number)).setText(number.toString()));

52. Merge
Observable<Integer> minuses = ViewObservable.clicks(findViewById(R.id.minusButton))
.map(event -> -1);
Observable<Integer> pluses = ViewObservable.clicks(findViewById(R.id.plusButton))
.map(event -> 1);
Observable<Integer> together = Observable.merge(minuses, pluses);
together.scan(0, (sum, number) -> sum + 1)
.subscribe(count ->
((TextView) findViewById(R.id.count)).setText(count.toString()));
together.scan(0, (sum, number) -> sum + number)
.subscribe(number ->
((TextView) findViewById(R.id.number)).setText(number.toString()));

53. 1st scan + subscriber: counter
Observable<Integer> minuses = ViewObservable.clicks(findViewById(R.id.minusButton))
.map(event -> -1);
Observable<Integer> pluses = ViewObservable.clicks(findViewById(R.id.plusButton))
.map(event -> 1);
Observable<Integer> together = Observable.merge(minuses, pluses);
together.scan(0, (sum, number) -> sum + 1)
.subscribe(count ->
((TextView) findViewById(R.id.count)).setText(count.toString()));
together.scan(0, (sum, number) -> sum + number)
.subscribe(number ->
((TextView) findViewById(R.id.number)).setText(number.toString()));

54. 2nd scan + subscriber: sum
Observable<Integer> minuses = ViewObservable.clicks(findViewById(R.id.minusButton))
.map(event -> -1);
Observable<Integer> pluses = ViewObservable.clicks(findViewById(R.id.plusButton))
.map(event -> 1);
Observable<Integer> together = Observable.merge(minuses, pluses);
together.scan(0, (sum, number) -> sum + 1)
.subscribe(count ->
((TextView) findViewById(R.id.count)).setText(count.toString()));
together.scan(0, (sum, number) -> sum + number)
.subscribe(number ->
((TextView) findViewById(R.id.number)).setText(number.toString()));

55. Scheduler

56. Scheduler
Observable.from("one", "two", "three", "four", "five")
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(/* an Observer */);

57. Observable runs on “newThread”
Observable.from("one", "two", "three", "four", "five")
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(/* an Observer */);

58. Subscriber runs on “mainThread”
Observable.from("one", "two", "three", "four", "five")
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(/* an Observer */);
Notice:
Subscriber doesn’t run on mainThread immediately.

59. Bound
new Thread(() -> {
final Handler handler = new Handler();
Observable.from("one", "two", "three", "four", "five")
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.handlerThread(handler))
.subscribe(/* an Observer */)
}, "custom-thread-1").start();

60. Bound to this thread
new Thread(() -> {
final Handler handler = new Handler();
Observable.from("one", "two", "three", "four", "five")
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.handlerThread(handler))
.subscribe(/* an Observer */)
}, "custom-thread-1").start();

61. Varieties of Scheduler (RxJava)
● Schedulers.computation( )
● Schedulers.from(executor)
● Schedulers.immediate( )
● Schedulers.io( )
● Schedulers.newThread( )
● Schedulers.trampoline( )

62. Varieties of Scheduler (RxAndroid)
● AndroidSchedulers.mainThread()
● AndroidSchedulers.handlerThread(handler)

63. Use Schedulers without Observable
worker =
Schedulers.newThread().createWorker();
worker.schedule(() -> {
yourWork();
});

64. Unsubscirbe Subscription
Subscription s = Observable.from("one", "two",
"three", "four", "five").subscribe(/* Observer */)
s.unsubscribe()

65. Unsubscirbe CompositeSubscription
private void doSomething() {
mCompositeSubscription.add(
s.subscirbe(/* observer*/);
}
@Override
protected void onDestroy() {
super.onDestroy();
mCompositeSubscription.unsubscribe();
}

66. Unsubscirbe Subscription
@Override
protected void onDestroy() {
super.onDestroy();
s.unsubscribe();
}

67. Recursive Schedulers
worker = Schedulers.newThread().createWorker();
worker.schedule(() {
yourWork();
worker.schedule(this);
});
// It will stop your worker
worker.unsubscribe();

68. Retrofit with RxAndroid

69. Retrofit without RxAndroid
@GET(“/user/{id}”)
void getUser(
@path(“id”) long id,
Callback<User> callback);

70. Retrofit with RxAndroid
@GET(“/user/{id}”)
Observable<User> getUser(
@path(“id”) long id);

71. You can combie Retrofit’s Observables
Observable.zip(
service.getUserPhoto(id),
service.getPhotoMetadata(id),
(photo, metadata) -> createPhotoWithData(photo,
metadata))
.subscribe(photoWithData ->
showPhoto(photoWithData));

72. Battery with RxAndroid
https://github.com/spoqa/battery

73. Battery with RxAndroid
@RpcObject(uri="http://ip.jsontest.com/")
public class JsonTest {
@Response public String ip;
}
Observable<JsonTest> jsonTestObservable =
Rpc.invokeRx(new AndroidExecutionContext(this), jsonTest);
jsonTestObservable.subscribe(jsonText -> {
Log.d("MAIN", jsonTest.ip);
});

74. Subject

75. Subject
A Subject is a sort of bridge or proxy
that is available in some
implementations of ReactiveX that
acts both as an observer and as an
Observable.

77. PublishSubject
PublishSubject publishSubject<View> =
PublishSubject.create();
view.setOnClickListener(view ->
publishSubject.onNext(view));
Observable<View> observable =
publishSubject.asObservable();

81. Use ReplaySubject for caching
ReplaySubject<ImageSearchResult> mSubject =
ReplaySubject.create();
mSubject = ReplaySubject.create();
mPageNumber = 1;
mApi.searchImage(
"json", API_KEY, query, ITEM_COUNT, mPageNumber)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(mSubject::onNext);

82. Q&A

83. See also
https://github.com/GDG-Korea/HelloRx
https://github.com/hl5pma/RxExample