Introduction to rx java for android

Introduction to RxJava for
Android
Esa Firman

What is RxJava?
RxJava is a Java VM implementation of ReactiveX (Reactive
Extensions): a library for composing asynchronous and
event-based programs by using observable sequences
See also: 2 minutes introduction to Rx
https://medium.com/@andrestaltz/2-minute-introduction-to-rx-24c8ca793877#.rwup8ee0s

The Problem
How to deal with execution context ?

Threads
Handler handler = new Handler(Looper.getMainLooper());
new Thread(){
@Override
public void run() {
final String result = doHeavyTask();
handler.post(new Runnable() { // or runUIThread on Activity
@Override
public void run() {
showResult(result);
}
});
}
}.start();

Threads
Pros:
- Simple
Cons:
- Hard way to deliver results in UI thread
- Pyramid of Doom

AsyncTask
new AsyncTask<Void, Integer, String>(){
@Override
protected String doInBackground(Void... params) {
return doHeavyTask();
}
@Override
protected void onPostExecute(String s) {
showResult(s);
}
}.execute();

AsyncTask
Pros:
- Deal with main thread
Cons:
- Hard way to handling error
- Not bound to activity/fragment lifecycle
- Not composable
- Nested AsyncTask
- “Antek Async”

Why Rx?
- Because multithreading is hard
- Execution context
- Powerful operators
- Composable
- No Callback Hell
- Etc ...

The Basic
The basic building blocks of reactive code are Observables
and Subscribers. An Observable emits items; a Subscriber
consumes those items.
The smallest building block is actually an Observer, but in practice you are most often using Subscriber because that's how
you hook up to Observables.

The Basic
Observables often don't start emitting items until someone
explicitly subscribes to them

Enough talk, let’s see some code ...

Hello World
public Observable<String> getStrings() {
return Observable.create(new Observable.OnSubscribe<String>() {
@Override
public void call(Subscriber<? super String> subscriber) {
try {
subscriber.onNext("Hello, World");
subscriber.onCompleted();
} catch (Exception ex) {
subscriber.onError(ex);
}
}
});
}

Hello World
getStrings().subscribe(new Subscriber(){
@Override
public void onCompleted() {
// no - op
}
@Override
public void onError(Throwable e) {
e.printStackTrace();
}
@Override
public void onNext(String s) {
System.out.println(s);
}
};

Observable<String> myObservable = Observable.just("Hello, world!");
Action1<String> onNextAction = new Action1<>() {
@Override
public void call(String s) {
System.out.println(s);
}
};
myObservable.subscribe(onNextAction);
// Outputs "Hello, world!"
Simpler Code

Simplest* Code - Using Lambda
Observable.just("Hello, World").subscribe(System.out::println);
*AFAIK

Observable Creation
Observable.create(Observable.onSubscribe)
from( ) — convert an Iterable or a Future or single value into an Observable
repeat( ) — create an Observable that emits a particular item or sequence of items repeatedly
timer( ) — create an Observable that emits a single item after a given delay
empty( ) — create an Observable that emits nothing and then completes
error( ) — create an Observable that emits nothing and then signals an error
never( ) — create an Observable that emits nothing at all

Filtering Operators
- filter( ) — filter items emitted by an Observable
- takeLast( ) — only emit the last n items emitted by an Observable
- takeLastBuffer( ) — emit the last n items emitted by an Observable, as a single list item
- skip( ) — ignore the first n items emitted by an Observable
- take( ) — emit only the first n items emitted by an Observable
- first( ) — emit only the first item emitted by an Observable, or the first item that meets some condition
- elementAt( ) — emit item n emitted by the source Observable
- timeout( ) — emit items from a source Observable, but issue an exception if no item is emitted in a
specified timespan
- distinct( ) — suppress duplicate items emitted by the source Observable

Introduction to rx java for android

Filter
Observable.just("Esa", "Ganteng", "Jelek")
.filter(s -> !s.equalsIgnoreCase("jelek"))
.buffer(2)
.subscribe(strings -> {
print(strings.get(0) + “ “ + strings.get(1));
});
// print Esa Ganteng

Transformation Operators
- map( ) — transform the items emitted by an Observable by applying a function to each of them
- flatMap( ) — transform the items emitted by an Observable into Observables, then flatten this into a
single Observable
- scan( ) — apply a function to each item emitted by an Observable, sequentially, and emit each
successive value
- groupBy( ) and groupByUntil( ) — divide an Observable into a set of Observables that emit groups of
items from the original Observable, organized by key
- buffer( ) — periodically gather items from an Observable into bundles and emit these bundles rather
than emitting the items one at a time
- window( ) — periodically subdivide items from an Observable into Observable windows and emit these
windows rather than emitting the items one at a time

Map
Observable.from(Arrays.asList("Esa", "Esa", "Esa"))
.map(s -> s + " ganteng")
.subscribe(System.out::println);
// print Esa ganteng 3 times

FlatMap
Observable.just( Arrays.asList("Tiramisu", "Black Forest", "Black Mamba"))
.flatMap(Observable::from)
.map(String::length)
.subscribe(System.out::print);
// print 8,11,12

Confused?
Getting map/flatMap/compose mixed up? Think types:
map : T -> R
flatMap : T -> Observable<R>
compose : Observable<T> -> Observable<R>
#ProTips

Retrofit Integration
@GET("mobile_detail_calc_halte_trans.php")
Observable<List<HalteDetail>>
getHalteDetails(@Query("coridor") String coridor);
mApiService.getHalteDetails(halte.getCoridor())
.observeOn(AndroidSchedulers.mainThread())
.doOnTerminate(this::resetUILoading)
.subscribe(halteDetails -> {
if (halteDetails != null) {
setMarker(halteDetails);
}
});

More Examples
mApiService.getCommentList()
.compose(bindToLifecycle())
.compose(applyApiCall())
.doOnTerminate(this::stopLoading)
.subscribe(comments -> {
if (comments != null)
mCommentAdapter.pushData(comments);
});

More Samples
Observable<Bitmap> imageObservable = Observable.create(observer -> {
Bitmap bm = downloadBitmap();
return bm;
});
imageObservable.subscribe(image -> loadToImageView(image));
// blocking the UI thread
imageObservable
.subscribeOn(Schedulers.newThread())
.subscribe(image -> loadToImageView(image));
// non blocking but also execute loadToImageView on UI Thread

More Examples
public Observable<List<Area>> getAreas() {
Observable<List<Area>> network = mApiService.getArea()
.doOnNext(areas -> saveAreas(areas));
Observable<List<Area>> cache = getAreasFromLocal();
return Observable.concat(cache, network).first(areas -> areas != null);
}

More Examples (Again)
public void onLocationChanged(Location location) {
onLocationChanged.onNext(location);
}
mGmsLocationManager.onLocationChanged
.throttleLast(10, TimeUnit.SECONDS)
.subscribe(location -> {
mPrensenter.updateMyLocation(location);
});

FAQ
1. Should we still use Thread and AsyncTask?
2. Where to start?

Third Party Implementation
- Android ReactiveLocation https://github.com/mcharmas/Android-
ReactiveLocation
- RxPermissions
https://github.com/tbruyelle/RxPermissions
- RxBinding
https://github.com/JakeWharton/RxBinding
- SQLBrite
https://github.com/square/sqlbrite
- RxLifeCycle
https://github.com/trello/RxLifecycle

Links
- http://slides.com/yaroslavheriatovych/frponandroid
- https://github.com/Netflix/RxJava/
- https://github.com/orfjackal/retrolambda
- https://github.com/evant/gradle-retrolambda
- http://cr.openjdk.java.net/~briangoetz/lambda/lambda-translation.html
- https://github.com/Netflix/RxJava/wiki

Introduction to rx java for android

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