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(){ @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 getStrings() { return Observable.create(new Observable.OnSubscribe() { @Override public void call(Subscriber 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 myObservable = Observable.just("Hello, world!"); Action1 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 

Operators 

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 

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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 

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

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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 compose : Observable -> Observable #ProTips 

Retrofit Integration @GET("mobile_detail_calc_halte_trans.php") Observable> 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 imageObservable = Observable.create(observer -> { Bitmap bm = downloadBitmap(); return bm; }); imageObservable.subscribe(image -> loadToImageView(image)); // blocking the UI thread imageObservable .subscribeOn(Schedulers.newThread()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(image -> loadToImageView(image)); // non blocking but also execute loadToImageView on UI Thread 

More Examples public Observable> getAreas() { Observable> network = mApiService.getArea() .observeOn(AndroidSchedulers.mainThread()) .doOnNext(areas -> saveAreas(areas)); Observable> 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) .observeOn(AndroidSchedulers.mainThread()) .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 

Questions?