Landi Migration Workshop Traini… · One more example to control thread - Traditionally Landi APOS...

RxJava Introduction

JUNE 2017

FUZHOU, CHINA

Why RxJava

Show all png image to UI - Traditional

Landi APOS A8 training – June 2017

new Thread() {@Overridepublic void run() {

super.run();for (File folder : folders) {

File[] files = folder.listFiles();for (File file : files) {

if (file.getName().endsWith(".png")) {final Bitmap bitmap = getBitmapFromFile(file);getActivity().runOnUiThread(new Runnable() {

@Overridepublic void run() {

imageCollectorView.addImage(bitmap);}

}}.start();

Logic Nesting

Show all png image to UI - RxJava

Observable.fromArray(folders)

.flatMap(file -> Observable.fromArray(file.listFiles()))

.filter(file -> file.getName().endsWith(".png"))

.map(file -> getBitmapFromFile(file))

.subscribeOn(Schedulers.io())

.observeOn(AndroidSchedulers.mainThread())

.subscribe((Consumer<Bitmap>) bitmap -> imageCollectorView.addImage(bitmap));

Another example to avoid callback hell - Callback

private void downloadParameters() {EmvParameterDownloader emvParameterDownloader = new EmvParameterDownloader(context);

new TerminalParameterDownloader().download(new Runnable(){@Overridepublic void run() {

emvParameterDownloader.downloadICParameters(new Runnable(){@Overridepublic void run() {

emvParameterDownloader.downloadPublicKeys();}

Callback Hell

Another example to avoid callback hell - RxJava

private Completable downloadParameters() {EmvParameterDownloader emvParameterDownloader = new EmvParameterDownloader(context);new TerminalParameterDownloader(context).download())

.andThen(emvParameterDownloader.downloadICParameters())

.andThen(emvParameterDownloader.downloadPublicKeys());}

One more example to control thread - Traditionally

private void login() {// find userreturn findUser(name, password, new Runnable(){

updateLastLoginUser(user);

runOnUiThread(new Runnable() {@Overridepublic void run() {

user -> handleLogonUser(user);}

One more example to control thread - RxJava

private Completable login() {// find userreturn findUser(name, password)

// update last login user.doOnSuccess(user -> updateLastLoginUser(user))

.flatMapCompletable(user -> handleLogonUser(user));}

One more example to handle error - Traditional

private Handler handler = new Handler(Looper.getMainLooper()){@Overridepublic void handleMessage(Message msg) {

if(msg.what == DOWNLOAD_IMG){Exception data = (Exception)msg.obj;// show exception

public void signIn() {new Thread(new Runnable() {

try {// business logic

}catch (Exception e){Message message = Message.obtain();message.obj = e;message.what = ERROR;

handler.sendMessage(message);}}

}).start();}

One more example to handle error - RxJava

Landi APOS A8 training – August 2017

public void signIn() {new SignIn(context).signIn()

.subscribe(new DisposableCompletableObserver() {@Overridepublic void onComplete() {

@Overridepublic void onError(@NonNull Throwable e) {

// show error}

Process

STEP 04STEP 02

STEP 03 STEP 05STEP 01

How we use in Arke ProjectIntroduce ReactiveX and

RxJava

RxJava Topics

Observable/Observer/Schedue

rler/Error Handling

Learning Path Lambda Expression

ReactiveXAn asynchronous and event-based programs solution.

Functional Less is more Async error handling Concurrency made easy

CROSS-PLATFORM

Java: RxJava

JavaScript: RxJS

C#: Rx.NET

C#(Unity): UniRx

Scala: RxScala

Clojure: RxClojure

C++: RxCpp

Lua: RxLua

Ruby: Rx.rb

Python: RxPY

Go: RxGo

Groovy: RxGroovy

JRuby: RxJRuby

Kotlin: RxKotlin

Swift: RxSwift

PHP: RxPHP

Elixir: reaxive

Dart: RxDart

RxNetty RxAndroid RxCocoa

RxJava and RxAndroid

AsyncTask

AsyncTaskLoaderRxJavaThread and Handler

Introduction to RxJava for Android Developers

Intro to RxJavaWhat's different in 2.0

Why and how to replace Thread and AsyncTask

Learning Path & Resouces

Examples

- training / RxJava2-Android-Samples

- kaushikgopal/RxJava-Android-

Samples

- How we use in Arke Project.

Pratice and Google

- Practice in Project

- Google and Thinking

- ReactiveX Official Site

- ReactiveX GitHub

- RxJava GitHub

- RxJava Category in my Blog

- Exploring RxJava 2 for Android

Jake Wharton

- Intro to RxJava for Android

- Intro to RxJava

Guide by Arke Team

Reactive Programming with RxJava

Official Site

Shut up, show me the code

Observable.fromArray(folders)

.flatMap(file -> Observable.fromArray(file.listFiles()))

.filter(file -> file.getName().endsWith(".png"))

.map(file -> getBitmapFromFile(file))

.subscribeOn(Schedulers.io())

.subscribe((Consumer<Bitmap>) bitmap -> imageCollectorView.addImage(bitmap));

Primer on RxJava

// include RxJava librarycompile 'io.reactivex.rxjava2:rxjava:2.0.6'

// include RxAndroid librarycompile 'io.reactivex.rxjava2:rxandroid:2.0.1'

Key Concepts

S c h e d u l e r

O b s e r v a b l eO b s e r v e r

/ S u b s c r i b e r

O p e r a t o r

Concepts

Observable

- How to create

- How to subscribe

- How to unsubscribe

- Subject

Observable event types

- OnNext

- onComplete

- onError

OnNext* (OnComplet | OnError)?

How to emit events

Observable<Integer> ints = Observable.create(new ObservableOnSubscribe(){

@Overridepublic void subscribe(ObservableEmitter emitter) throws Exception {

emitter.onNext(5);emitter.onNext(6);emitter.onNext(7);emitter.onComplet();

Hot and Cold Observables

No subscriber, no events emit

Observable

Event no subscriber, always emit

events

Hot Observable

Reactive Types

Single

Completable

Flowable

Observable

CompletableObserverExampleActivity.javaSingleObserverExampleActivity.java

MaybeObserverExampleActivity.java

FlowableExampleActivity.java

Backpressure

Backpressure No Backpressure

Flowable Observable

Single

Completable

When to use Flowable When to use Observable

10k+ events > 1k events

pull-based push-based

Reactive Types Transformation

// Completable to FlowableCompletable.complete().toFlowable();

// Completable to MaybeCompletable.complete().toMaybe();

// Completable to ObservableCompletable.complete().toObservable();

// Completable to SingleCompletable.complete().toSingleDefault(1);

Create Observable

// convert an object or a set of objects into an Observable that emits that or those objectsObservable.just("one");Observable.just(1, 2);

// convert some other object or data structure into an ObservableObservable.fromArray(1, 2, 3);Observable.fromCallable();Observable.fromFuture();

// create an Observable that emits a sequence of integers spaced by a particular time intervalObservable.interval(1, TimeUnit.SECONDS);

// create an Observable that emits a particular range of sequential integersObservable.range(1, 10);

// create Observables that have very precise and limited behaviorObservable.empty();Observable.error();Observable.never();

Create Observable with Observable.create()

Observable<Integer> ints = Observable.create(new ObservableOnSubscribe(){

@Overridepublic void subscribe(ObservableEmitter emitter) throws Exception {

emitter.onNext(5);emitter.onNext(6);emitter.onNext(7);emitter.onComplet();

Maybe, Completable, Single, Flowable Creation

// create Completables that have very precise and limited behavior Completable.complete();Completable.error();Completable.never();Completable.timer();

// convert some other object or data structure into an ObservableCompletable.fromAction();Completable.fromCallable();Completable.fromFuture();Completable.fromRunnable();

// convert some other reactive types into an ObservableCompletable.fromObservable();Completable.fromPublisher();Completable.fromSingle();

Completable.create();

Subscribing Observable

// Subscribe with ObserverObservable.just("one").subscribe(new Observer<String>() {

@Overridepublic void onSubscribe(@NonNull Disposable d) {

Log.d(TAG, "Subscribed");}

@Overridepublic void onNext(@NonNull String s) {

Log.d(TAG, "Got events " + s);}

@Overridepublic void onError(@NonNull Throwable e) {

Log.d(TAG, "Error happened");}

@Overridepublic void onComplete() {

Log.d(TAG, "Completed");}

Simple Subscribing Observable

Observable.just("one").subscribe(new Consumer<String>() {@Overridepublic void accept(@NonNull String s) throws Exception {

Log.d(TAG, s);}

OnNext

Observable.just("one").subscribe(new Consumer<String>() {@Overridepublic void accept(@NonNull String s) throws Exception {

Log.d(TAG, s);}

}, new Consumer<Throwable>() {@Overridepublic void accept(@NonNull Throwable throwable) throws Exception {

Log.e(TAG, throwable.getMessage());}

onNext

onError

Disposable subscribe(Consumer<? super T> onNext, Consumer<? super Throwable> onError,

Action onComplete, Consumer<? super Disposable> onSubscribe)Full

Types of Observer

Unsubscribing from Observable

Observable.just("one", "two").subscribe(new DisposableObserver<String>() {@Overridepublic void onNext(String s) {

if(s.equals("two")){dispose();

@Overridepublic void onError(Throwable e) {

dispose();}

Subject

- AsyncSubject

- BehaviorSubject

- PublishSubject

- ReplaySubject

AsyncSubject

AsyncSubjectExampleActivity.java

BehaviorSubject

BehaviorSubjectExampleActivity.java

PublishSubject

PublishSubjectExampleActivity.java

ReplaySubject

Lambda

Expression

Use Retrolambda

No Step 3

Download jdk8 and set it as

your default.

Project build.gradle

compileOptions {targetCompatibility 1.8sourceCompatibility 1.8

In project build.gradle:

Gradle

In module build.gradle:

buildscript {dependencies {

classpath 'me.tatarka:gradle-retrolambda:3.6.0'

apply plugin: 'com.android.application' apply plugin: 'me.tatarka.retrolambda'

Syntax of Lambda Expressions

(a, b) -> {System.out.println("Performing add operation...");return a+b;

1. Input parameter

2. Arrow token

3. Code block

a -> a + 1;

Lambda Expressions used in RxJava

getObservable().map(new Function<List<ApiUser>, List<User>>() {

@Overridepublic List<User> apply(List<ApiUser> apiUsers) throws Exception {

return Utils.convertApiUserListToUserList(apiUsers);}

Do an exercise: MapExampleActivity.java

Anonymous function demo:

getObservable().map(apiUsers -> Utils.convertApiUserListToUserList(apiUsers));

Replace with Lambda Expression:

Operator

Marble Diagrams

Operators Categories

CATEGORY

06 A toolbox of useful Operators for

working with Observables.

Utility OperatorsCATEGORY

04 Work with multiple source

Observables to create a single

Observable.

CombiningCATEGORY

05 Help to recover from error

notifications from an Observable.

Error Handling Operators

CATEGORY

03 Selectively emit items from a

source Observable.

FilteringCATEGORY

02 Frequently, your initial font choice

is taken out of your hands

TransformingCATEGORY

01 Originate new Observables

Creating

CATEGORY

09 Specialty Observables that have more

precisely-controlled subscription

dynamics.

ConnectableCATEGORY

07 Evaluate one or more

Observables or items emitted by

Observables.

CATEGORY

08 Operate on the entire sequence

of items emitted by an

Observable

Mathematical and AggregateConditional

ReactiveX - Operators Which Operator do I use?

Filtering Operators

- filter

- distinct

- distinctUtilChanged

Filtering

filter example

Observable.just(1, 2, 3, 4, 5).filter(item -> item < 4)).subscribe(new DisposableObserver<Integer>() {

@Overridepublic void onNext(Integer item) {

System.out.println("Next: " + item);}

@Overridepublic void onError(Throwable error) {

System.err.println("Error: " + error.getMessage());}

System.out.println("Sequence complete.");}

Dropping Duplicates Using distinct() and distinctUntilChanged()

Observable.just(1, 2, 1, 1, 2, 3).distinct(); // [1, 2, 3]

Observable.just(1, 2, 1, 1, 2, 3).distinctUntilChanged(); // [1, 2, 1, 2, 3]

Utility Operators

- delay

Postponing Events Using the delay()

just(x, y, z).delay(1, TimeUnit.SECONDS);

Transforming Operators

- flatMap

- concatMap

map() Operator

Map example

MapExampleActivity.java

Observable<Status> tweets = //...Observable<Date> dates = tweets.map(status ->

status.getCreatedAt());

Observable<Instant> instants = tweets.map(Status::getCreatedAt).map((Date d) -> d.toInstant());

Wrapping Up Using flatMap()

Flatmap example - Flatten students to course list

List<Student> students = new ArrayList<Student>();// students.add...

Observable.from(students).flatMap(student -> Observable.from(student.getCoursesList());).subscribe(course -> Log.i(TAG, course.getName()));

Flatmap exercise

Observable<Integer> oneToEight = Observable.range(1, 8);

Observable<String> ranks = oneToEight.map(Object::toString);

Observable<String> files = oneToEight.map(x -> 'a' + x - 1).map(ascii -> (char)ascii.intValue()).map(ch -> Character.toString(ch));

Observable<String> squares = files.flatMap(file -> ranks.map(rank -> file + rank));

Order of Events After flatMap()

just(10L, 1L).flatMap(x ->just(x).delay(x, TimeUnit.SECONDS)).subscribe(System.out::println);

Another flatMap exercise

Observable<String> loadRecordsFor(DayOfWeek dow) {switch(dow) {

case SUNDAY:return Observable

.interval(90, MILLISECONDS)

.take(5)

.map(i -> "Sun-" + i);case MONDAY:

return Observable.interval(65, MILLISECONDS).take(5).map(i -> "Mon-" + i);

//...}

Observable.just(DayOfWeek.SUNDAY, DayOfWeek.MONDAY).flatMap(this::loadRecordsFor);

Preserving Order Using concatMap()

Observable

.just(DayOfWeek.SUNDAY, DayOfWeek.MONDAY)

.concatMap(this::loadRecordsFor);

Sun-0, Sun-1, Sun-2, Sun-3, Sun-4, Mon-0, Mon-1,

Mon-2, Mon-3, Mon-4

Observable

.just(DayOfWeek.SUNDAY, DayOfWeek.MONDAY)

.flatMap(this::loadRecordsFor);

Mon-0, Sun-0, Mon-1, Sun-1, Mon-2, Mon-3, Sun-2,

Mon-4, Sun-3, Sun-4

Combining Operators

- combineLatest

- concat

- merge

Pairwise Composing Using zip()

zip() example

Observable<Long> red = Observable.interval(10, TimeUnit.MILLISECONDS);Observable<Long> green = Observable.interval(10, TimeUnit.MILLISECONDS);

Observable.zip(red.timestamp(),green.timestamp(),(r, g) -> r.getTimestampMillis() - g.getTimestampMillis()

).forEach(System.out::println);

ZipExampleActivity.java

Observable<Long> red = Observable.interval(10, TimeUnit. SECONDS);Observable<Long> green = Observable.interval(10, TimeUnit.MILLISECONDS);

Observable.zip(red.timestamp(),green.timestamp(),(r, g) -> r.getTimestampMillis() - g.getTimestampMillis()

When Streams Are Not Synchronized with One Another

combineLatest example

FormValidationCombineLatestFragment.java

Observable.combineLatest(interval(170, MILLISECONDS).map(x -> "S" + x),interval(100, MILLISECONDS).map(x -> "F" + x),(s, f) -> f + ":" + s

Ways of Combining Streams: concat(), merge()

MergeExampleActivity.java, ConcatExampleActivity.java

Merge & Concat Example

final Observable<String> sundayObservable = Observable.interval(90, MILLISECONDS).take(5).map(i -> "Sun-" + i);

final Observable<String> mObservable = Observable.interval(65, MILLISECONDS).take(5).map(i -> "Mon-" + i);

Observable.merge(sundayObservable, mondayObservable); Observable.concat(sundayObservable, mondayObservable);

Mon-0, Sun-0, Mon-1, Sun-1, Mon-2, Mon-3, Sun-2, Mon-4, Sun-3, Sun-4

Sun-0, Sun-1, Sun-2, Sun-3, Sun-4, Mon-0, Mon-1, Mon-2, Mon-3, Mon-4

Conditional Operators

all, exists, contain

Observable<Integer>numbers = Observable.range(1, 5);

numbers.all(x -> x != 4); // [false]numbers.exists(x -> x == 4); // [true]numbers.contains(4); // [true]

Schedulers

- observeOn

- subscribeOn

A simple Observable – A simple data source

private Observable<String> simple() {return Observable.create(emitter -> {

log("emitting A");emitter.onNext("A");

log("emitting B");emitter.onNext("B");

log("Completing");emitter.onComplete();

subscribeOn()

log("Starting");final Observable<String> obs = simple();log("Created");obs.subscribe(

x -> log("Got " + x),Throwable::printStackTrace,() -> log("Completed")

298 | main | Starting

298 | main | Created

298 | main | Emitting A

298 | main | Got A

298 | main | Emitting B

298 | main | Got B

298 | main | Completed

298 | main | Exiting

log("Starting");final Observable<String> obs = simple();log("Created");obs.subscribeOn(Schedulers.io())

.subscribe(x -> log("Got " + x),Throwable::printStackTrace,() -> log("Completed")

);log("Exiting");

298 | main | Starting

298 | main | Created

298 | main | Exiting

301 | RxCachedThreadScheduler | Emitting A

301 | RxCachedThreadScheduler | Got A

301 | RxCachedThreadScheduler | Emitting B

301 | RxCachedThreadScheduler | Got B

301 | RxCachedThreadScheduler | Completed

observeOn()

Controls which Scheduler is used to invoke downstream

log(“Starting”);final Observable<String> obs = simple();log(“Created”);obs.observeOn(Schedulers.io())

.subscribe(x -> log(“Got ” + x),Throwable::printStackTrace,() -> log(“Completed”));

log("Exiting");

Use subcribeOn and observeOn

log(“Starting”);final Observable<String> obs = simple();log(“Created”);obs.subscribeOn(Schedulers.io())

.observeOn(Schedulers.io())

.subscribe(x -> log(“Got ” + x),Throwable::printStackTrace,() -> log(“Completed”)

);log("Exiting");

Schedulers

- Schedulers.newThread()

- Schedulers.io()

- Schedulers.computation()

- Schedulers.trampoline()

- Schedulers.single()

- AndroidSchedulers.mainThread()

Error Handling

//.....subscribe(

System.out::println,throwable -> showError());

Replacing errors with a fixed result using onErrorReturn()

onErrorReturn example

Observable<Income> income = person.flatMap(this::determineIncome).onErrorReturn(error -> Income.no())

private Observable<Income> determineIncome(Person person) {return Observable.error(new RuntimeException(“Foo”));

class Income {static Income no() {

return new Income(0);}

Timing Out When Events Do Not Occur

timeout example

Observable<String> confirmation() {Observable<String> delayBeforeCompletion =

Observable.<String>empty().delay(200, MILLISECONDS);

return Observable.just("a").delay(100, MILLISECONDS).concatWith(delayBeforeCompletion);

confirmation().timeout(110, MILLISECONDS).test().await().assertValue("a").assertError(TimeoutException.class);

Retrying After Failures

Observable<String> risky() {return Observable.fromCallable(() -> {

if (Math.random() < 0.1) {Thread.sleep((long) (Math.random() * 2000));return "OK";

} else {throw new RuntimeException("Transient");

risky().timeout(1, SECONDS).doOnError(th -> log.warn("Will retry", th)).retry().subscribe(log::info);

Thank you

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