Reactive Programming on Android

Erik Meijer - Rx .NET Ben Christensen - Rx Java

Introduction

Getting Started

Pull X Push

Getting Started

RxAndroid Dependency

compile 'io.reactivex:rxandroid:0.24.0'

Brings all you need

RXJava and RXAndroid

Anatomy

Observable.from(doLongNetworkOp())

.subcribeOn(Schedulers.io())

.observeOn(AndroidSchedulers.mainThread())

.subscribe(getObserver())

1. Observable

2. Observer

3. Schedulers

Anatomy

2. Observer.subscribe(getObserver())

private Observer<String> getObserver(){new Observer<String>() {

@Override public void onCompleted() { … }

@Override public void onError(Throwable e) { … }

@Override public void onNext(String string) { … } };}

Anatomy

Observable.from(doLongNetworkOp())

.subcribeOn(schedulers.io()).observeOn(AndroidSchedulers.mainThread())

.subscribe(getObserver())

1. Observable

2. Observer

3. Schedulers

Observable Observer

4. Subscription=

Subscription subscription = Observable.from(doLongNetworkOp())

.subcribeOn(Schedulers.io())

.observeOn(AndroidSchedulers.mainThread())

.subscribe(getObserver())

1. subscription.unsubscribe()

2. CompositeSubscription compSubscription;compSubscription.add(subscription);

3. compSubscription.unsubscribe()

Anatomy

Getting Started - Producer and Consumer

Stre

am

Observable ObserverEmits

item1

item2

item3

Uses item 1

Uses item 2

Uses item 3

onNext(item1)

onNext(item2)

onNext(item3)

no more items onCompleted() complete

Ops! Error… onError(error) Handles error

AsyncTask → Observable/Observer

new FindUserTask().execute(userId);

private class FindUserTask extends AsyncTask<Long, Void, Void>{ @Override protected void onPreExecute() { showLoading(); }

@Override protected User doInBackground(Long... params){ return userService.findUserById(params[0]); }

@Override protected void onPostExecute(User user){ mUserName.setText(user.getName()); hideLoading(); }}

Observable .just(userId) .flatMap(new Func1<Long, Observable<User>>(){ @Override public Observable<User> call(Long userId){ return Observable.just(userService.findUserById(userId); }).subscribeOn(Schedulers.io()) .subscribe( new Observer<User>() { @Override

public void onCompleted() { Log.d(TAG, "onCompleted"); hideLoading(); }

@Override public void onError(Throwable e) { Log.d(TAG, "onError " + e.getMessage()); }

@Override public void onNext(User user) { Log.d(TAG, "onNext"); mUserName.setText(user.getName()); } });

android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

Ops! Something went wrong

AsyncTask → Observable/Observer

Observable.just(userId) .flatMap(new Func1<Long, Observable<User>>(){ @Override public Observable<User> call(Long userId){ return Observable.just(service.findUserById(userId); }})

.subscribe(new Observer<User>() {

@Override public void onCompleted() { … }

@Override public void onError(Throwable e) { … }

@Override public void onNext(User user) { … } });

.subscribeOn(Schedulers.io())

.observeOn(AndroidSchedulers.mainThread())

Operators

● Create● From● Just● Filter● Map● Concat● Many others...

Observable.create(new Observable.OnSubscribe<Integer>() { @Override public void call(Subscriber<? super Integer> observer) { try { if (!observer.isUnsubscribed()) { for (int i = 1; i < 5; i++) { observer.onNext(i); } observer.onCompleted(); } } catch (Exception e) { observer.onError(e); } } } );

Operators - Create

Integer[] items = { 0, 1, 2, 3, 4, 5 };

Observable myObservable = Observable.from(items);

Operators - From

Observable.just(1, 2, 3) .subscribe(new Subscriber<Integer>() { @Override public void onNext(Integer item) { System.out.println(“onNext:” + item); }

@Override public void onError(Throwable error) { System.err.println(“Error: ” + error.getMessage()); }

@Override public void omCompleted() { System.out.println("Sequence complete. ”); } });

Operators - Just

Observable.just(1, 2, 3, 4) .filter(new Func1<Integer, Boolean>(){ @Override public Boolean call(Integer number){ return (number < 4); } })

.subscribe(new Subscriber<Integer>() {

@Override public void onCompleted() { Log.d(TAG, "Sequence complete"); }

@Override public void onError(Throwable e) { Log.d(TAG, "onError"); }

@Override public void onNext(Integer number) { Log.d(TAG, "onNext " + number); } });

onNext 1

onNext 2

onNext 3

Sequence complete

Operators - Filter

Operators - Map

Operators - Concat

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

http://rxmarbles.com

A Decision Tree of Observable OperatorsI want to emit only certain items from an Observable

by filtering out those that do not match some predicate Filter

that is, only the first item First

that is, only the first items Take

that is, only the last item Last

Operators - Many Others

Questions ?