Saving lives with RxJavaShahar Barsheshet

About me

Shahar Barsheshet

shahar2k5

Talk agenda

● Intro to RxJava

● Why and How?

● Common Mistakesand some tips

Do You Rx?

Intro to Rx

Wikipedia:

reactive programming is a programming paradigm oriented around data flows and the

propagation of change. This means that it should be possible to express static or

dynamic data flows with ease in the programming languages used, and that the

underlying execution model will automatically propagate changes through the data flow.

RxJava ← Reactive eXtentions ← Reactive Programing

Mmmm…. Data Flow….

Intro to Rx

Definition from ReactiveX:ReactiveX is a library for composing asynchronous and event-based programs by using observable sequences.

It extends the observer pattern to support sequences of data and/or events and adds operators that allow you to compose sequences together declaratively while abstracting away concerns about things like low-level threading, synchronization, thread-safety, concurrent data structures, and non-blocking I/O.

The Problem

Concurrency

The Problem

Some solutions:

● AsyncTask○ Comfortable - nice callbacks○ Error handling sucks - Tuple??○ The lost Context○ Composing multiple calls… oh no!○ Testing… yeah right…

● Threading○ Very hard to handle concurrency○ Bugs are easy to create

● IntentService○ Easy to use○ Updating the UI isn't trivial○ Concurrency…???

The Solution

RxJava● Can easily join background operations● Easy error handling● Can be tied to lifecycle● Easy to test● Remove boilerplate code

RxJava with Android

● RxAndroid - Android Schedulers

● RxBinding - by Jake Wharton

● RxJava

compile 'com.jakewharton.rxbinding:rxbinding:1.0.0'

compile 'io.reactivex:rxandroid:1.2.1'compile 'io.reactivex:rxjava:1.2.6'

compile 'io.reactivex:rxjava:1.2.6'

Rx Concepts

● Observable and the observer contracts

● Operators

● Schedulers

The Observable

Observables emits data when you subscribe to them.

● onNext(0 … ∞)● onComplete(0 … 1)● onError(0 … 1)

onError() and onComplete() are exclusive.

Subscribers and Subscriptions

Once subscribing to an Observable, we get the Subscription object.

The Subscription describes the connection between the Observable and the observer.

As long as we are subscribed, we will get data emitted from the Observable.To stop the Observable from emitting more item, we just need to call

subscription.unsubscribe();

Error handling

When an error occurs, the Observable stop emitting data.onError(Throwable t) gets called so we can handle the error in a proper way.

What happens if we don't implement onError(Throwable t) ?

The Magazine...

Subscribing - creating the Subscription

Preparing dataData ready - user can observe

Error!!!Complete

ObservableObserver

Unsubscribe

Subscribers and Subscriptions

Subscription mySubscription = myIntegers.subscribe(new Subscriber<Integer>() { @Override public void onCompleted() { // YEY!! finished emitting all the integers }

@Override public void onError(Throwable e) { // something bad happened }

@Override public void onNext(Integer integer) { // we just got a new integer }});

Observable<Integer> myIntegers = Observable.just(1, 2, 3, 4, 5);

mySubscription.unsubscribe();

Operators

ReactiveX offers lots of operators to handle and manipulate data.

Creating Observables

● Just — convert an object or a set of objects into an Observable that emits that or those objects● Interval — create an Observable that emits a sequence of integers spaced by a particular time interval● Create — create an Observable from scratch by calling observer methods programmatically

Transforming Observables

● Map — transform the items emitted by an Observable by applying a function to each item

Combining Observables

● Merge — combine multiple Observables into one by merging their emissions● CombineLatest — when an item is emitted by either of two Observables, combine the latest item emitted by each

Observable via a specified function and emit items based on the results of this function

Operators - Map

Operators - Filter

Operators

Observable<Integer> myIntegers = Observable.just(1, 2, 3, 4, 5);

Observable<Integer> evenIntegers = myIntegers.filter(new Func1<Integer, Boolean>() { @Override public Boolean call(Integer integer) { return integer % 2 == 0; }});

mappedToString.subscribe();

// onNext("Just mapped 2")// onNext("Just mapped 4")// onComplete()

Observable<String> mappedToString = evenIntegers.map(new Func1<Integer, String>() { @Override public String call(Integer integer) { return "Just mapped " + integer; }});

Operators

Observable<Integer> myIntegers = Observable.just(1, 2, 3, 4, 5);

myIntegers.filter(new Func1<Integer, Boolean>() { @Override public Boolean call(Integer integer) { return integer % 2 == 0; }}).map(new Func1<Integer, String>() { @Override public String call(Integer integer) { return "Just mapped " + integer; }});

Lambda Expression

new Func1<String, Integer>(){ @Override public Integer call(String string) { return string.length(); }};

(String string) ->{ return string.length();};

string -> string.length();= =

Operators

myIntegers .filter(integer -> integer % 2 == 0) .map(integer -> "Just mapped " + integer);

Observable<Integer> myIntegers = Observable.just(1, 2, 3, 4, 5);myIntegers.filter(new Func1<Integer, Boolean>() { @Override public Boolean call(Integer integer) { return integer % 2 == 0; }}).map(new Func1<Integer, String>() { @Override public String call(Integer integer) { return "Just mapped " + integer; }});

From this:

To this:

Schedulers

By default, an Observable and the chain of operators that you apply to it will do its work, and will notify its observers, on the same thread on which its Subscribe method is called. The SubscribeOn operator changes this behavior by specifying a different Scheduler on which the Observable should operate.

● Schedulers.computation( ) meant for computational work such as event-loops and callback processing

● Schedulers.io( ) meant for I/O-bound work such as asynchronous performance of blocking I/O, this scheduler is backed by a thread-pool that will grow as needed

● AndroidSchedulers.mainThread( ) (using RxAndroid)

subscribeOn() and observeOn

AsyncTask

String userId = "102";

AsyncTask getUserTask = new AsyncTask<String, Void, User>() { @Override protected User doInBackground(String[] strings) { return ServerAPI.getUserProfile(strings[0]); }

@Override protected void onPostExecute(User user) { super.onPostExecute(user); mAdapter.add(user.firstName + " " + user.lastName); }};

getUserTask.execute(userId);

AsyncTask

String userId = "102";

Observable.just(userId) .map(id -> ServerAPI.getUserProfile(id)) .subscribe(user -> { mAdapter.add(user.firstName + " " + user.lastName); }, throwable -> { Toast.makeText(this, "An error occurred, please try again" , Toast.LENGTH_SHORT).show(); });

Observable.just(userId) .map(id -> ServerAPI.getUserProfile(id)) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(user -> { mAdapter.add(user.firstName + " " + user.lastName); }, throwable -> { Toast.makeText(this, "An error occurred, please try again" , Toast.LENGTH_SHORT).show(); });

TimerTask

//initialize the TimerTask's jobTimerTask timerTask = new TimerTask() { @Override public void run() { // Do some cool stuff // on the UI Thread }};

//set a new TimerTimer timer = new Timer();

//schedule the timer, after the first 5000ms// the TimerTask will run every 10000mstimer.schedule(timerTask, 5000, 10000);

TimerTask

Observable.interval(5000, 10000, TimeUnit.MILLISECONDS) .observeOn(AndroidSchedulers.mainThread()) .subscribe(interval -> { // Do some cool stuff

// on the UI Thread });

public static Observable<Long> interval(long initialDelay, long period, TimeUnit unit) { return interval(initialDelay, period, unit, Schedulers.computation());}

Search address using Google Places API

mEditText.addTextChangedListener(new TextWatcher() { @Override public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) { GetPlaces task = new GetPlaces(); String check = mEditText.getText().toString(); task.execute(check); }

@Override public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {}

@Override public void afterTextChanged(Editable editable) {}});

// get the list of predictions in an asynctaskclass GetPlaces extends AsyncTask<String, Void, ArrayList<String>> {

@Override protected ArrayList<String> doInBackground(String... args) { ArrayList<String> predictionsArr = new ArrayList<String>(); try { ServerAPI.getSuggestionsFromGoogleAPI(args[0]); } catch (Exception e) { e.printStackTrace(); } // return all the predictions based on the typing the in the search return predictionsArr; }

@Override protected void onPostExecute(ArrayList<String> result) { // update the list with new data }}

Search address using Google Places API - using RxJava

RxTextView.textChanges(mEditText) .debounce(300, TimeUnit.MILLISECONDS) .distinctUntilChanged() .filter(charSequence -> charSequence != null && charSequence.length() > 0) .map(charSequence -> ServerAPI.getSuggestionsFromGoogleAPI(charSequence)) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .doOnError(throwable -> { // show user something about this error }) .subscribe(strings -> { // update the list with new data });

Getting the current country

NetworkProvider

IP

GPS

Getting the current country

public Observable<CountryProvider> getCountryCode(){ Observable<CountryProvider> locationObservable = getCountryFromLocationProvider(); Observable<CountryProvider> ipObservable = getCountryFromNetwork(); Observable<CountryProvider> providerObservable = getCountryFromNetworkProvider();

return Observable.merge(providerObservable, locationObservable, ipObservable) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .startWith(new CountryProvider("il", CountryProviderType.DEFAULT)) .scan((countryProvider, countryProvider2) -> { if (countryProvider2 == null) { return countryProvider; } int value1 = countryProvider.getProviderType().getValue(); int value2 = countryProvider2.getProviderType().getValue(); return value1 > value2 ? countryProvider : countryProvider2; }) .distinctUntilChanged() .onErrorReturn(null);}

Getting the current country

mCountryManager.getCountryCode() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(countryProvider -> { Toast.makeText(this, "Got country " + countryProvider.getCountryCode() + " from provider: " + countryProvider.getProviderType().name() , Toast.LENGTH_LONG).show(); });

CommonMistakesAnd Tips

Default Schedulers

Observable.just("hello") .subscribe(); → happens on the current thread

Observable.just("hello") .delay(1000, TimeUnit.MILLISECONDS) .subscribe(); → happens on the computation thread

VS

Multiple SubscribeOn

Observable.just("Hello") .subscribeOn(Schedulers.io()) .map(string -> string.length()) .subscribeOn(Schedulers.computation()) .subscribe();

io()

ObserveOn

Observable.just("Hello") // current thread .observeOn(Schedulers.io()) .map(string -> string.length()) // io .observeOn(Schedulers.computation()) .subscribe(); // computation

Multiple observeOn do work as expected.

Memory leak

● Subscribers can leak!

● Use leakcanary

● Unsubscribe when leaving

Unsubscribe

Subscription subscription = Observable.just("Hello").subscribe();subscription.unsubscribe();

CompositeSubscription

Subscription myIntegerSubscription = myIntegers.subscribe(new Subscriber<Integer>() { @Override public void onCompleted() {} @Override public void onError(Throwable e) {} @Override public void onNext(Integer integer) {}});Subscription myStringSubscription = myStrings.subscribe(new Subscriber<String>() { @Override public void onCompleted() {} @Override public void onError(Throwable e) {} @Override public void onNext(String string) {}});compositeSubscription.add(myIntegerSubscription);compositeSubscription.add(myStringSubscription);

Observable<Integer> myIntegers = Observable.just(1, 2, 3, 4, 5);Observable<String> myStrings = Observable.just("one", "two", "three", "four", "five");

compositeSubscription.unsubscribe();// ORcompositeSubscription.clear();

CompositeSubscription compositeSubscription = new CompositeSubscription();

LifeCycle

private CompositeSubscription mSubscriptions;

@Overridepublic void onViewCreated(View view, @Nullable Bundle savedInstanceState) { super.onViewCreated(view, savedInstanceState); mSubscriptions = new CompositeSubscription();}

@Overridepublic void onDestroyView() { super.onDestroyView(); if (!mSubscriptions.isUnsubscribed()) mSubscriptions.unsubscribe();}

public void addSubscriptionToViewLifeCycle(Subscription subscription) { mSubscriptions.add(subscription);}

Thanks!By the way

We are hiring!Shahar Barsheshet

Source code