Sviluppare app event-driven con RxJava su Android

Sviluppare app event-driven con RxJava su Android

Rx

Boris D’AmatoAndroid Developer @

+BorisDAmato

@borisdamato

damatoboris

borisdamato

Sviluppare App event-driven con RxJava su Android - Boris D’Amato

Il Problema


Il Problema

UI Thread

Main Thread


La Soluzione

RxJava RxJava è un’implementazione delle Reactive Extensions per la Java VM

Una libreria per realizzare programmi asincroni ed event-based utilizzando sequenze di

observable.


Cosa significa “Reactive”?Un sistema Reattivo deve essere

ovvero

alle richieste degli utenti

a guasti ed errori

Responsivo Resiliente Elastico Orientato a messaggi

al carico di lavoro a eventi e messaggi

reagire


Reactive Programming

Erik Meijer Ben Christensen

Rx.Net RxJava

Dávid Karnok

RxJava


Reactive Programming

“Paradigma di programmazione basato su flussi di dati e propagazione dei cambiamenti” [Wikipedia]

Data flow Observer pattern Push vs Pull


Gli Attori

Observable Observer Subscriber Subject

Generatore di dati

Reagisce alla ricezione dei dati

Ibrido tra Observable e

Observer


Comunicazione Observable - Observer

Observer

subscribe

Observable

onNext()

onComplete()

onError()

onSubscribe()


Android Time!

RecyclerView

Lista dei contatti


Creazione di un Observableprivate Observable<String> getContacts() { return Observable.create(new ObservableOnSubscribe<String>() { @Override public void subscribe(ObservableEmitter<String> e) throws Exception { List<String> contacts = new ArrayList<>();

Cursor cursor = [...];while (cursor.moveToNext()) {

String displayName = [...]; contacts.add(displayName);

}cursor.close();

for (String contact : contacts) { if (e.isDisposed()) return; e.onNext(contact); } if (!e.isDisposed()) e.onComplete();}});}

onError(Throwable e)

onNext(T item)

onComplete()


Creazione di un Observable

List<Contact> contacts = [...];Observable.fromArray(contacts).subscribe([...]);

Observable.just()

.fromIterable().fromFuture()

.fromCallable()

.fromPublisher()

Observable.fromArray()

List<Contact> contacts = [...];Observable.just(contacts.get(0), contacts.get(1))

.subscribe([...]);


Creazione di un Observable

Observable.empty() Observable.never() Observable.throw()


Observer<Contact> observer = new Observer<Contact>() { @Override public void onSubscribe(Disposable d) { Log.d(TAG, "onSubscribe");

Log.d(TAG, "isDisposed: " + d.isDisposed()); }

@Override public void onNext(Contact item) { Log.d(TAG, "onNext"); adapter.addItem(item); }

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

@Override public void onComplete() { Log.d(TAG, "onComplete"); }};

Subscribe

List<Contact> contacts = [...];Observable.fromArray(contacts)

.subscribe(observer);


Filtering

Giorgio Carlo Andrea Gianni

Giorgio Gianni

getContacts().filter(new Predicate<Contact>() { @Override public boolean test(Contact contact) throws Exception { return contact.getName().startsWith("G"); }})

Filter


Filtering (Lambda Version)


Giorgio Gianni

getContacts().filter(contact -> contact.getName().startsWith("G"))Filter

https://github.com/evant/gradle-retrolambda


Filtering


Giorgio

getContacts().take(3)Take

Carlo Andrea


Filtering


getContacts().takeLast(3)TakeLast

Carlo Andrea Gianni


Filtering

Giorgio Carlo Giorgio Gianni

getContacts().distinct()Distinct

Carlo GianniGiorgio


Filtering

21

getTemperature().distinct()

21 20 19 20 21 22 23 23 21 22 21

21 20 19 22 23

Distinct


Filtering

21

getTemperature().distinctUntilChanged()

21 20 19 20 21 22 23 23 21 22 21

DistinctUntil

Changed

21 20 19 20 21 22 23 21 22 21


Filtering

21

getTemperature().sample(30, TimeUnit.SECONDS)

21 20 19 20 21 22 23 23 21 22 21

Sampleo

ThrottleLast

20 21

30 sec 30 sec


Filtering

21

getTemperature().throttleFirst(30, TimeUnit.SECONDS)

21 20 19 20 21 22 23 23 21 22 21

ThrottleFirst

30 sec 30 sec

21 21 22


Transforming


giorgio

getContacts().map((contact) -> {contact.setName(

contact.getName().toLowerCase());return contact;

})

Map

carlo andrea gianni


Combining


Giorgio

Observable.merge(getContacts(), getImportingContacts())Merge

Carlo Andrea Gianni

Marco Francesco

Marco Francesco


Combining

21° 22° 20° 18°

21° - 17:30

Zip

17:30 18:00 18:30 19:00

16°

22° - 18:00 20° - 18:30 18° - 19:00

Observable.zip(getTemperature(), getTime(), this::updateMonitor)


Torniamo ad Android...private Observable<Contact> getContacts() { return Observable.create(new ObservableOnSubscribe<Contact>() { @Override public void subscribe(ObservableEmitter<String> e) throws Exception { List<String> contacts = new ArrayList<>();

SharedPreferences prefs = getActivity().getPreferences(Context.MOODE_PRIVATE);Type contactType = new TypeToken<List<Contact>>(){}.getType();String contactsGson = prefs.getString(“CONTACTS”, “”);

if (!contactsGson.isEmpty())contacts = new Gson().fromJson(contactsGson, contactType);

for (Contact contact : contacts) {e.onNext(contact);

} if (!e.isDisposed()) e.onComplete();}});}


… e accade questo...

D/StrictMode: StrictMode policy violation; ~duration=253 ms: android.os.StrictMode$ StrictModeDiskReadViolation: policy=31violation=2 at android.os.StrictMode $AndroidBlockGuardPolicy. onReadFromDisk(StrictMode.java:1135)


SoluzionegetContacts()

.subscribeOn( Schedulers.io() )

.subscribe([...]);

Schedulers.

computation()

io()

immediate()

newThread()

trampoline()


… altro problema

android.view.ViewRoot$CalledFromWrongThreadException:

Only the original thread that created a view hierarchy can touch its views.

getContacts().subscribeOn(Schedulers.io()).observeOn( AndroidSchedulers.mainThread() ).subscribe([...]);

Soluzione


Nella pratica

● La ricerca debba essere eseguita ogni 500 millisecondi

Vogliamo che:

● La ricerca debba partire solo dopo che sia stati inseriti almeno 3 caratteri


RxBinding

compile 'com.jakewharton.rxbinding:rxbinding:0.4.0'compile 'com.jakewharton.rxbinding:rxbinding-support-v4:0.4.0'compile 'com.jakewharton.rxbinding:rxbinding-design:0.4.0'

[ . . .]

https://github.com/JakeWharton/RxBinding


Nella pratica

RxTextView.textChanges(searchField).debounce(500, TimeUnit.MILLISECONDS).filter( (charSequence) -> return charSequence.length() >= 3 ).subscribe( [...] )


Grazie.

@borisdamato

+BorisDAmato

Sviluppare app event-driven con RxJava su Android

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