Sviluppare app event-driven con RxJava su Android

Sviluppare app event-driven con
RxJava su Android
Rx

Boris D’Amato
Android 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 Observable
private 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()

List<Contact> contacts = [...];
Observable.fromArray(contacts).subscribe([...])
;
Observable.just()
.fromIterable()
.fromFuture()
.fromCallable()
.fromPublisher()
Observable.fromArray()
Observable.just(contacts.get(0), contacts.get(1))
.subscribe([...]);

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
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)
Take
Last
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
Distinct
Until
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
Sample
o
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
Throttle
First
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$ StrictModeDiskReadViol
ation: policy=31violation=2 at
android.os.StrictMode
$AndroidBlockGuardPolicy. onReadFromDisk (Stri
ctMode.java:1135)

Soluzione
getContacts()
.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

More Related Content

Viewers also liked

Sviluppare app event-driven con RxJava su Android