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 4IBSF5IF.FBM We provide food to schoolchildren in need – over 5.000.000 meals shared! It costs only €0.40 to feed one child for a day. www.sharethemeal.org Google Play Best of 2015 & Editor's Choice, SXSW 2015 Innovation Award 3FDJQFT
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DPNQMJDBUFE  create() – executed upon subscription but need to take care of contract calls public Observable exampleTooComplicated() { SharedPreferences prefs = context.getSharedPreferences("prefs", Context.MODE_PRIVATE); return Observable.create(new Observable.OnSubscribe() { @Override public void call(Subscriber subscriber) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(prefs.getBoolean("boolean", false)); if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } } }); } 3FDJQFT
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SJHIU  defer() – simple, but executed upon subscription  fromCallable() – the same, for methods that return values public Observable exampleJustRight() { SharedPreferences prefs = context.getSharedPreferences("prefs", Context.MODE_PRIVATE); return Observable.defer(new Func0>() { @Override public Observable call() { return Observable.just(prefs.getBoolean("boolean", false)); } }); } 3FDJQFT
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PQT List list = new ArrayList<>(); Observable.from(list) .map(aBoolean -> !aBoolean) //returns value .flatMap(aBoolean -> Observable.just(aBoolean.hashCode()) //returns observable .toList() //or .toSortedList() .subscribe(new Observer>() { ... 3FDJQFT
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4VCKFDUT  they're Hot observables – the values are generated independently of existence of subscribers  use them to send values to Observers outside creation block  enable you to have communication between the Observer and Observable-value generator  access onNext(), onError() and onCompleted() whenever you want  single-threaded by default, don't mix threads when calling onXXX()!  for thread safety, wrap them in a SerializedSubject() or call Subject.toSerialized().onXXX() 3FDJQFT
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DPOUE  AsyncSubject – remembers the last value – after onCompleted() subscribers receive the last value and the onCompleted() event – after onError() subscribers receive just the onError() event  ReplaySubject – remembers everything but can be limited (create(int bufferCapacity), createWithSize(int size), createWithTime(long time, TimeUnit unit, final Scheduler scheduler), createWithTimeAndSize(long time, TimeUnit unit, int size, final Scheduler scheduler)) 3FDJQFT
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0CTFSWFS public class MusicPlayer { public enum PLAYER_STATE {STOPPED, PLAYING} Observer playerObserver = new Observer() { @Override public void onNext(PLAYER_STATE state) { currentPlayerState = state; if (state == PLAYER_STATE.PLAYING) { startSong(); showPauseButton(); } else if (state == PLAYER_STATE.STOPPED) { stopSong(); showPlayButton(); } } ... }; } 3FDJQFT
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public class MusicPlayer { PLAYER_STATE currentPlayerState = PLAYER_STATE.STOPPED; BehaviorSubject playerStateSubject = BehaviorSubject.create(currentPlayerState); public MusicPlayer() { playerStateSubject.subscribe(playerObserver); } private void pressButton() { if (currentPlayerState == PLAYER_STATE.PLAYING) { playerStateSubject.onNext(PLAYER_STATE.STOPPED); } else if (currentPlayerState == PLAYER_STATE.STOPPED) { playerStateSubject.onNext(PLAYER_STATE.PLAYING); } } } 3FDJQFT
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 We don't need currentPlayerState, just use playerStateSubject.getValue()  Don't expose Subject to others: when offering them for subscribing, use getObservable() public Observable getPlayerStateObservable() { return playerStateSubject.asObservable(); }  Use Subscription to control Observer lifecycle! 3FDJQFT
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4VCTDSJQUJPO  Subscription is a relationship between the Observer and the Observable public MusicPlayer() { Subscription stateSub = playerStateSubject.subscribe(playerObserver); }  Subscription is returned by the subscribe() public MusicPlayer() { Subscription stateSub = playerStateSubject //Observable .filter(state -> state == PLAYING) //Observable .map(state -> someMethod()) //Observable .subscribe(playerObserver); //Subscription }  Very simple: isUnsubscribed(), unsubscribe() 3FDJQFT
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DPOUE To prevent multiple executions/subscriptions: public MusicPlayer() { if (mPlayerSubscription == null || mPlayerSubscription.isUnsubscribed()) { mPlayerSubscription = playerStateSubject.subscribe(playerObserver); } }  Important: unsubscribing has no impact on the observable or other subscriptions! 3FDJQFT
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4VCTDSJQUJPOT When you need to control multiple subscriptions at the same time: CompositeSubscription activitySubscriptions = new CompositeSubscription(); @Override protected void onCreate() { mPlayerSub = playerStateSubject.subscribe(playerObserver); mPlayerSub2 = playerStateSubject.subscribe(playerObserver2); activitySubscriptions = new CompositeSubscriptions(mPlayerSub, mPlayerSub2); } @Override protected void onResume() { mPlayerSub3 = playerStateSubject.subscribe(playerObserver3); activitySubscriptions.add(mPlayerSub3); } 3FDJQFT
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DPOUE When you need to control multiple subscriptions at the same time: removing with remove(), unsubscribing all with unsubscribe(), and clear() unsubscribes all and removes them from the CompositeSubscription: @Override protected void onPause() { mPlayerSub3 = playerStateSubject.subscribe(playerObserver3); activitySubscriptions.remove(mPlayerSub3); } @Override protected void onDestroy() { super.onDestroy(); if (activitySubscriptions.hasSubscriptions() && !activitySubscriptions.isUnsubscribed()) { activitySubscriptions.unsubscribe(); } } 3FDJQFT
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MJGFDZDMF  Manually, on the Activity or Fragment level – create when you want, unsubscribe in onPause()/onStop()/onDestroy()  Automatically, on the Activity or Fragment level – use https://github.com/trello/RxLifecycle public class MainActivity extends RxAppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { Observable.interval(1, TimeUnit.SECONDS) .compose(this.bindUntilEvent(ActivityEvent.PAUSE)) //binds to onPause() .subscribe(onCreateObserver); } } .compose(this.bindUntilEvent(ActivityEvent.DESTROY)) //binds to onDestroy() .compose(this.bindToLifecycle()) //binds automatically to opposite method (if called from onResume() it will be bound to onPause() One very important note: RxLifecycle doesn't call unsubscribe() but calls onCompleted() instead! 3FDJQFT
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HMPCBM  Manually on the global, Application level – create when you want, and unsubscribe? Never, so do the transactions atomically, close the observables and unsubscribe from activities/fragments: public class SplashActivity extends AppCompatActivity { Subscription mUserSubscription = Subscriptions.empty(); @Override protected void onCreate(Bundle savedInstanceState) { mUserManager.getUserObservable() .subscribe(user -> continue(), throwable -> showError(throwable)); } @Override protected void onDestroy() { if (!mUserSubscription.isUnsubscribed()) mUserSubscription.unsubscribe(); } } 3FDJQFT
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DPOUE public UserManager () { //from() will automatically call onCompleted() so no pending references Observable.from(loadUserFromSavedPreferences()) .subscribe(user -> mUserSubject.onNext(user), throwable -> mUserSubject.onError(throwable)); } Observable getUserObservable() { return mUserSubject.asObservable(); } }  There's no automated way to manage lifecycle on the global level! 3FDJQFT
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IBOEMJOH  sending onError() closes the subscription and no more events are sent!  onError() handles ALL errors in the chain!  to prevent this, use error handling methods: – onErrorReturn() - use other value – onErrorResumeNext() - use other observable – onExceptionResumeNext() - handles Exceptions but not Throwables mConfigurationManager.getCurrentConfigObservable() .onErrorReturn(config -> Config.Empty) .flatMap(config -> loadUserFromSavedPreferences()) .onErrorReturn(user -> User.Empty) .subscribe(user -> mUserSubject.onNext(user); 3FDJQFT
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TVCTDSJQUJPOT  the whole of the chain is an Observable until the subscribe()  if you don’t use error management (onErrorReturn()/onErrorResumeNext()…), all subscriptions have to have onError()– but that is always a good idea!!! Observable Config.Empty); Subscription configValidSub = configObservable .filter(config -> config != null && config != Config.Empty) .flatMap(config -> loadUserFromSavedPreferences()) .onErrorReturn(user -> User.Empty) .subscribe(user -> mUserSubject.onNext(user)); Subscription configInvalidSub = configObservable .filter(config -> config == null || config == Config.Empty) .subscribe(config -> Log.d("App", "config empty!"); 3FDJQFT
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DIBJOT  if you have a part of the chain that repeats itself – extract it in a Transformer () Subscription configValidUserValidSub = configObservable .filter(config -> config != null && config != Config.Empty) .flatMap(config -> loadUserFromSavedPreferences()) .onErrorReturn(user -> User.Empty) .filter(user -> user != User.Empty) .subscribe(user -> mUserSubject.onNext(user)); Subscription configValidUserInalidSub = configObservable .filter(config -> config != null && config != Config.Empty) .flatMap(config -> loadUserFromSavedPreferences()) .onErrorReturn(user -> User.Empty) .filter(user -> user == User.Empty) .subscribe(user -> Log.d("APP", "user empty!"); 3FDJQFT
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DPOUE Observable.Transformer convertConfigToUser() { return new Observable.Transformer() { @Override public Observable call(Observable configObservable) { return configObservable .filter(config -> config != null && config != Config.Empty) .flatMap(config -> loadUserFromSavedPreferences()) .onErrorReturn(user -> User.Empty); } }; } Subscription configValidUserValidSub = configObservable .compose(convertConfigToUser()) .filter(user -> user != User.Empty) .subscribe(user -> mUserSubject.onNext(user)); Subscription configValidUserInalidSub = configObservable .compose(convertConfigToUser()) .filter(user -> user == User.Empty) .subscribe(user -> Log.d("APP", "user empty!"); 3FDJQFT
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 NVMUJUISFBEJOH  RxJava is asynchronous by default, but not multithreaded by default!  use explicit methods to change the thread:  subscribeOn() – it changes the upstream thread (until that point)  observeOn() – it changes the downstream thread (after that point) Observable.Transformer convertConfigToUser() { return new Observable.Transformer() { @Override public Observable call(Observable configObservable) { return configObservable .filter(config -> config != null && config != Config.Empty) .flatMap(config -> loadUserFromSavedPreferences()) .onErrorReturn(user -> User.Empty) .subscribeOn(Schedulers.io()) //everything up to this uses io() thread .observeOn(AndroidSchedulers.mainThread()); // everything after this // uses UI thread } }; } 3FDJQFT
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DPOUE  RxJava Scheduler:  computation() – bound (limited by CPU cores)  io() - unbound  immediate() – executes immediately on current thread  trampoline() – executes after finishing, on current thread  newThread() – creates new thread  from(Executor) – use custom executor  test() – uses TestScheduler with manual scheduling controls  rxandroid library: AndroidScheduler.mainThread()  Multithreading is hard, RxJava makes it easier – but it's still not easy!  do not specify the thread unless you really need to 3FDJQFT
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SFBEJOHXBUDIJOH  https://github.com/ReactiveX/RxJava  RxJava Single discussion: https://github.com/ReactiveX/RxJava/issues/1594  RxJava Subscriber discussion: https://github.com/ReactiveX/RxJava/issues/792  New viewbinding library using RxJava: https://github.com/alter-ego/androidbound  ReactiveX homepage: http://reactivex.io/  Interactive marble diagrams for operators: http://www.rxmarbles.com/  Ben Christensen's talks: https://speakerdeck.com/benjchristensen/  David Karnok's Advanced RxJava blog: http://akarnokd.blogspot.hu/  Grokking Rx MEAP: http://bit.ly/grokking-rx 3FDJQFT
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