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Rx Reactive Extensions 22 décembre 2015

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Problems to solve ● Callback hell

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Problems to solve ● Callback hell ● Chaining operations

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Problems to solve ● Callback hell ● Chaining operations

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Problems to solve ● Callback hell ● Chaining operations ● Threading is hard

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Problems to solve ● Callback hell ● Chaining operations ● Threading is hard CompletionService Delayed Executor ExecutorService Future RunnableFuture ScheduledExecutorService ScheduledFuture ThreadFactory BrokenBarrierException CountDownLatch CyclicBarrier Exchanger ForkJoinPool ForkJoinWorkerThread Phaser RecursiveAction RecursiveTask ScheduledThreadPoolExecutor Semaphore Thread AsyncTask Loader IntentService

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Problems to solve ● Callback hell ● Chaining operations ● Threading is hard ● Error handling

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Example: MyMTV Login Account User User User User User Profile Profile Profile Profile Profile Success!

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Example: RMN Slideshow: - collection of medias (images and videos) - images should be displayed as such - videos should display a preview

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Reactive Extensions

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Rx: Reactive Extensions ● Functional Reactive Programming : 1997 (40 years after Functional/OOP) ● Started by Microsoft for .NET ● RxJava: 2012 (Netflix) => ReactiveCocoa, RxAndroid

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Observable Pattern

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Observable single items multiple items synchronous T getData() Iterable getData() Collection getData() asynchronous Future getData() Observable getData()

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Subscriber event Iterable (pull) Observable (push) retrieve data T next() onNext(T) discover error throws Exception onError(Exception) complete returns onCompleted()

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Observable Pattern

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Creating an Observable Observable o = Observable.from("a", "b", "c"); def list = [5, 6, 7, 8] Observable o = Observable.from(list); Observable o = Observable.just("one object");

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Creating an Observable Observable.just(t); Observable.just(t1, t2, t3, t4, t5, ...); Observable.from(iterable); Observable.range(start, end); Observable.empty(); Observable.error(throwable); Observable.never(); Observable.interval(interval, unit); Observable.timer(delay, period, unit);

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Creating an Observable func myJust(element: E) -> Observable { return create { observer in observer.on(.Next(element)) observer.on(.Completed) return NopDisposable.instance } } myJust(0) .subscribeNext { n in print(n) }

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“Warmth” of an Observable

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Operators

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Observable Pattern

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Visualising operators

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map

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flatMap

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Solving RMN Observable medias = apiManager.getMediaSlideshow(exposition); Observable urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );

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Solving RMN Observable medias = apiManager.getMediaSlideshow(exposition); Observable urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );

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Solving RMN Observable medias = apiManager.getMediaSlideshow(exposition); Observable urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );

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Solving RMN Observable medias = apiManager.getMediaSlideshow(exposition); Observable urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );

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Solving RMN Observable medias = apiManager.getMediaSlideshow(exposition); Observable urls = medias.flatMap(media -> if (media.isImage()) { return Observable.just(media.getImageUrl()); } else { return apiManager.getYoutubePreviewImage(media); } );

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filter

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Solving MyMTV Login Account User User User User User Profile Profile Profile Profile Profile Success!

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Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);

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Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);

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Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);

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Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);

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Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);

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Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);

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Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);

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Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);

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Solving MyMTV Observable.just(mAccount).map(account -> return account.createUserIfNecessary(context); ).flatMap(account -> return Observable.from(account.getUserList().getUsers()); ).filter(user -> return user.getProfiles().isEmpty(); ).flatMap(user -> return user.createNewProfile(); ).subscribe(onNext, onError, onCompleted);

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merge

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merge vs concat

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concat example // Our sources Observable memory = ...; Observable disk = ...; Observable network = ...; // Retrieve the first source with data Observable source = Observable .concat(memory, disk, network) .first();

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flatMap vs concatMap

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switchMap

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skip

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distinct

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distinctUntilChanged

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retryWhen

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defaultIfEmpty - switchIfEmpty

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debounce

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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debounce

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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switchMap - switchOnNext

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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retryWhen

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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Text field -> search RxTextView.textChanges(searchEditText) .debounce(150, MILLISECONDS) .switchMap(Api::searchItems) .retryWhen(new RetryWithConnectivityIncremental(context, 5, 15, SECONDS)) .subscribe(updateList, t->showErrorToUser());

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timeout

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zip

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combineLatest

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combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each

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combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each

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combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each

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combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each

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combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each

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combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each

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combineLatest example emailChangeObservable = RxTextView.textChangeEvents(email); passwordChangeObservable = RxTextView.textChangeEvents(password); submitButton.setEnabled(false); // force-disable the button Observable.combineLatest(emailChangeObservable, passwordChangeObservable,(emailObs, pwdObs) -> { boolean emailCheck = emailObs.text().length() >= 3; boolean passwordCheck = pwdObs.text().length() >= 3; return emailCheck && passwordCheck; }).subscribe(aBoolean -> { submitButton.setEnabled(aBoolean); }); // submit button will only be clickable if both forms have more than 3 characters each

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Threading (and more)

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subscribeOn / observeOn myObservableServices.retrieveImage(url) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(bitmap -> myImageView.setImageBitmap(bitmap));

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subscribeOn / observeOn

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subscribeOn / observeOn Transformer applySchedulers() { return observable -> observable.subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); } Observable.from(someSource) .map(data -> manipulate(data)) .compose(applySchedulers()) .subscribe(data -> doSomething(data));

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subscribeOn / observeOn Transformer applySchedulers() { return observable -> observable.subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); } Observable.from(someSource) .map(data -> manipulate(data)) .compose(applySchedulers()) .subscribe(data -> doSomething(data));

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Transformer applySchedulers() { return observable -> observable.subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); } Observable.from(someSource) .map(data -> manipulate(data)) .compose(applySchedulers()) .subscribe(data -> doSomething(data)); subscribeOn / observeOn

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private Object slowBlockingMethod() { ... } public Observable newMethod() { return Observable.defer(() -> Observable.just(slowBlockingMethod())); } defer

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Cancelling subscriptions @Override public void onStart() { super.onStart(); mSubscriptions = new CompositeSubscription(); mSubscriptions.add(rxBus.toObserverable().subscribe(new Action1() { @Override public void call(Object event) { // ... }})); } @Override public void onStop() { super.onStop(); mSubscriptions.unsubscribe(); }

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Side effect operations observable.doOnSubscribe(action0); observable.doOnUnsubscribe(action0); observable.doOnNext(action1); observable.doOnCompleted(action0); observable.doOnError(action0); observable.doOnTerminate(action0); // before termination methods observable.finallyDo(action0); // after termination methods observable.doOnEach(action1); // next, completed or error observable.doOnRequest(action1);

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cache

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cache Observable request = service.getUserPhoto(id).cache(); Subscription sub = request.subscribe(photo -> handleUserPhoto(photo)); // ...When the Activity is being recreated... sub.unsubscribe(); // ...Once the Activity is recreated... request.subscribe(photo -> handleUserPhoto(photo));

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cache

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publish

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back pressure

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Questions? 22 décembre 2015