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Introduction to RxJava for Android Developers Marcelo Benites

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Reactive Programming

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Reactive Programming

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ReactiveX is a combination of the best ideas from the Observer pattern, the Iterator pattern, and functional programming

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Easily create event streams or data streams. CREATE

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Easily create event streams or data streams. CREATE Compose and transform streams with query-like operators. COMBINE

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Compose and transform streams with query-like operators. COMBINE Subscribe to any observable stream to perform side effects. LISTEN Easily create event streams or data streams. CREATE

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RxJava

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public interface Dog {
 
 public String getName();
 
 public boolean isTrained();
 }

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public interface Dog {
 
 public String getName();
 
 public boolean isTrained();
 } public interface DogHandler {
 
 Observable trainDogs();
 }

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DogHandler john = DogHandlerFactory.get(DogHandlerFactory.JOHN);
 
 Observable trainedDogs = john.trainDogs();

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Create

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public class John implements DogHandler { 
 @Override public Observable trainDogs() {
 
 }
 }

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public class John implements DogHandler { 
 @Override public Observable trainDogs() {
 return Observable.just(new DummyDog("Marley"));
 }
 }

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public class John implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.from(
 Arrays.asList(new DummyDog("Marley"), 
 new DummyDog("Rocky"), 
 new DummyDog("Daisy")));
 }
 }

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public class John implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.fromCallable(() -> { 
 return new DummyDog("Marley");
 });
 }
 }

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public class John implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.defer(() -> {
 return Observable.just(new DummyDog("Marley"));
 });
 }
 }

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public class John implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.create(new Observable.OnSubscribe() {
 @Override public void call(Subscriber subscriber) {
 subscriber.onNext(new DummyDog("Marley"));
 subscriber.onNext(new DummyDog("Rocky"));
 subscriber.onCompleted();
 }
 });
 }
 }

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public class John implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.create(new Observable.OnSubscribe() {
 @Override public void call(Subscriber subscriber) {
 subscriber.onNext(new DummyDog("Marley"));
 subscriber.onNext(new DummyDog("Rocky"));
 subscriber.onCompleted();
 }
 });
 }
 }

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Combine

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public class John implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.from(
 Arrays.asList(new DummyDog("Marley"), 
 new DummyDog("Rocky"), 
 new DummyDog("Daisy")));
 }
 }

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public class John implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.from( Arrays.asList(new DummyDog("Marley"), 
 new DummyDog("Rocky"), 
 new DummyDog("Daisy")))
 .map(dummyDog -> trainDog(dummyDog));
 }
 
 private Dog trainDog(Dog dog) {
 return new TrainedDog(dog.getName());
 }
 }

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public class John implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.from( Arrays.asList(new DummyDog("Marley"), 
 new DummyDog("Rocky"), 
 new DummyDog("Daisy")))
 .map(dummyDog -> trainDog(dummyDog));
 }
 
 private Dog trainDog(Dog dog) {
 return new TrainedDog(dog.getName());
 }
 }

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public class John implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.from( Arrays.asList(new DummyDog("Marley"), 
 new DummyDog("Rocky"), 
 new DummyDog(“Daisy"))) .filter(dummyDog -> !dummyDog.getName().equals(“Rocky"))
 .map(dummyDog -> trainDog(dummyDog));
 }
 
 private Dog trainDog(Dog dog) {
 return new TrainedDog(dog.getName());
 }
 }

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public class Mary implements DogHandler {
 
 @Override public Observable trainDogs() {
 return Observable.just(new DummyDog("Rocky"))
 .map(dummyDog -> trainDog(dummyDog));
 }
 
 private Dog trainDog(Dog dog) {
 return new TrainedDog(dog.getName());
 }
 }

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DogHandler john = DogHandlerFactory.get(DogHandlerFactory.JOHN);
 
 Observable trainedDogs = john.trainDogs();

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DogHandler john = DogHandlerFactory.get(DogHandlerFactory.JOHN);
 DogHandler mary = DogHandlerFactory.get(DogHandlerFactory.MARY);
 
 Observable trainedDogs = Observable.merge(john.trainDogs(), mary.trainDogs());

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DogHandler john = DogHandlerFactory.get(DogHandlerFactory.JOHN);
 DogHandler mary = DogHandlerFactory.get(DogHandlerFactory.MARY);
 
 Observable trainedDogs = Observable.concat(john.trainDogs(), mary.trainDogs());

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public interface DogRepository {
 
 Observable storedDogs();
 
 }

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public class John implements DogHandler {
 
 private final DogRepository dogRepository;
 
 public John(DogRepository dogRepository) {
 this.dogRepository = dogRepository;
 }
 
 @Override public Observable trainDogs() {
 return dogRepository.storedDogs()
 .filter(storedDog -> (!storedDog.isTrained() 
 && !storedDog.getName().equals(“Rocky")))
 .map(dummyDog -> trainDog(dummyDog));
 }
 
 private Dog trainDog(Dog dummyDog) {
 return new TrainedDog(dummyDog.getName());
 }
 }

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DogHandler john = DogHandlerFactory.get(DogHandlerFactory.JOHN);
 DogHandler mary = DogHandlerFactory.get(DogHandlerFactory.MARY);
 
 Observable trainedDogs = Observable.concat(john.trainDogs(), mary.trainDogs());

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DogHandler john = DogHandlerFactory.get(DogHandlerFactory.JOHN);
 DogHandler mary = DogHandlerFactory.get(DogHandlerFactory.MARY);
 
 Observable trainedDogs = Observable.concat(john.trainDogs().take(3), mary.trainDogs());

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RxBindings

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Button button = (Button)findViewById(R.id.button); 
 Observable clicks = RxView.clicks(button)

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Button button = (Button) findViewById(R.id.button);
 DogHandler john = DogHandlerFactory.get(DogHandlerFactory.JOHN);
 
 Observable trainedDogs = RxView.clicks(button).flatMap(click -> john.trainDogs());

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Button button = (Button) findViewById(R.id.button);
 DogHandler john = DogHandlerFactory.get(DogHandlerFactory.JOHN);
 
 Observable trainedDogs = RxView.clicks(button).concatMap(click -> john.trainDogs());

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Listen

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trainedDogs.subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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Subscription subscription = trainedDogs
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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subscription.unsubscribe();

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RxLifecycle

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public class MainActivity extends RxAppCompatActivity {
 …
 }

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@Override protected void onResume() {
 super.onResume();
 trainedDogs
 .compose(bindToLifecycle())
 .subscribe(new Observer() {
 
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });
 }

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@Override protected void onResume() {
 super.onResume();
 trainedDogs
 .compose(bindUntilEvent(ActivityEvent.DESTROY))
 .subscribe(new Observer() {
 
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });
 }

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RxAppCompatActivity view = MainActivity.this;
 view.lifecycle()
 .filter(activityEvent -> activityEvent.equals(ActivityEvent.RESUME))
 .flatMap(resume -> john.trainDogs())
 .compose(view.bindUntilEvent(ActivityEvent.DESTROY))
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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RxAppCompatActivity view = MainActivity.this;
 view.lifecycle()
 .filter(activityEvent -> activityEvent.equals(ActivityEvent.RESUME))
 .flatMap(resume -> john.trainDogs())
 .compose(view.bindUntilEvent(ActivityEvent.DESTROY))
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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RxAppCompatActivity view = MainActivity.this;
 view.lifecycle()
 .filter(activityEvent -> activityEvent.equals(ActivityEvent.RESUME))
 .flatMap(resume -> john.trainDogs())
 .compose(view.bindUntilEvent(ActivityEvent.DESTROY))
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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RxAppCompatActivity view = MainActivity.this;
 view.lifecycle()
 .filter(activityEvent -> activityEvent.equals(ActivityEvent.RESUME))
 .flatMap(resume -> john.trainDogs())
 .compose(view.bindUntilEvent(ActivityEvent.DESTROY))
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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RxAppCompatActivity view = MainActivity.this;
 view.lifecycle()
 .filter(activityEvent -> activityEvent.equals(ActivityEvent.RESUME))
 .flatMap(resume -> john.trainDogs())
 .compose(view.bindUntilEvent(ActivityEvent.DESTROY))
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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RxAppCompatActivity view = MainActivity.this;
 view.lifecycle()
 .filter(activityEvent -> activityEvent.equals(ActivityEvent.RESUME))
 .flatMap(resume -> john.trainDogs())
 .compose(view.bindUntilEvent(ActivityEvent.DESTROY))
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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RxAppCompatActivity view = MainActivity.this;
 view.lifecycle()
 .filter(activityEvent -> activityEvent.equals(ActivityEvent.RESUME))
 .compose(view.bindUntilEvent(ActivityEvent.DESTROY)) .flatMap(resume -> john.trainDogs())
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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RxAppCompatActivity view = MainActivity.this;
 view.lifecycle()
 .filter(activityEvent -> activityEvent.equals(ActivityEvent.RESUME))
 .compose(view.bindUntilEvent(ActivityEvent.DESTROY)) .flatMap(resume -> john.trainDogs())
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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Threading

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Schedulers.io();
 
 Schedulers.computation();
 
 Schedulers.newThread();
 
 Schedulers.immediate();
 
 Schedulers.from(Executors.newSingleThreadExecutor());

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Schedulers.io();
 
 Schedulers.computation();
 
 Schedulers.newThread();
 
 Schedulers.immediate();
 
 Schedulers.from(Executors.newSingleThreadExecutor());

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Schedulers.io();
 
 Schedulers.computation();
 
 Schedulers.newThread();
 
 Schedulers.immediate();
 
 Schedulers.from(Executors.newSingleThreadExecutor());

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Schedulers.io();
 
 Schedulers.computation();
 
 Schedulers.newThread();
 
 Schedulers.immediate();
 
 Schedulers.from(Executors.newSingleThreadExecutor());

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Schedulers.io();
 
 Schedulers.computation();
 
 Schedulers.newThread();
 
 Schedulers.immediate();
 
 Schedulers.from(Executors.newSingleThreadExecutor());

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Schedulers.io();
 
 Schedulers.computation();
 
 Schedulers.newThread();
 
 Schedulers.immediate();
 
 Schedulers.from(Executors.newSingleThreadExecutor());

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public interface DogWebService {
 
 Dog getDog();
 
 }

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public class John implements DogHandler {
 
 private final DogWebService dogWebService;
 
 public John(DogWebService dogWebService) {
 this.dogWebService = dogWebService;
 }
 
 @Override public Observable trainDogs() {
 return Observable.fromCallable(() -> {
 return dogWebService.getDog();
 })
 .map(dummyDog -> trainDog(dummyDog));
 }
 
 private Dog trainDog(Dog dummyDog) {
 return new TrainedDog(dummyDog.getName());
 }
 }

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@Override public Observable trainDogs() {
 return Observable.fromCallable(() -> {
 return dogWebService.getDog();
 })
 .map(dummyDog -> trainDog(dummyDog)) .subscribeOn(Schedulers.io());
 }

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@Override public Observable trainDogs() {
 return Observable.fromCallable(() -> {
 return dogWebService.getDog();
 })
 .map(dummyDog -> trainDog(dummyDog)) .subscribeOn(Schedulers.io());
 }

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@Override public Observable trainDogs() {
 return Observable.fromCallable(() -> {
 return dogWebService.getDog();
 })
 .map(dummyDog -> trainDog(dummyDog)) .subscribeOn(Schedulers.io()) .subscribeOn(Schedulers.computation());
 }

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@Override public Observable trainDogs() {
 return Observable.fromCallable(() -> {
 return dogWebService.getDog();
 })
 .map(dummyDog -> trainDog(dummyDog)) .subscribeOn(Schedulers.io()) .subscribeOn(Schedulers.computation());
 }

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@Override public Observable trainDogs() {
 return Observable.just(dogWebService.getDog()) .subscribeOn(Schedulers.io()) .map(dummyDog -> trainDog(dummyDog));
 }
 ?

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@Override public Observable trainDogs() {
 return Observable.just(dogWebService.getDog()) .subscribeOn(Schedulers.io()) .map(dummyDog -> trainDog(dummyDog));
 }


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final TextView text = (TextView) findViewById(R.id.text);
 
 john.trainDogs()
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 text.setText(dog.getName());
 }
 });

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RxAndroid

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final TextView text = (TextView) findViewById(R.id.text);
 
 john.trainDogs() .observeOn(AndroidSchedulers.mainThread())
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 text.setText(dog.getName());
 }
 });

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final TextView text = (TextView) findViewById(R.id.text);
 
 john.trainDogs() .observeOn(AndroidSchedulers.mainThread())
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 text.setText(dog.getName());
 }
 });

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final TextView text = (TextView) findViewById(R.id.text);
 
 john.trainDogs() .observeOn(AndroidSchedulers.mainThread()) .observeOn(Schedulers.io())
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 text.setText(dog.getName());
 }
 });

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final TextView text = (TextView) findViewById(R.id.text);
 
 john.trainDogs() .observeOn(AndroidSchedulers.mainThread()) .observeOn(Schedulers.io())
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 text.setText(dog.getName());
 }
 });

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final TextView text = (TextView) findViewById(R.id.text);
 
 john.trainDogs() .observeOn(AndroidSchedulers.mainThread()) .doOnNext(trainedDog -> text.setText(trainedDog.getName())) .observeOn(Schedulers.io())
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 text.setText(dog.getName());
 }
 });

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final TextView text = (TextView) findViewById(R.id.text);
 
 john.trainDogs() .observeOn(AndroidSchedulers.mainThread()) .doOnNext(trainedDog -> text.setText(trainedDog.getName())) .observeOn(Schedulers.io())
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 text.setText(dog.getName());
 }
 });

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final TextView text = (TextView) findViewById(R.id.text);
 
 john.trainDogs() .observeOn(AndroidSchedulers.mainThread()) .doOnNext(trainedDog -> text.setText(trainedDog.getName())) .delay(5, TimeUnit.SECONDS)
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 text.setText(dog.getName());
 }
 });

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final TextView text = (TextView) findViewById(R.id.text);
 
 john.trainDogs() .observeOn(AndroidSchedulers.mainThread()) .doOnNext(trainedDog -> text.setText(trainedDog.getName())) .delay(5, TimeUnit.SECONDS)
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 text.setText(dog.getName());
 }
 });

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Error Handling

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john.trainDogs()
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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john.trainDogs()
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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john.trainDogs()
 .subscribe(new Observer() {
 @Override public void onCompleted() {
 
 }
 
 @Override public void onError(Throwable e) {
 
 }
 
 @Override public void onNext(Dog dog) {
 
 }
 });

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john.trainDogs()
 .subscribe(dog -> { /*Next dog*/});

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OnErrorNotImplementedException

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Thank You! Questions?