RX

chalup.github.io ! " + @jchalupski +Jerzy Chalupski

RX?

public interface GitHubService {
 @GET("/users")
 List getUsers();
 
 @GET("/users/{user}/repos")
 List listRepos(@Path("user") User user);
 }
 
 public class User {
 String getLogin();
 }
 
 public class Repo {
 String getDescription(); User getOwner();
 }

GitHubService service = /* retrofit magic */
 
 for (User user : service.getUsers()) {
 for (Repo repo : service.listRepos(user)) {
 if (repo.getDescription().contains("android")) {
 /* send invitation email */
 break;
 }
 }
 }

public interface GitHubService {
 @GET("/users")
 List getUsers();
 
 @GET("/users/{user}")
 User getUserDetails(@Path("user") User user);
 
 @GET("/users/{user}/repos")
 List listRepos(@Path("user") User user);
 }
 
 public class User {
 String getLogin();
 String getLocation();
 }
 
 public class Repo {
 String getName();
 String getDescription();
 String getLanguage();
 boolean isFork(); User getOwner();
 }

GitHubService service = /* retrofit magic */
 
 for (User user : service.getUsers()) {
 for (Repo repo : service.listRepos(user)) {
 boolean isAndroidRepo =
 repo.getDescription().contains("android") ||
 repo.getName().contains("android");
 boolean writtenInJava = repo.getLanguage().equals("Java");
 if (isAndroidRepo && writtenInJava && !repo.isFork()) {
 if (service.getDetails(user).getLocation().equals("Kraków")) { /* send invitation email */
 }
 break;
 }
 }
 }

public interface GitHubService {
 @GET("/users")
 List getUsers();
 
 @GET("/users/{user}")
 User getUserDetails(@Path("user") User user);
 
 @GET("/users/{user}/repos")
 List listRepos(@Path("user") User user);
 }
 
 public class User {
 String getLogin();
 String getLocation();
 }
 
 public class Repo {
 String getName();
 String getDescription();
 String getLanguage();
 boolean isFork(); User getOwner();
 }

public interface GitHubService {
 @GET("/users")
 void getUsers(Callback> users);
 
 @GET("/users/{user}")
 void getUserDetails(@Path("user") User user, Callback …);
 
 @GET("/users/{user}/repos")
 void listRepos(@Path("user") User user, Callback> …); }
 
 public class User {
 String getLogin();
 String getLocation();
 }
 
 public class Repo {
 String getName();
 String getDescription();
 String getLanguage();
 boolean isFork(); User getOwner();
 }

GitHubService service = /* retrofit magic */
 
 service.getUsers(new Callback>() {
 @Override
 public void success(List users, Response response) {
 for (User user : users) {
 service.listRepos(user, new Callback>() {
 @Override
 public void success(List repos, Response response) {
 for (Repo repo : repos) {
 boolean isAndroidRepo = repo.getDescription().contains("android") || repo.getName().contains("android");
 boolean writtenInJava = repo.getLanguage().equals("Java");
 if (isAndroidRepo && writtenInJava && !repo.isFork()) {
 service.getUserDetails(user, new Callback() {
 @Override
 public void success(User user, Response response) {
 if (user.getLocation().equals("Kraków")) {
 /* send invitation email */
 }
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });
 break;
 }
 }
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });
 }
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });


GitHubService service = /* retrofit magic */
 
 service.getUsers(new Callback>() {
 @Override
 public void success(List users, Response response) {
 for (User user : users) {
 service.listRepos(user, new Callback>() {
 @Override
 public void success(List repos, Response response) {
 for (Repo repo : repos) {
 boolean isAndroidRepo = repo.getDescription().contains("android") || repo.getName().contains("android");
 boolean writtenInJava = repo.getLanguage().equals("Java");
 if (isAndroidRepo && writtenInJava && !repo.isFork()) {
 service.getUserDetails(user, new Callback() {
 @Override
 public void success(User user, Response response) {
 if (user.getLocation().equals("Kraków")) {
 /* send invitation email */
 }
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });
 break;
 }
 }
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });
 }
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });


FP 101

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filter( )

filter( )

filter( ) map( )

filter( ) map( )

filter( ) map( ) flatMap( )

filter( ) map( ) flatMap( )

filter map flatMap Java 8 Stream API

filter transform transformAndConcat Guava FluentIterable

select map flat_map Ruby Enumerable

Where Select SelectMany C# LINQ

GitHubService service = /* retrofit magic */
 
 for (User user : service.getUsers()) {
 for (Repo repo : service.listRepos(user)) {
 boolean isAndroidRepo =
 repo.getDescription().contains("android") ||
 repo.getName().contains("android");
 boolean writtenInJava = repo.getLanguage().equals("Java");
 if (isAndroidRepo && writtenInJava && !repo.isFork()) {
 if (service.getDetails(user).getLocation().equals("Kraków")) { /* send invitation email */
 }
 break;
 }
 }
 }

GitHubService service = /* retrofit magic */
 
 service.getUsers().stream()
 .flatMap(user -> service.listRepos(user).stream())
 .filter(repo -> repo.getName().contains(“android") ||
 repo.getDescription().contains("android"))
 .filter(repo -> repo.getLanguage().equals("Java"))
 .filter(repo -> !repo.isFork())
 .map(Repo::getOwner)
 .distinct()
 .map(service::getUserDetails)
 .filter(user -> user.getLocation().equals("Kraków"))
 .forEach(user -> { /* send invitation email */ });

RX 101

TAKEAWAY #1 Observable == Iterable

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public interface GitHubService {
 @GET("/users")
 void getUsers(Callback> users);
 }
 service.getUsers(new Callback>() {
 @Override
 public void success(List users, Response response) {
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });


public interface GitHubService {
 @GET(“/users") Observable> getUsers(); } 
 service.getUsers().subscribe(
 new Action1>() {
 @Override
 public void call(List users) { // onNext
 }
 },
 new Action1() {
 @Override
 public void call(Throwable throwable) { // onError
 }
 }
 );

filter map flatMap RxJava Operators

filter map flatMap RxJava Operators http://reactivex.io/documentation/operators.html

GitHubService service = /* retrofit magic */
 
 service.getUsers().stream()
 .flatMap(user -> service.listRepos(user).stream())
 .filter(repo -> repo.getName().contains(“android") ||
 repo.getDescription().contains("android"))
 .filter(repo -> repo.getLanguage().equals("Java"))
 .filter(repo -> !repo.isFork())
 .map(Repo::getOwner)
 .distinct()
 .map(service::getUserDetails)
 .filter(user -> user.getLocation().equals("Kraków"))
 .forEach(user -> { /* send invitation email */ });

public interface GitHubService {
 @GET("/users")
 List getUsers();
 
 @GET("/users/{user}")
 User getUserDetails(@Path("user") User user);
 
 @GET("/users/{user}/repos")
 List listRepos(@Path("user") User user);
 }
 
 public class User {
 String getLogin();
 String getLocation();
 }
 
 public class Repo {
 String getName();
 String getDescription();
 String getLanguage();
 boolean isFork(); User getOwner();
 }

public interface GitHubService {
 @GET("/users")
 Observable> getUsers();
 
 @GET("/users/{user}")
 Observable getUserDetails(@Path("user") User user);
 
 @GET("/users/{user}/repos")
 Observable> listRepos(@Path("user") User user); }
 
 public class User {
 String getLogin();
 String getLocation();
 }
 
 public class Repo {
 String getName();
 String getDescription();
 String getLanguage();
 boolean isFork(); User getOwner();
 }

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .flatMap(Observable::from)
 .flatMap(service::listRepos)
 .flatMap(Observable::from)
 .filter(repo -> repo.getName().contains("android") ||
 repo.getDescription().contains("android"))
 .filter(repo -> repo.getLanguage().equals("Java"))
 .filter(repo -> !repo.isFork())
 .map(Repo::getOwner)
 .distinct()
 .flatMap(service::getUserDetails)
 .filter(user -> user.getLocation().equals("Kraków"))
 .subscribe(user -> { /* send invitation email */ });

GitHubService service = /* retrofit magic */
 
 service.getUsers().stream()
 .flatMap(user -> service.listRepos(user).stream()) 
 .filter(repo -> repo.getName().contains(“android") ||
 repo.getDescription().contains("android"))
 .filter(repo -> repo.getLanguage().equals("Java"))
 .filter(repo -> !repo.isFork())
 .map(Repo::getOwner)
 .distinct()
 .map(service::getUserDetails)
 .filter(user -> user.getLocation().equals("Kraków"))
 .forEach(user -> { /* send invitation email */ });

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .flatMap(Observable::from)
 .flatMap(service::listRepos)
 .flatMap(Observable::from)
 .filter(repo -> repo.getName().contains("android") ||
 repo.getDescription().contains("android"))
 .filter(repo -> repo.getLanguage().equals("Java"))
 .filter(repo -> !repo.isFork())
 .map(Repo::getOwner)
 .distinct()
 .flatMap(service::getUserDetails)
 .filter(user -> user.getLocation().equals("Kraków"))
 .subscribe(user -> { /* send invitation email */ });

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .flatMap(Observable::from)
 .flatMap(service::listRepos)
 .flatMap(Observable::from)
 .filter(repo -> repo.getName().contains("android") ||
 repo.getDescription().contains("android"))
 .filter(repo -> repo.getLanguage().equals("Java"))
 .filter(repo -> !repo.isFork())
 .map(Repo::getOwner)
 .distinct()
 .flatMap(service::getUserDetails)
 .filter(user -> user.getLocation().equals("Kraków"))
 .subscribe(user -> { /* send invitation email */ },
 error -> { /* report to analytics */ }
 );

GitHubService service = /* retrofit magic */
 
 service.getUsers(new Callback>() {
 @Override
 public void success(List users, Response response) {
 for (User user : users) {
 service.listRepos(user, new Callback>() {
 @Override
 public void success(List repos, Response response) {
 for (Repo repo : repos) {
 boolean isAndroidRepo = repo.getDescription().contains("android") || repo.getName().contains("android");
 boolean writtenInJava = repo.getLanguage().equals("Java");
 if (isAndroidRepo && writtenInJava && !repo.isFork()) {
 service.getUserDetails(user, new Callback() {
 @Override
 public void success(User user, Response response) {
 if (user.getLocation().equals("Kraków")) {
 /* send invitation email */
 }
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });
 break;
 }
 }
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });
 }
 }
 
 @Override
 public void failure(RetrofitError error) {
 }
 });


RX!

RX! db access user input touch events validation web requests

No content

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .flatMap(Observable::from)
 .flatMap(service::listRepos)
 .flatMap(Observable::from)
 .filter(repo -> repo.getName().contains("android") ||
 repo.getDescription().contains("android"))
 .filter(repo -> repo.getLanguage().equals("Java"))
 .filter(repo -> !repo.isFork())
 .map(Repo::getOwner)
 .distinct()
 .flatMap(service::getUserDetails)
 .filter(user -> user.getLocation().equals("Kraków"))
 .subscribe(user -> { /* send invitation email */ },
 error -> { /* report to analytics */ }
 );

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .flatMap(new Func1, Observable extends User>>() {
 @Override
 public Observable extends User> call(List users) {
 return Observable.from(users);
 }
 })
 .flatMap(new Func1>>() {
 @Override
 public Observable extends List> call(User user) {
 return service.listRepos(user);
 }
 })
 .flatMap(new Func1, Observable extends Repo>>() {
 @Override
 public Observable extends Repo> call(List repos) {
 return Observable.from(repos);
 }
 })
 .filter(new Func1() {
 @Override
 public Boolean call(Repo repo) {
 return repo.getName().contains("android") ||
 repo.getDescription().contains("android");
 }
 })
 .filter(new Func1() {
 @Override
 public Boolean call(Repo repo) {
 return repo.getLanguage().equals("Java");
 }
 })
 .filter(new Func1() {
 @Override
 public Boolean call(Repo repo) {
 return !repo.isFork();
 }
 })
 .map(new Func1() {
 @Override
 public User call(Repo repo) {
 return repo.getOwner();
 }
 })
 .distinct()
 .flatMap(new Func1>() {
 @Override
 public Observable extends User> call(User user) {
 return service.getUserDetails(user);
 }
 })
 .filter(new Func1() {
 @Override
 public Boolean call(User user) {
 return user.getLocation().equals("Kraków");
 }
 })
 .subscribe(
 new Action1() {
 @Override
 public void call(User user) { /* send invitation email */ }
 },
 new Action1() {
 @Override
 public void call(Throwable error) { /* report to analytics */ }
 }
 );


! orfjackal/retrolambda

! evant/gradle-retrolambda

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RX @ $

! ReactiveX/RxAndroid

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .map(it -> { /* time consuming operation */ } )
 .subscribe( /* show users on UI */ );

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .subscribeOn(Schedulers.io())
 .observeOn(Schedulers.computation())
 .map(it -> { /* time consuming operation */ } )
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe( /* show users on UI */ );

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .subscribeOn(Schedulers.io())
 .observeOn(Schedulers.computation())
 .map(it -> { /* time consuming operation */ } )
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe( /* show users on UI */ ); subscribeOn(): “Create the Observable on this thread”

observeOn(): “Perform all other operations on this thread” GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .subscribeOn(Schedulers.io())
 .observeOn(Schedulers.computation())
 .map(it -> { /* time consuming operation */ } )
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe( /* show users on UI */ );

! dlew/android-subscription-leaks

AppObservable.bindFoo() Simple & composable May leak

RxActivity / RxFragment Never leaks Requires base class

Never leaks Requires base class RoboMapsListViewSupportObservableActiv RxActivity / RxFragment

! ReactiveX/RxAndroid

WidgetObservable ViewObservable ContentObservable

WidgetObservable
 .text(textView)
 .filter(t -> t.text().length() > 2)
 .debounce(300, TimeUnit.MILLISECONDS)
 .observeOn(Schedulers.io())
 .map( /* fetch suggestions */ )
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe( /* show suggestions in autocomplete */ );

WidgetObservable
 .text(textView)
 .filter(t -> t.text().length() > 2)
 .observeOn(Schedulers.io())
 .map( /* fetch suggestions */ )
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe( /* show suggestions in autocomplete */ );

Preconditions.checkState(isUserAMonkey()); WidgetObservable
 .text(textView)
 .filter(t -> t.text().length() > 2)
 .observeOn(Schedulers.io())
 .map( /* fetch suggestions */ )
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe( /* show suggestions in autocomplete */ );

https://github.com/ReactiveX/RxJava/wiki/Backpressure Preconditions.checkState(isUserAMonkey()); WidgetObservable
 .text(textView)
 .filter(t -> t.text().length() > 2)
 .observeOn(Schedulers.io())
 .map( /* fetch suggestions */ )
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe( /* show suggestions in autocomplete */ );

RX @ !

I want to… • load data in background, • process data in background, • cache processed data, • subscribe on changes and reload automatically… • …unless user left the UI which needs this data, in that case just mark the data as dirty and reload as needed, • have a basic backpressure handling.

! futuresimple/android-db-commons

public class RxLoaderManager {
 public RxLoaderManager(Fragment fragment);
 
 public static abstract class LoaderBuilder {
 public LoaderBuilder(int loaderId);
 protected abstract Loader onCreateLoader(Context context);
 }
 
 public Observable load(LoaderBuilder loaderBuilder); }

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .flatMap(Observable::from)
 .flatMap(service::listRepos)
 .flatMap(Observable::from)
 .filter(repo -> repo.getName().contains("android") ||
 repo.getDescription().contains("android"))
 .filter(repo -> repo.getLanguage().equals("Java"))
 .filter(repo -> !repo.isFork())
 .map(Repo::getOwner)
 .distinct()
 .flatMap(service::getUserDetails)
 .filter(user -> user.getLocation().equals("Kraków"))
 .subscribe(user -> { /* send invitation email */ });

GitHubService service = /* retrofit magic */
 
 service.getUsers()
 .flatMap()
 .flatMap()
 .flatMap()
 .filter( )
 .filter()
 .filter()
 .map()
 .distinct()
 .flatMap()
 .filter()
 .subscribe();

GitHubService service = /* retrofit magic */
 
 Observable t = service.getUsers()
 .flatMap()
 .flatMap()
 .flatMap(); Observable u = t .filter() .map() .flatMap() .distinct(); Observable v = t .filter() .map() .filter(); Observable.combineLatest(u, v) .distinct()
 .flatMap()
 .filter()
 .subscribe();

GitHubService service = /* retrofit magic */
 
 Observable t = service.getUsers()
 .flatMap()
 .flatMap()
 .flatMap(); Observable u = t .filter() .map() .flatMap() .distinct(); Observable v = t .filter() .map() .filter(); Observable.combineLatest(u, v) .distinct()
 .flatMap()
 .filter()
 .subscribe();

/*
 RxFlowGraph
 deal ~> b1 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~> assoc_contact_ids.in1
 b3 ~> assoc_contact_ids.in2
 assoc_contact_ids.out ~> assoc_contacts_list ~> associated_contact_data.in1
 b1 ~> primary_contact ~~~> b3 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~> associated_contact_data.in2
 b1 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~> associated_contact_data.in3
 b1 ~> owner_id ~> b2 ~> users_with_contacts_permission ~> permissions_map.in1
 b2 ~> users_with_accounts_permission ~> permissions_map.in2
 permissions_map.out ~> associated_contact_data.in4
 associated_contact_data.out ~>
 
 .subscribe(
 onNext ->
 );
 */
 • Inspired by Akka Streams (http://goo.gl/gjG4FZ) • Java API & implementation ~ready, but a bit ugly • Big pain: RxFlowGraph elements != Observables • To be revisited if/when Kotlin is officially supported?

RECAP

Observable == Iterable

GOOD Escape from callback hell

GOOD Single point of error handling

GOOD Highlights spaghetti code

GOOD Highlights sloppy state usage

BAD Lifecycle handling

UGLY Anonymous classes boilerplate

HOT or NOT?

HOT or NOT? HOT in WidgetObservables

HOT or NOT? HOT in Retrofit

HOT or NOT? HOT in complex db access

HOT or NOT? NOT hot everywhere

“Well, Mr. Frankel, who started this program, began to suffer from the computer disease that anybody who works with computers now knows about. It's a very serious disease and it interferes completely with the work. The trouble with computers is you *play* with them. They are so wonderful. You have these switches - if it's an even number you do this, if it's an odd number you do that - and pretty soon you can do more and more elaborate things if you are clever enough, on one machine. After a while the whole system broke down. Frankel wasn't paying any attention; he wasn't supervising anybody. The system was going very, very slowly - while he was sitting in a room figuring out how to make one tabulator automatically print arc- tangent X, and then it would start and it would print columns and then bitsi, bitsi, bitsi, and calculate the arc-tangent automatically by integrating as it went along and make a whole table in one operation. Absolutely useless. We *had* tables of arc-tangents. But if you've ever worked with computers, you understand the disease - the *delight* in being able to see how much you can do. But he got the disease for the first time, the poor fellow who invented the thing.” ― Richard P. Feynman, Surely You're Joking, Mr. Feynman!

?

Thanks.