Android Reactive Programming with RxJava

In a world where there is a smartphone in every pocket, designing and building applications that can run smoothly and deliver the User Experience that users deserve, it’s the only way to go. Reactive Programming with RxJava will help you to beat Android Platform limitations to create astonishing Android Apps.
This talk will be a practical journey from basic Reactive Programming and Observer Pattern concepts to the main feature of RxJava, with code examples and a real-world app.
You will learn how to create an Observable “from scratch”, from a list or from a function you already have in your code base. You will learn how to filter an Observable sequence to create a new sequence containing only the values you want; you will learn how to apply a function to an Observable, how to concatenate or merge Observables. I’ll show how to enjoy RxAndroid Schedulers to overcome the threading and concurrency hell in Android.
I will close the talk with a practical example about RxJava + Retrofit, to easily communicate with a REST API.

Transcript

1. Ivan Morgillo Author of RxJava Essentials by Packt Publishing Author of Gratis Ebooks for Kindle
2. Android Reactive Programming with RxJava
3. Reactive Programming Ben Christensen - RxJava Erik Meijer - Rx .Net
4. RxJava • Data flow • Observer pattern • Push vs Pull
5. Observer Pattern • Notifications • Automation • Cause-Effect
6. RxJava Observer Pattern • Observable • Observer • Subscriber • Subject
7. RxJava Observer Pattern • Observable • Observer • Subscriber • Subject • OnNext() • OnError() • OnCompleted()
8. RxJava Observer Pattern Observable Observer time item1 onNext(item1) Use item1 item2 item3 onNext(item2) onNext(item3) Use item2 Use item3
9. Please, show some Android • Standand Android app • A bit of Material Design • A RecyclerView • A list of installed apps
10. Create an Observable create() subscriber.onNext() subscriber.onCompleted() private Observable<AppInfo> getApps() { return Observable .create(subscriber -> { List<AppInfoRich> apps = new ArrayList<>(); final Intent mainIntent = new Intent(Intent.ACTION_MAIN, null); mainIntent.addCategory(Intent.CATEGORY_LAUNCHER); List<ResolveInfo> infos = getActivity().getPackageManager() .queryIntentActivities(mainIntent, 0); for (ResolveInfo info : infos) { apps.add(new AppInfoRich(getActivity(), info)); } for (AppInfoRich appInfo : apps) { Bitmap icon = Utils.drawableToBitmap(appInfo.getIcon()); String name = appInfo.getName(); String iconPath = mFilesDir + "/" + name; Utils.storeBitmap(App.instance, icon, name); if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(new AppInfo(name, iconPath, appInfo.getLastUpdateTime())); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }); }
11. Create an Observable create() subscriber.onNext() subscriber.onCompleted() private Observable<AppInfo> getApps() { return Observable .create(new Observable.OnSubscribe<AppInfo>() { @Override public void call(Subscriber<? super AppInfo> subscriber) { List<AppInfoRich> apps = new ArrayList<>(); final Intent mainIntent = new Intent(Intent.ACTION_MAIN, null); mainIntent.addCategory(Intent.CATEGORY_LAUNCHER); List<ResolveInfo> infos = getActivity().getPackageManager().queryIntentActivities(mainIntent, 0); for (ResolveInfo info : infos) { apps.add(new AppInfoRich(getActivity(), info)); } for (AppInfoRich appInfo : apps) { Bitmap icon = Utils.drawableToBitmap(appInfo.getIcon()); String name = appInfo.getName(); String iconPath = mFilesDir + "/" + name; Utils.storeBitmap(App.instance, icon, name); if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(new AppInfo(name, iconPath, appInfo.getLastUpdateTime())); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } } }); }
12. Create an Observable Observable.from() List<AppInfo> appsList = [...] Observable.from(appsList) .subscribe(...) Observable.just() List<AppInfo> apps = ApplicationsList.getInstance().getList(); AppInfo appOne = apps.get(0); AppInfo appTwo = apps.get(1); AppInfo appThree = apps.get(2); Observable<AppInfo> threeOfThem = Observable.just(appOne, appTwo, appThree); threeOfThem.subscribe(...) Observable.empty() Observable.never() Observable.throw()
13. Subscribe and react mRecyclerView.setLayoutManager(new LinearLayoutManager(view.getContext())); mAdapter = new ApplicationAdapter(new ArrayList<>(), R.layout.applications_list_item); mRecyclerView.setAdapter(mAdapter); mSwipeRefreshLayout.setColorSchemeColors(getResources().getColor(R.color.myPrimaryColor)); mSwipeRefreshLayout.setProgressViewOffset(false, 0, (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 24, getResources().getDisplayMetrics())); // Progress mSwipeRefreshLayout.setEnabled(false); mSwipeRefreshLayout.setRefreshing(true); mRecyclerView.setVisibility(View.GONE); Observable.from(apps).subscribe(observer);
14. Subscribe and react Observer<AppInfo> observer = new Observer<AppInfo>() { @Override public void onCompleted() { mSwipeRefreshLayout.setRefreshing(false); Toast.makeText(getActivity(), "Here is the list!", Toast.LENGTH_LONG).show(); } @Override public void onError(Throwable e) { Toast.makeText(getActivity(), "Something went wrong!", Toast.LENGTH_SHORT).show(); mSwipeRefreshLayout.setRefreshing(false); } @Override public void onNext(AppInfo appInfo) { mAddedApps.add(appInfo); mAdapter.addApplication(mAddedApps.size() - 1, appInfo); } };
15. Subscribe and react I'm not buying it!! Show more!!!!
16. Filtering .subscribe(observer); Observer<AppInfo> observer = new Observer<AppInfo>() { @Override public void onCompleted() { [...] } @Override public void onError(Throwable e) { [...] } @Override public void onNext(AppInfo appInfo) { [...] } }; .filter((appInfo) -> appInfo.getName().startsWith("C")) getApps()
17. Filtering
18. Take this! getApps() .subscribe(observer); .take(3)
19. Take this! getApps() .subscribe(observer); .takeLast(3)
20. I hate duplicates! getApps() .subscribe(observer); .take(3) .repeat(3) .distinct()
21. I hate duplicates! currentTemperature() .subscribe(observer); .distinctUntilChanged()
22. Loosen it up a bit currentTemperature() .subscribe(observer); .sample(30, TimeUnit.SECONDS) currentTemperature() .subscribe(observer) .throttleFirst(30, TimeUnit.SECONDS)
23. Transforming Observable .from(apps) .subscribe(observer); .map((AppInfo appInfo) -> { appInfo.setName( appInfo.getName().toLowerCase()); return appInfo; })
24. Transformers • FlatMap •ConcatMap • Cast • Buffer .buffer(3) .cast(Long.class)
25. Combining List rev = Lists.reverse(apps); Observable<AppInfo> apps = Observable.from(apps); Observable<AppInfo> rApps = Observable.from(rev); Observable .merge(apps, rApps) .subscribe(observer);
26. Combining Observable<AppInfo> apps = Observable.from(list); Observable<Long> tictoc = Observable .interval(1, TimeUnit.SECONDS); private AppInfo updateTitle(AppInfo appInfo, Long time) { appInfo.setName(time + " " + appInfo.getName()); return appInfo; } Observable .zip(apps, tictoc, this::updateTitle) .subscribe(observer)
27. Defeating Android MainThread issue private Observable<List<AppInfo>> getAppsList() { return Observable .create(subscriber -> { List<AppInfo> apps = new ArrayList<>(); SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE); Type appInfoType = new TypeToken<List<AppInfo>>() { }.getType(); String serializedApps = sharedPref.getString("APPS", ""); if (!"".equals(serializedApps)) { apps = new Gson().fromJson(serializedApps, appInfoType); } subscriber.onNext(apps); subscriber.onCompleted(); }); }
28. Defeating Android MainThread issue D/StrictMode: StrictMode policy violation; ~duration=253 ms: android.os.StrictMode$StrictModeDiskReadViolation: policy=31violation=2 at android.os.StrictMode $AndroidBlockGuardPolicy.onReadFromDisk(StrictMode.java:1135) getAppsList() .subscribeOn(Schedulers.io()) .subscribe(new Observer<List<AppInfo>>() {...} Only the original thread that created a view hierarchy can touch its views.
29. Defeating Android MainThread issue D/StrictMode: StrictMode policy violation; ~duration=253 ms: android.os.StrictMode$StrictModeDiskReadViolation: policy=31violation=2 at android.os.StrictMode $AndroidBlockGuardPolicy.onReadFromDisk(StrictMode.java:1135) getAppsList() .subscribeOn(Schedulers.io()) .subscribe(new Observer<List<AppInfo>>() {...} Only the original thread that created a view hierarchy can touch its views. getAppsList() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new Observer<List<AppInfo>>() {...}
30. Defeating Android MainThread issue private Observable<AppInfo> getObservableApps(List<AppInfo> apps) { return Observable .create(subscriber -> { for (double i = 0; i < 1000000000; i++) { double y = i * i; } for (AppInfo app : apps) { subscriber.onNext(app); } subscriber.onCompleted(); }); }
31. Defeating Android MainThread issue I/Choreographer: Skipped 598 frames! The application may be doing too much work on its main thread.
32. getObservableApps(apps) .onBackpressureBuffer() .subscribeOn(Schedulers.computation()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(observer) Defeating Android MainThread issue
33. Welcome to the real world Tools • Retrolambda • Butter Knife • Lombok • Retrofit • Universal Image Loader
34. Welcome to the real world
35. Welcome to the real world public interface StackExchangeService { @GET("/2.2/users?order=desc&sort=reputation&site=stackoverflow") Observable<UsersResponse> getMostPopularSOusers(@Query("pagesize") int howmany); } public interface OpenWeatherMapService { @GET("/data/2.5/weather") Observable<WeatherResponse> getForecastByCity(@Query("q") String city); } http://www.jsonschema2pojo.org/
36. Welcome to the real world public class SeApiManager { private final StackExchangeService mStackExchangeService; public SeApiManager() { RestAdapter restAdapter = new RestAdapter.Builder() .setEndpoint("https://api.stackexchange.com") .setLogLevel(RestAdapter.LogLevel.BASIC) .build(); mStackExchangeService = restAdapter.create(StackExchangeService.class); } public Observable<List<User>> getMostPopularSOusers(int howmany) { return mStackExchangeService .getMostPopularSOusers(howmany) .map(UsersResponse::getUsers) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); } }
37. Welcome to the real world @Override protected void onCreate(Bundle savedInstanceState) { [...] mAdapter = new SoAdapter(new ArrayList<>()); mAdapter.setOpenProfileListener(this); mRecyclerView.setLayoutManager(new LinearLayoutManager(this)); mRecyclerView.setAdapter(mAdapter); mSeApiManager = new SeApiManager(); mSwipe.setOnRefreshListener(this::refreshList); refreshList(); } private void refreshList() { showRefresh(true); mSeApiManager.getMostPopularSOusers(10) .subscribe(users -> { showRefresh(false); mAdapter.updateUsers(users); }, error -> { App.L.error(error.toString()); showRefresh(false); }); }
38. Welcome to the real world public class OpenWeatherMapApiManager { @Getter private static OpenWeatherMapApiManager instance = new OpenWeatherMapApiManager(); private final OpenWeatherMapService mOpenWeatherMapService; private OpenWeatherMapApiManager() { RestAdapter restAdapter = new RestAdapter.Builder() .setEndpoint("http://api.openweathermap.org") .setLogLevel(RestAdapter.LogLevel.BASIC) .build(); mOpenWeatherMapService = restAdapter.create(OpenWeatherMapService.class); } public Observable<WeatherResponse> getForecastByCity(String city) { return mOpenWeatherMapService .getForecastByCity(city) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); } }
39. Welcome to the real world private void displayWeatherInfos(User user) { [...] OpenWeatherMapApiManager.getInstance() .getForecastByCity(city) .filter(response -> response != null) .filter(response -> response.getWeather().size() > 0) .concatMap(response -> { String url = getWeatherIconUrl(response); return loadBitmap(url); }) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe( icon -> { city_image.setImageBitmap(icon); }, error -> { App.L.error(error.toString()); }); }}
40. Welcome to the real world ViewObservable.clicks(mView) .subscribe(onClickEvent -> { checkNotNull(mProfileListener, "Must implement OpenProfileListener"); String url = user.getWebsiteUrl(); if (url != null && !url.equals("") && !url.contains("search")) { mProfileListener.open(url); } else { mProfileListener.open(user.getLink()); } });
41. Conclusions http://reactivex.io Observable sequences act like rivers: they flow. You can filter a river, you can transform a river, you can combine two rivers into one, and it will still flow. In the end, it will be the river you want it to be. Be water, my friend. - Bruce Lee