RxJava for Android explained

Three simple and naive examples of using RxJava for Android. May be useful for beginners to get started.

Also contains examples of using RxBindings, Retrolambda and SqlBrite

Transcript

1. RxJava Explained using RxAndroid, RxBindings, SqlBrite and Retrolambda Erik Hellman @ErikHellman
4. Observable and Observer private static String[] DATA = new String[] {/* some data */}; 
 public Observable<String> getData() {
 return Observable.from(DATA);
 }
 
 public void printData() {
 Subscription dataSubscription = getData()
 .subscribe(new Action1<String>() {
 @Override
 public void call(String dataItem) {
 System.out.println(dataItem);
 }
 });
 }
5. Retrolambda to the rescue! private static String[] DATA = new String[] {/* some data */}; 
 public Observable<String> getData() {
 return Observable.from(DATA);
 }
 
 public void printData() {
 Subscription dataSubscription = getData()
 .subscribe(System.out::println); }
6. Operators private static String[] DATA = new String[] {/* some data */}; 
 public Observable<String> getData() {
 return Observable.from(DATA);
 }
 
 public void printData() {
 Subscription dataSubscription = getData()
 .map(String::toLowerCase) .subscribe(System.out::println); }
7. RxJava Marble Diagrams http://rxmarbles.com/ also as an app on Google Play!
8. Progressive search from EditText
12. API call @NonNull
 private List<String> doSearch(String query) {
 // Perform network request and return result...
 }
13. Text change listener EditText searchQuery = (EditText) findViewById(R.id.search_query);
 searchQuery.addTextChangedListener(new TextWatcher() {
 @Override
 public void beforeTextChanged(CharSequence s, int start, int count, int after) { }
 
 @Override
 public void onTextChanged(CharSequence s, int start, int before, int count) { }
 
 @Override
 public void afterTextChanged(Editable editText) {
 if(editText.length() > 3) {
 mSearchHandler.obtainMessage(SEARCH_MSG, editText.toString()).sendToTarget();
 }
 }
 });
14. Throttling API calls private class SearchHandlerCallback implements Handler.Callback {
 private long mLastTimesStamp;
 
 @Override
 public boolean handleMessage(Message msg) {
 long timeStamp = SystemClock.elapsedRealtime();
 if(timeStamp > (mLastTimesStamp + QUERY_TIME_LIMIT)) {
 List<String> searchResult = doSearch((String) msg.obj);
 runOnUiThread(new Runnable() {
 @Override
 public void run() {
 // Update RecyclerView with result...
 }
 });
 mLastTimesStamp = timeStamp;
 }
 return true;
 }
 }
15. RxJava way @NonNull
 private Observable<List<String>> doSearch(String query) {
 // Perform network request and return result...
 }
16. Filter, throttle, transform, retry on error and back to main thread… subscription = RxTextView.afterTextChangeEvents(searchQuery)
 .filter(changeEvent -> changeEvent.editable().length() > 3)
 .debounce(150, MILLISECONDS)
 .switchMap(changeEvent -> doSearch(changeEvent.toString()))
 .retryWhen(new RetryOnConnectivity()) .subscribeOn(Schedulers.io())
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe(mSearchResultAdapter::setSearchResult);
17. Debounce operator
18. Loaders are horrible
19. Kitten DAO public class Kitten {
 public long id;
 public String name;
 public String photoUri;
 public String description;
 }
20. Cursor -> Kitten function public static Kitten cursorToKitten(Cursor cursor) {
 Kitten kitten = new Kitten(); 
 int idIdx = cursor.getColumnIndex(COLUMN_ID);
 kitten.id = cursor.getLong(idIdx); 
 int nameIdx = cursor.getColumnIndex(COLUMN_NAME);
 kitten.name = cursor.getString(nameIdx); 
 int photoUriIdx = cursor.getColumnIndex(COLUMN_PHOTO_URI);
 kitten.photoUri = cursor.getString(photoUriIdx); 
 int descIdx = cursor.getColumnIndex(COLUMN_DESCRIPTION);
 kitten.description = cursor.getString(descIdx); 
 return kitten;
 }
21. SqlBrite queries @Override
 protected void onResume() {
 super.onResume();
 sqlBrite = SqlBrite.create();
 BriteContentResolver resolver = sqlBrite.wrapContentProvider(getContentResolver()); 
 subscription = resolver.createQuery(KITTEN_URI, Kitten.COLUMNS, null, null, null, true)
 .mapToList(MainActivity::cursorToKitten)
 .subscribe(mAdapter::setKittens);
 }
22. Remember to unsubscribe! @Override
 protected void onPause() {
 super.onPause();
 if(!subscription.isUnsubscribed()) {
 subscription.unsubscribe();
 }
 }
23. The only EventBus you’ll ever need
24. Create a global Subject public class MyApp extends Application {
 private PublishSubject<Event> mSubject;
 
 @Override
 public void onCreate() {
 super.onCreate();
 mSubject = PublishSubject.create();
 }
 // This should be replaced with Dependency Injection public PublishSubject<Event> getSubject() {
 return mSubject;
 }
 }
25. Create an Event class public class Event {
 public long timeStamp;
 public String name;
 public String description;
 public Type type;
 
 public enum Type {
 Kitten, Dog, Rabbit
 }
 }

26. Use a simple Service @Override
 public int onStartCommand(Intent intent, int flags, int startId) {
 ((MyApp) getApplication()).getSubject().onNext(buildEvent());
 return START_NOT_STICKY;
 }
27. Subscribe to event in your Activity List<Kitten> mKittens = new LinkedList<>(); mEventSubscription = ((MyApp) getApplication()).getSubject()
 .filter(event -> event.type.equals(Event.Type.Kitten))
 .map(event -> {
 Kitten kitten = new Kitten();
 kitten.name = event.name;
 kitten.description = event.description;
 return kitten;
 })
 .subscribe(mKittens::add);
28. Don’t forget to unsubscribe! if(!mEventSubscription.isUnsubscribed()) {
 mEventSubscription.unsubscribe();
 }
29. Missed an event? public class MyApp extends Application {
 
 private BehaviorSubject<Event> mSubject;
 
 @Override
 public void onCreate() {
 super.onCreate();
 mSubject = BehaviorSubject.create();
 }
 
 public BehaviorSubject<Event> getSubject() {
 return mSubject;
 }
 }
30. BehaviorSubject
31. References • https://github.com/ReactiveX/RxJava • https://github.com/ReactiveX/RxAndroid • https://github.com/JakeWharton/RxBinding • https://github.com/square/sqlbrite • https://github.com/evant/gradle-retrolambda
32. Thank you for listening! Code samples available at github.com/ErikHellman