RxJava on Android

Describing just how RxJava simplifies your code and your concurrency handling in Android applications.

Transcript

1. RxJava on Android Jernej Virag @jernejv
2. Let’s talk about pain. Jernej Virag @jernejv
3. Loader, AsyncTask, Executor, Main thread execution oh my! Jernej Virag @jernejv
4. RxJava dependencies {
 compile 'io.reactivex:rxjava:1.0.8'
 compile 'io.reactivex:rxandroid:0.24.0'
 }
5. RxJava dependencies {
 compile 'io.reactivex:rxjava:1.0.8'
 compile 'io.reactivex:rxandroid:0.24.0'
 }
6. Observable<> Jernej Virag @jernejv
7. Observable<> @GET("/api/search/shares/")
 Observable<RestSearchResults> search(@Query("f") String from,
 @Query("t") String to); @GET("/api/search/shares/")
 void search(@Query("f") String from,
 @Query("t") String to, 
 Callback<RestSearchResults> callback); @GET("/api/search/shares/")
 RestSearchResults search(@Query("f") String from,
 @Query("t") String to); Synchronous interface Callback interface Reactive interface Sync Async TBD
8. Observable<> @GET("/api/search/shares/")
 Observable<RestSearchResults> search(@Query("f") String from,
 @Query("t") String to); @GET("/api/search/shares/")
 void search(@Query("f") String from,
 @Query("t") String to, 
 Callback<RestSearchResults> callback); @GET("/api/search/shares/")
 RestSearchResults search(@Query("f") String from,
 @Query("t") String to); Synchronous interface Callback interface Reactive interface Sync Async TBD
9. Observable<> @GET("/api/search/shares/")
 Observable<RestSearchResults> search(@Query("f") String from,
 @Query("t") String to); @GET("/api/search/shares/")
 void search(@Query("f") String from,
 @Query("t") String to, 
 Callback<RestSearchResults> callback); @GET("/api/search/shares/")
 RestSearchResults search(@Query("f") String from,
 @Query("t") String to); Synchronous interface Callback interface Reactive interface Sync Async TBD (!)
10. Observables can be chained Jernej Virag @jernejv
11. Observable<> ApiClient.getAdapter().search(fromCity, toCity, dateString)
 .flatMap(restSearchResults -> Observable.from(restSearchResults.results))
 .filter(restRide -> restRide.date.before(Calendar.getInstance()))
 .map(restRide -> {
 // Localize
 restRide.setLocalizedFrom(context);
 restRide.setLocalizedTo(context);
 return restRide;
 })
 .toSortedList()
12. A few operators • map() - Object in stream to another single object • flatMap() - Object in stream to one or more objects • buffer(), debounce() - Congestion control • filter() - drop objects in stream according to predicate • take(), skip(), single(), first() - get only certain number of objects • https://github.com/ReactiveX/RxJava/wiki/Alphabetical-List-of-Observable-Operators
13. Making observables • Observable.just( obj ) - single object to observable • Observable.defer( function ) - delay execution of fun. • Observable.from( collection ) - turn collection into observable stream • Observable.create( custom source ) - create a stream by calling onNext() / onError() / onComplete Jernej Virag @jernejv
14. Observable<> ApiClient.getAdapter().search(fromCity, toCity, dateString)
 .flatMap(restSearchResults -> Observable.from(restSearchResults.results))
 .filter(restRide -> restRide.date.before(Calendar.getInstance()))
 .map(restRide -> {
 // Localize
 restRide.setLocalizedFrom(context);
 restRide.setLocalizedTo(context);
 return restRide;
 })
 .toSortedList()
15. Subscriber Jernej Virag @jernejv
16. Subscriber ApiClient.getAdapter().search(fromCity, toCity, dateString) …
 .toSortedList() .subscribe(new Subscriber<List<RestRide>>() {
 @Override
 public void onCompleted() { // Nothing to be done }
 @Override
 public void onError(Throwable e) {
 ViewUtils.showErrorMessage(context, "Could not find results…”);
 }
 @Override
 public void onNext(List<RestRide> restRides) {
 resultList.setAdapter(new SearchResultsAdapter(restRides));
 }
 });
17. Subscriber ApiClient.getAdapter().search(fromCity, toCity, dateString) …
 .toSortedList() .subscribe(new Subscriber<List<RestRide>>() {
 @Override
 public void onCompleted() { // Nothing to be done }
 @Override
 public void onError(Throwable e) {
 ViewUtils.showErrorMessage(context, "Could not find results…”);
 }
 @Override
 public void onNext(List<RestRide> restRides) {
 resultList.setAdapter(new SearchResultsAdapter(restRides));
 }
 });
18. Subscriber ApiClient.getAdapter().search(fromCity, toCity, dateString) …
 .toSortedList() .subscribe(new Subscriber<List<RestRide>>() {
 @Override
 public void onCompleted() { // Nothing to be done }
 @Override
 public void onError(Throwable e) {
 ViewUtils.showErrorMessage(context, "Could not find results…”);
 }
 @Override
 public void onNext(List<RestRide> restRides) {
 resultList.setAdapter(new SearchResultsAdapter(restRides));
 }
 });
19. Subscriber ApiClient.getAdapter().search(fromCity, toCity, dateString) …
 .toSortedList() .subscribe(new Subscriber<List<RestRide>>() {
 @Override
 public void onCompleted() { // Nothing to be done }
 @Override
 public void onError(Throwable e) {
 ViewUtils.showErrorMessage(context, "Could not find results…”);
 }
 @Override
 public void onNext(List<RestRide> restRides) {
 resultList.setAdapter(new SearchResultsAdapter(restRides));
 }
 });
20. Concurrency Jernej Virag @jernejv
21. Concurrency ApiClient.getAdapter().search(fromCity, toCity, dateString) …
 .toSortedList()
 .subscribeOn(Schedulers.io())
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe(…); Jernej Virag @jernejv
22. Concurrency • Schedulers.newThread() • Schedulers.io() • Schedulers.computation() • AndroidSchedulers.mainThread() Jernej Virag @jernejv
23. More examples Jernej Virag @jernejv
24. More examples RxLocationProvider.getCurrentLocation()
 .map(location -> Geocoder.getAddressForLocation())
 .map(address -> ApiClient.getBitmapForCity(address))
 .onErrorReturn(throwable -> placeholderBitmap)
 .defaultIfEmpty(placeholderBitmap)
 
 .subscribeOn(Schedulers.io())
 .observeOn(AndroidSchedulers.mainThread())
 
 .subscribe(bitmap -> {
 headerImageView.setImageDrawable( new FadeInDrawable(bitmap));
 });
25. More examples Observable<List<SearchResult>> groupedResults = TextProvider.findStringInDocument(getContext(), document, searchString, configuration.getSnippetLength())
 .map(searchResult -> {
 searchResult.setHighlightColor(configuration.getHighlightColor());
 return searchResult;
 }
 })
 .buffer(300, TimeUnit.MILLISECONDS)
 .onBackpressureBuffer() … groupedResults.debounce() .observeOn(AndroidSchedulers.mainThread())
 .subscribe(new Subscriber<List<SearchResult>>() {
 @Override
 public void onCompleted() {
 String searchCompleted = getResources().getString(R.string.pspdf__search_complete);
 String matchesFound = getResources().getQuantityString(R.plurals.pspdf__search_results_found, adapter.getCount(), adapter.getCount());
 SpannableString str = new SpannableString(searchCompleted + "\n" + matchesFound);
 footer.setText(str);
 footer.setVisibility(View.VISIBLE);
 throbber.setVisibility(View.INVISIBLE);
 }
 
 @Override
 public void onError(Throwable throwable) { footer.setText(“Results could not be retrieved.”); 
 }
 
 @Override
 public void onNext(List<SearchResult> searchResults) {
 adapter.addResults(searchResults);
 EventBus.getDefault().post(new Events.NewSearchResults(searchResults));
 }
 });
26. The downsides Jernej Virag @jernejv
27. The downsides • On Java 6 it requires creation of A LOT of anonymous classes • It’s generally not easy on GC • It’s very easy to leak references in the anon. classes • Use RxAndroid bind() calls to help you • It’s a rather large dependency Jernej Virag @jernejv
28. Where to start • RxJava GitHub + Wiki Documentation
 https://github.com/ReactiveX/RxJava • Grokking RxJava / Android, Parts 1-4
 http://blog.danlew.net/2014/09/15/grokking-rxjava-part-1/ • Fragmented Podcast Episode 3/4
 https://player.fm/series/fragmented-67211/episode-3-rxjava-with-dan-lew-part-1 
 https://player.fm/series/fragmented-67211/episode-4-rxjava-with-dan-lew-part-2 Jernej Virag @jernejv
29. Neat stuff • Retrofit
 https://square.github.io/retrofit/ • SqlBrite
 https://github.com/square/sqlbrite • Reactive Location
 https://github.com/mcharmas/Android-ReactiveLocation Jernej Virag @jernejv
30. ?
 
 @jernejv
 http://www.virag.si (when it’s back)