Stranger Streams - How to RxAndroid

My 2017 CodeMash talk on RxJava and RxAndroid.

Transcript

1. How to RxAndroid
2. Michel Yotive @myotive http://www.github.com/myotive
4. STRANGER STREAMS THE ASYNC PROBLEM ▸ Keep the main thread clean ▸ Some tools for performing background work: ▸ Handlers ▸ Loaders ▸ AsyncTask ▸ Future ▸ EventBus
5. EVALUATING TOOLS FOR ASYNC WORK ▸ Christina Lee - Intro to RxJava ▸ When do the run? ▸ How do they run? ▸ Whom do they impact? STRANGER STREAMS https://realm.io/news/intro-to-rxjava/
6. EXAMPLE: ASYNCTASK STRANGER STREAMS public class MyAsyncTask extends AsyncTask{ // you may separate this or combined to caller class. public interface AsyncResponse { void processFinish(String output); } public AsyncResponse callback = null; public MyAsyncTask(AsyncResponse callback){ this.callback = callback; } @Override protected void doInBackground(Params ...) { ... } @Override protected void onPostExecute(String result) { callback.processFinish(result); } } new MyAsyncTask(myCallback).execute();
7. EXAMPLE: ASYNCTASK STRANGER STREAMS public class MyAsyncTask extends AsyncTask{ // you may separate this or combined to caller class. public interface AsyncResponse { void processFinish(String output); } public AsyncResponse callback = null; public MyAsyncTask(AsyncResponse callback){ this.callback = callback; } @Override protected void doInBackground(Params ...) { ... } @Override protected void onPostExecute(String result) { callback.processFinish(result); } } new MyAsyncTask(myCallback).execute();
8. EXAMPLE: ASYNCTASK STRANGER STREAMS public class MyAsyncTask extends AsyncTask{ // you may separate this or combined to caller class. public interface AsyncResponse { void processFinish(String output); } public AsyncResponse callback = null; public MyAsyncTask(AsyncResponse callback){ this.callback = callback; } @Override protected void doInBackground(Params ...) { ... } @Override protected void onPostExecute(String result) { callback.processFinish(result); } } new MyAsyncTask(myCallback).execute();
9. EXAMPLE: ASYNCTASK STRANGER STREAMS public class MyAsyncTask extends AsyncTask{ // you may separate this or combined to caller class. public interface AsyncResponse { void processFinish(String output); } public AsyncResponse callback = null; public MyAsyncTask(AsyncResponse callback){ this.callback = callback; } @Override protected void doInBackground(Params ...) { ... } @Override protected void onPostExecute(String result) { callback.processFinish(result); } } new MyAsyncTask(myCallback).execute();
10. EXAMPLE: ASYNCTASK STRANGER STREAMS https://realm.io/news/intro-to-rxjava/ ▸ When does it start? ▸ Manually started ▸ How does it run? ▸ Executed as a whole and you wait for it to complete. ▸ Who is impacted? ▸ Depends…
11. IDEALS FOR DOING ASYNC WORK STRANGER STREAMS https://realm.io/news/intro-to-rxjava/ ▸ Explicit Execution ▸ Easy Thread Management ▸ Easily Composable/Transformable ▸ As few side effects as possible.
15. VISUALIZING RX STRANGER STREAMS
16. THE BIG PICTURE STRANGER STREAMS subscription = Observable.create( ... ) .operator( ... ) .operator( ... ) .operator( ... ) .subscribe( onNext(), 
 onComplete(),
 onError() 
 );
17. LAMBDA NOTATION STRANGER STREAMS new Func1<String, Integer>(){ @Override public Integer call(String s){ return s.length(); } } (String s) -> { return s.length(); } Same As
18. LAMBDA NOTATION STRANGER STREAMS new Func1<String, Integer>(){ @Override public Integer call(String s){ return s.length(); } } (String s) -> { return s.length(); } Same As
19. OBSERVABLES
20. OBSERVABLES STRANGER STREAMS ▸ Objects that emit values. ▸ OnNext( 0 … ∞ ) ▸ OnError ( 0 … 1) ▸ OnComplete (0 … 1) ▸ Stops emitting values when either OnError or OnComplete is called. ▸ Cannot call both OnError and OnComplete.
21. CREATING OBSERVABLES STRANGER STREAMS ▸ Just() ▸ Observable.Just(1) ▸ Observable.Just(1, 2) ▸ Observable.Just(1, …, 9) ▸ Observable.Just(“Hi Mom!”)
22. CREATING OBSERVABLES STRANGER STREAMS ▸ From() ▸ Observable.From(Arrays.asList(1, 2)) ▸ Observable.From(new Integer[](1, 2, 3)) ▸ Observable.From(Iterable<? extends T>)
23. CREATING OBSERVABLES STRANGER STREAMS ▸ Create<T>() ▸ Observable.Create(subscriber -> {
 subscriber.onNext(“Hello!”);
 subscriber.onNext(“From the Upside Down!”);
 subscriber.onComplete();
 }); At the beginning, you should *probably* never use this.
24. CREATING OBSERVABLES STRANGER STREAMS ▸ fromCallable() ▸ Observable.fromCallable(() -> downloadFileFromNetwork());
25. CREATING OBSERVABLES STRANGER STREAMS ▸ Observable.empty() ▸ Observable.error(<throwable>) ▸ Observable.never()
26. OBSERVABLES - POP QUIZ STRANGER STREAMS ▸ What happens if an error occurs? Observable.Create(subscriber -> { 
 try {
 Integer i = someFunctionThatMayError();
 subscriber.onNext(i);
 }
 catch(Exception e) {
 subscriber.onError(e);
 } 
 subscriber.onComplete();
 }
 );
27. OBSERVABLES STRANGER STREAMS ▸ onError and onComplete ▸ Both events end/terminate streams (Terminal Events)
28. SUBSCRIPTIONS
29. SUBSCRIPTIONS STRANGER STREAMS ▸ A method of connecting the Observer (consumer of the data) to the Observable (object emitting data). ▸ Observable.just(“Eleven”)
 .subscribe( … )
30. SUBSCRIPTIONS STRANGER STREAMS new Subscriber<T>{
 onNext(T data) { … },
 onError(Throwable e) { … },
 onComplete(){ … }
 }
31. SUBSCRIPTIONS STRANGER STREAMS String[] names = new String[] { "Eleven", "Mike", "Dustin", "Will", "Lucas" };
 
 Observable.from(names)
 .subscribe( next -> { Log.i(TAG, "onNext name: " + next); }, error -> { Log.e(TAG, "onError", error); }, () -> { Log.i(TAG, "onComplete"); } );
32. SUBSCRIPTIONS STRANGER STREAMS String[] names = new String[] { "Eleven", "Mike", "Dustin", "Will", "Lucas" };
 
 Observable.from(names)
 .subscribe( next -> { Log.i(TAG, "onNext name: " + next); }, error -> { Log.e(TAG, "onError", error); }, () -> { Log.i(TAG, "onComplete"); } );
33. SUBSCRIPTIONS STRANGER STREAMS String[] names = new String[] { "Eleven", "Mike", "Dustin", "Will", "Lucas" };
 
 Observable.from(names)
 .subscribe( next -> { Log.i(TAG, "onNext name: " + next); }, error -> { Log.e(TAG, "onError", error); }, () -> { Log.i(TAG, "onComplete"); } );
34. SUBSCRIPTIONS STRANGER STREAMS ▸ When you call “subscribe” on an Observable, you get a reference to the subscription. ▸ You may or may not need to hold onto this subscription. ▸ If you are done listening for events from the Observable, you should call “unsubscribe” on the Subscription reference.
35. SUBSCRIPTIONS STRANGER STREAMS Observable observable = … ; Subscription subscription = observable.subscribe(); 
 …
 subscription.unsubscribe();
36. OPERATORS
37. OPERATORS STRANGER STREAMS ▸ Methods for manipulating or transforming streams. ▸ RxJava comes with tons out of the box: ▸ Transforming ▸ Filtering ▸ Combining ▸ Mathematical / Aggregation ▸ More…
38. OPERATORS - MARBLE DIAGRAMS STRANGER STREAMS ▸ Visual Representation of operators and how they work.
 
 
 
 
 
 
 
 
 ▸ http://www.rxmarbles.com
39. OPERATORS - FILTER STRANGER STREAMS
40. OPERATORS - FILTER STRANGER STREAMS Observable.just("Mike", "Dustin", "Will", "Lucas", "Eleven") .filter(name -> name.equals(“Eleven")) .subscribe(next-> Toast.makeText(getContext(),next,LENGTH_LONG)
 .show() );
41. OPERATORS - FILTER STRANGER STREAMS Observable.just("Mike", "Dustin", "Will", "Lucas", "Eleven") .filter(name -> name.equals(“Eleven")) .subscribe(next-> Toast.makeText(getContext(),next,LENGTH_LONG)
 .show() );
42. OPERATORS - MAP STRANGER STREAMS
43. OPERATORS - MAP STRANGER STREAMS Observable.just("Eleven", "Mike", "Dustin", "Will", "Lucas") .map(s -> s.length()) .subscribe(integer -> 
 Toast.makeText(getContext(), 
 String.valueOf(integer), Toast.LENGTH_SHORT)
 .show()
 );
44. OPERATORS - MAP STRANGER STREAMS Observable.just("Eleven", "Mike", "Dustin", "Will", "Lucas") .map(s -> s.length()) .subscribe(integer -> 
 Toast.makeText(getContext(), 
 String.valueOf(integer), Toast.LENGTH_SHORT)
 .show()
 );
45. OPERATORS - MAP STRANGER STREAMS ▸ Question 1 - If we can convert from String to Integer, can we convert from one object to another? ▸ Yes. ▸ Question 2 - Can we convert one Observable to another? ▸ Let’s find out…
46. OPERATORS - MAP STRANGER STREAMS public interface CodeMashAPI { @GET("api/SessionsData") Observable<List<Session>> GetSessions(); @GET("api/SessionsData/{id}") Observable<Session> GetSessionById(@Path("id") UUID id); @GET("api/SpeakersData") Observable<List<Speaker>> GetSpeakers(); @GET("api/SpeakersData/{id}") Observable<SpeakerDetail> GetSpeakerDetail(@Path("id") UUID id); }
47. OPERATORS - MAP STRANGER STREAMS CodeMashAPI api = …; Observable<List<Speaker>> speakers = api.getSpeakerList(); speakers.map(speaker -> api.getSpeakerDetail(speaker.getId())) .subscribe(speakerDetail -> 
 displaySpeakerData(speakerDetail));
48. OPERATORS - MAP STRANGER STREAMS CodeMashAPI api = …; Observable<List<Speaker>> speakers = api.getSpeakerList(); speakers.map(speaker -> api.getSpeakerDetail(speaker.getId())) .subscribe(speakerDetail -> 
 displaySpeakerData(speakerDetail));
49. OPERATORS - MAP STRANGER STREAMS CodeMashAPI api = …; Observable<List<Speaker>> speakers = api.getSpeakerList(); speakers.map(speaker -> api.getSpeakerDetail(speaker.getId())) .subscribe(speakerDetail -> 
 displaySpeakerData(speakerDetail)); Observable<SpeakerDetail>
50. OPERATORS - MAP STRANGER STREAMS CodeMashAPI api = …; Observable<List<Speaker>> speakers = api.getSpeakerList(); speakers.map(speaker -> api.getSpeakerDetail(speaker.getId())) .subscribe(speakerDetail -> 
 displaySpeakerData(speakerDetail));
51. OPERATORS - MAP STRANGER STREAMS
52. OPERATORS - FLAT MAP STRANGER STREAMS CodeMashAPI api = …; Observable<List<Speaker>> speakers = api.getSpeakerList(); speakers.flatMap(speaker -> api.getSpeakerDetail(speaker.getId())) .subscribe(speakerDetail -> 
 displaySpeakerData(speakerDetail));
53. OPERATORS - FLAT MAP STRANGER STREAMS CodeMashAPI api = …; Observable<List<Speaker>> speakers = api.getSpeakerList(); speakers.flatMap(speaker -> api.getSpeakerDetail(speaker.getId())) .subscribe(speakerDetail -> 
 displaySpeakerData(speakerDetail)); SpeakerDetail
54. OPERATORS - MAP VS FLAT MAP STRANGER STREAMS ▸ Map converts from on type to another. ▸ Flat Map transforms an observable from one type to an observable of another type.
55. OPERATORS - ZIP STRANGER STREAMS
56. OPERATORS - ZIP STRANGER STREAMS GitHubApi api = getGitHubApi(); Observable<User> userObservable = 
 api.getUser(loginName);
 
 Observable<List<Events>> eventsObservable = 
 api.listEvents(loginName);
57. OPERATORS - ZIP STRANGER STREAMS GitHubApi api = getGitHubApi(); Observable<User> userObservable = 
 api.getUser(loginName);
 
 Observable<List<Events>> eventsObservable = 
 api.listEvents(loginName);
58. OPERATORS - ZIP STRANGER STREAMS userObservable.subscribe (next -> eventsObservable.subscribe(next -> … ) );
59. OPERATORS - ZIP STRANGER STREAMS Observable<User> userObservable = … ; Observable<List<Events>> eventsObservable = … ; Observable<UserEvents> combined = 
 Observable.zip(
 userObservable, eventsObservable, (user, events) -> new UserEvents(user, events); );
60. OPERATORS - ZIP STRANGER STREAMS Observable<User> userObservable = … ; Observable<List<Events>> eventsObservable = … ; Observable<UserEvents> combined = 
 Observable.zip(
 userObservable, eventsObservable, (user, events) -> new UserEvents(user, events); );
61. OPERATORS - ZIP STRANGER STREAMS Observable<User> userObservable = … ; Observable<List<Events>> eventsObservable = … ; Observable<UserEvents> combined = 
 Observable.zip(
 userObservable, eventsObservable, (user, events) -> new UserEvents(user, events); ); combined.subscribe(userEventObj ->
 // do something with UserEvents object );
62. DEMO
63. SCHEDULERS
64. SCHEDULERS STRANGER STREAMS ▸ Mechanism for scheduling/managing threads. ▸ Govern the transition between threads. ▸ Two operators: ▸ subscribeOn ▸ observeOn
65. SCHEDULERS - SUBSCRIBE ON STRANGER STREAMS ▸ Specifies which thread the Observable will operate. ▸ If not specified, defaults to the thread on which the Observable was created. ▸ Declared only once. ▸ If used multiple times, first usage wins.
66. SCHEDULERS - OBSERVE ON STRANGER STREAMS ▸ Specifies which thread the Observer will operate. ▸ If not specified, defaults to the thread on which subscribeOn was assigned ▸ Declared as many times as needed ▸ If used multiple times, affects downstream operations.
67. SCHEDULERS STRANGER STREAMS subscription = Observable
 .fromCallable( ()-> expensiveMethod() ) .subscribeOn( Schedulers.io() ) .observeOn( Schedulers.newThread() ) .subscribe( onNext(),
 onError(),
 onComplete()
 );
68. SCHEDULERS STRANGER STREAMS ▸ Schedulers.io() ▸ Schedulers.newThread() ▸ Schedulers.computation() ▸ Schedulers.immediate() ▸ Schedulers.trampoline()
69. SCHEDULERS STRANGER STREAMS createSpeakerObservable() .subscribeOn(Schedulers.io()) .observeOn(<Android Main UI Thread>) .subscribe(new Subscriber<List<Speaker>>() { @Override public void onCompleted() { } @Override public void onError(Throwable e) { Log.e(TAG, "Error calling CodeMash api", e); } @Override public void onNext(List<Speaker> speakers) { Toast.makeText(getContext(), "Number of speakers: " + String.valueOf(speakers.size()), Toast.LENGTH_LONG).show(); } });
70. SCHEDULERS STRANGER STREAMS createSpeakerObservable() .subscribeOn(Schedulers.io()) .observeOn(<Android Main UI Thread>) .subscribe(new Subscriber<List<Speaker>>() { @Override public void onCompleted() { } @Override public void onError(Throwable e) { Log.e(TAG, "Error calling CodeMash api", e); } @Override public void onNext(List<Speaker> speakers) { Toast.makeText(getContext(), "Number of speakers: " + String.valueOf(speakers.size()), Toast.LENGTH_LONG).show(); } });
71. RXANDROID
72. RXANDROID STRANGER STREAMS ▸ An extension to RxJava built just for Android. ▸ Adds the bare minimum classes needed to do RxJava on Android. ▸ AndroidSchedulers.mainThread()
73. RXANDROID STRANGER STREAMS dependencies { … compile 'io.reactivex:rxandroid:1.2.1' compile ‘io.reactivex:rxjava:1.1.6' 
 (optional) compile ‘io.reactivex:rxjava-math:1.0.0' 
 … }
74. RXANDROID - CAVEATS STRANGER STREAMS ▸ Subscriptions and the Android lifecycle ▸ How do we continue a subscription on configuration change? ▸ Be mindful if you have a long running operation and your activity/fragment is terminated.
75. RXANDROID - CAVEATS STRANGER STREAMS public class MainActivity extends AppCompatActivity { private Subscription subscription; private Observable observable; ... @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ... observable = <create observable here>; } @Override protected void onResume() { super.onResume(); subscription = observable.subscribe(); } @Override protected void onStop() { super.onDestroy(); subscription.unsubscribe(); } }
76. RXANDROID - CAVEATS STRANGER STREAMS public class MainActivity extends AppCompatActivity { private Subscription subscription; private Observable observable; ... @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ... observable = <create observable here>; } @Override protected void onResume() { super.onResume(); subscription = observable.subscribe(); } @Override protected void onStop() { super.onDestroy(); subscription.unsubscribe(); } }
77. RXANDROID - CAVEATS STRANGER STREAMS private CompositeSubscription compositeSubscription; private Observable observable1, observable2, observable3; ... @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); observable1 = <create observable here>; observable2 = <create observable here>; observable3 = <create observable here>; } @Override protected void onResume() { super.onResume(); compositeSubscription.add(observable1.subscribe(); compositeSubscription.add(observable2.subscribe(); compositeSubscription.add(observable3.subscribe(); } @Override protected void onStop() { super.onStop(); compositeSubscription.unsubscribe(); }
78. RXANDROID - CAVEATS STRANGER STREAMS private CompositeSubscription compositeSubscription; private Observable observable1, observable2, observable3; ... @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); observable1 = <create observable here>; observable2 = <create observable here>; observable3 = <create observable here>; } @Override protected void onResume() { super.onResume(); compositeSubscription.add(observable1.subscribe(); compositeSubscription.add(observable2.subscribe(); compositeSubscription.add(observable3.subscribe(); } @Override protected void onStop() { super.onStop(); compositeSubscription.unsubscribe(); }
79. RXANDROID LIBRARIES
80. RXANDROID - RXBINDING STRANGER STREAMS ▸ Adds bindings to Android UI widgets. RxTextView.textChanges(<view>)
 .map( c -> … )
 .subscribe( i -> … )
81. RXANDROID - RXLIFECYCLE STRANGER STREAMS ▸ Adds bindings to respond to the Android Lifecycle myObservable.compose(bindUntilEvent(ActivityEvent.Destroy))
 .subscribe( … ) (Note: Fragments/Activities must extend RxActivity/
 RxAppCompatActivity or RxFragment)
82. DEMO
83. CLOSING THOUGHTS
84. CLOSING THOUGHTS STRANGER STREAMS ▸ Observables are immutable z Observable<String> obs = Observable.just(“Hello”); obs.map(s -> s.length()); obs.subscribe( i -> Log.i(TAG, String.valueOf(i)); versus Observable.just(“Hello”) .map(s -> s.length()) .subscribe(i -> Log.i(TAG, String.valueOf(i));
85. CLOSING THOUGHTS STRANGER STREAMS ▸ Observables are immutable z Observable<String> obs = Observable.just(“Hello”); obs.map(s -> s.length()); obs.subscribe( i -> Log.i(TAG, String.valueOf(i)); versus Observable.just(“Hello”) .map(s -> s.length()) .subscribe(i -> Log.i(TAG, String.valueOf(i));
86. CLOSING THOUGHTS STRANGER STREAMS ▸ Observables are immutable z Observable<String> obs1 = Observable.just(“Hello”); Observable<Integer> obs2 = obs1.map(s -> s.length()); obs2.subscribe( i -> Log.i(TAG, String.valueOf(i));
87. CLOSING THOUGHTS STRANGER STREAMS ▸ Observables are immutable z Observable<String> obs1 = Observable.just(“Hello”); Observable<Integer> obs2 = obs1.map(s -> s.length()); obs2.subscribe( i -> Log.i(TAG, String.valueOf(i));
88. CLOSING THOUGHTS STRANGER STREAMS ▸ Subjects z
89. CLOSING THOUGHTS STRANGER STREAMS ▸ RxJava 2.0 ▸ Released October 29th ▸ New Type: Flowable ▸ Use cases: https://goo.gl/HzLFfm ▸ Nulls are no longer permitted. z Observable.just(null); //don’t do this
90. CLOSING THOUGHTS STRANGER STREAMS ▸ Helpful Libraries that aid in reactive development on Android ▸ Rx Cache ▸ Rx Preferences ▸ RxLoader ▸ RxPermissions ▸ Retrofit ▸ Realm z
91. QUESTIONS? https://github.com/myotive