Simplify Your Code with Rx

Show how you can simplify your class design with Rx (reactive extensions), with implementation in RxJava.

Transcript

1. Simplify Your Code with Rx DroidCon, March 18 2016 Ferry Tanu - @Yahoo
2. ▪ What is VideoSDK? ▪ What is Rx? ▪ Show me the code ▪ Q&A Agenda 2
3. What is VideoSDK?
4. What is VideoSDK? ▪ A video player wrapper ▪ Purpose: to make it easier for app to integrate with video players ▪ Manage between ads and content ▪ Components: › Remote API call (aka HTTP call) › Instrumentation › UI/UX according to company brand › Error handling
5. What is VideoSDK? ▪ A video player wrapper ▪ Purpose: to make it easier for app to integrate with video players ▪ Manage between ads and content ▪ Components: › Remote API call (aka HTTP call) › Instrumentation › UI/UX according to company brand › Error handling
6. Problem: • Player manages the clock lifecycle • Clock implements player listener → ugly! • Clock need to maintain state • Frozen detection (event) depends on player state • Update the seekbar UI to reflect playback position • Detect Inactivity
7. Video has to play in X seconds Problem: • Timer is managed by multi party
8. The birth of the god object god object media player playback listener timer instrume ntation clock api service ads ui
9. Can we simplify?
10. The Observer pattern done right (reactivex.io) ReactiveX is a combination of the best ideas from the Observer pattern, the Iterator pattern, and functional programming Reactive Extensions (Rx)
11. Observer Producer Consumer Pull Producer Consumer Push subscribe
12. Iterator Multi value onNext() onComplete()
13. Imperative Integer[] list= new Integer[]{1, 2, 3, 4, 5}; int acc = 0; for ( int i = 0; i < list.length; i++ ) { acc = acc + 3 * list[i]; } Functional Programming Build Complexity out of Simplicity using Composition RxJava sumInteger( from(list) .map((num) -> { 3 * num }) ).subscribe(/* do with the total */); Haskell sum (map (3*) list)
14. Observable.create(...) .operator(...) .operator(...) .subscribe( onNextAction(), [onErrorAction(), [onCompleteAction()]] );
15. Let’s see the code!
16. Observable => Topic
17. Objective player clock subscribe playing paused ui controller changed frozen emit
18. Create Observable MediaPlayer mObservableMediaPlayer = Observable.create(new PlayerEventOnSubscribe(mediaPlayer)).publish(); class PlayerEventOnSubscribe implements Observable.OnSubscribe<Integer> { @Override public void call(final Subscriber<? super Integer> subscriber) { PlayerEventListener listener = new PlayerEventListener() { @Override public void onPlaying() { onNext(subscriber, PLAYING); } @Override public void onPaused() { onNext(subscriber,PAUSED); } @Override public void onReleased() { if (!subscriber.isUnsubscribed()) { onNext(subscriber, RELEASED); subscriber.unsubscribe(); } } }; player.setPlayerEventListener(listener); subscriber.add(new MainThreadSubscription() { @Override protected void onUnsubscribe() { player.setPlayerEventListener(null); } }); } void onNext(Subscriber<? super Integer> subscriber, int state) { if (!subscriber.isUnsubscribed()) { subscriber.onNext(state); } } Unsubscribe
19. Observable Media Player interface PlayerEventListener { void onPrepared(); void onPlaying(); void onPaused(); .... } Observable<Integer> prepared() { return mMediaPlayerObservable.filter(equalTo(PREPARED)); } Observable<Integer> playing() { return mMediaPlayerObservable.filter(equalTo(PLAYING)); } Observable<Integer> paused() { return mMediaPlayerObservable.filter(equalTo(PAUSED)); }
20. Create Observable Playback Clock mClockObservable = Observable.interval(1, SECONDS) .map((aLong) -> mediaPlayer.getCurrentPosition()) .publish(); map time to playback position Timer with interval 1 second
21. Manage Clock Lifecycle // clock start when player start to play playing() .subscribe((i) -> { mSubscription = mClockObservable.connect(); }, RxLog.e(TAG, "ouch!!")); // stop when player is pause or complete or released Observable.merge(paused(), playComplete(), released()) .subscribe((integer) -> { mSubscription.unsubscribe(); }, RxLog.e(TAG, "ouch!!")); player clock subscribe playing paused / complete/ released
22. Observable Playback Clock clock ui controller changed frozen
23. Topic are composable changed frozen map time to playback position distinct Calculate frozen time Filter >= gracePeriod Timer with interval 1 second
24. Observable Playback Clock mClockObservable = Observable.interval(1, SECONDS) .map((aLong) -> mediaPlayer.getCurrentPosition()) .publish(); Observable<Long> changed() { return mClockObservable .distinctUntilChanged(); } Observable<Integer> frozen(final int gracePeriod) { return mClockObservable .map(calculateFrozenTime()) .filter((frozenTime) -> frozenTime >= gracePeriod); } Map the clock value to playback position Only emit when position changed changed() .subscribe(()-> {/*update seekbar position*/}); frozen() .subscribe(()-> {/*reload player*/}); Emit when frozen for more than grace period
25. Detect Inactivity Observable<Integer> frozen(final int gracePeriod) { return mClockObservable .map(calculateFrozenTime()) .filter((frozenTime) -> frozenTime >= gracePeriod }); Func1<Long, Integer> calculateFrozenTime() { return new Func1<Long, Integer>() { Long lastPlayTime = 0L; Integer frozenTime = 0; @Override public Integer call(Long currentPlayTime) { if (!lastPlayTime.equals(currentPlayTime)) { lastPlayTime = currentPlayTime; frozenTime = 0; } else { frozenTime++; } return frozenTime; } }; }
26. One more time - the beauty of composition
27. Make sure it plays in X seconds prepared release first timeout Do something Do nothing
28. Start to play or released void shouldStartPlayIn(long timeoutS, Action1<Throwable> actionWhenFailed) { Observable.merge(prepared(), released()) prepared release
29. Either start to play or released void shouldStartPlayIn(long timeoutS, Action1<Throwable> actionWhenFailed) { Observable.merge(prepared(), released()) .first() prepared release first
30. Either start to play or released in X seconds void shouldStartPlayIn(long timeoutS, Action1<Throwable> actionWhenFailed) { Observable.merge(prepared(), released()) .first() .timeout(timeoutMs, SECONDS) prepared release first timeout
31. Either start to play or released in X seconds -> action void shouldStartPlayIn(long timeoutS, Action1<Throwable> actionWhenFailed) { Observable.merge(prepared(), released()) .first() .timeout(timeoutMs, SECONDS) .doOnError(RxLog.e(TAG, "Video not playing in " + timeoutS)) .observeOn(AndroidSchedulers.mainThread()) .subscribe((i) -> {/* no action if the condition satisfied*/}, actionWhenFailed); } prepared release first timeout Do something Do nothing
32. Wow, that looks simple!
33. Questions?
34. Thank You