Build Your Custom Observable/Operator

In this talk, I am explaining how to model a stream and how to implement custom observable/operator, taking RxNearby (https://github.com/hkurokawa/RxNearby) as an example.

There are some pitfalls in developing your own Observable or Operator and this talk covers that.

Links:
- Pitfalls of operator implementations (part 1)
http://akarnokd.blogspot.jp/2015/05/pitfalls-of-operator-implementations.html

Transcript

1. Build Your Custom Observable/Operator Hiroshi Kurokawa (@hydrakecat)
2. Reference • The Slides
 https://speakerdeck.com/hkurokawa/operator • RxNearby
 https://github.com/hkurokawa/rxnearby
3. When you need custom Observable/Operator? // Retrofit service.users() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(users -> { adapter.setItems(users); }); // RxBinding RxView.scrollChangeEvents(listView) .subscribe(event -> { int dy = event.scrollY() - event.oldScrollY(); });
4. When you need custom Observable/Operator? // Retrofit service.users() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(users -> { adapter.setItems(users); }); // RxBinding RxView.scrollChangeEvents(listView) .subscribe(event -> { int dy = event.scrollY() - event.oldScrollY(); }); When you want to model something as a stream!
5. When you need custom Observable/Operator? // Retrofit service.users() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(users -> { adapter.setItems(users); }); // RxBinding RxView.scrollChangeEvents(listView) .subscribe(event -> { int dy = event.scrollY() - event.oldScrollY(); }); When you want to model something as a stream!
6. When you need custom Observable/Operator? // Retrofit service.users() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(users -> { adapter.setItems(users); }); // RxBinding RxView.scrollChangeEvents(listView) .subscribe(event -> { int dy = event.scrollY() - event.oldScrollY(); }); When you want to model something as a stream!
7. When you need custom Observable/Operator? // Retrofit service.users() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(users -> { adapter.setItems(users); }); // RxBinding RxView.scrollChangeEvents(listView) .subscribe(event -> { int dy = event.scrollY() - event.oldScrollY(); }); When you want to model something as a stream!
8. (http://slides.com/robwormald/everything-is-a-stream#/)
9. Nearby Messaging API • Subscribe messages from other Android devices
 • Publish messages to other Android devices
10. Nearby Messaging API • Subscribe messages from other Android devices
 Modelled as Observable • Publish messages to other Android devices
11. Nearby Messaging API • Subscribe messages from other Android devices
 Modelled as Observable • Publish messages to other Android devices
 Modelled as Operator Operator
12. Nearby Messaging API • Subscribe messages from other Android devices
 Modelled as Observable • Publish messages to other Android devices
 Modelled as Operator 9JCV!1RGTCVQT!
13. Why Operator? • When and how do you want a message is published? - Publish when user clicks a button - Publish when the app loads data from local DB or a server • Why don’t you handle such trigger as an Observable?
14. (http://slides.com/robwormald/everything-is-a-stream#/)
15. Publishing a message Trigger Events (ex. button click) Message Published Events Operator
16. Publishing a message
17. Publishing a message
18. Publishing a message
19. Publishing a message
20. Publishing a message
21. What is Observable? What is Operator? • Observable is something to emit a sequence of events to the given Subscriber
22. What is Observable? What is Operator? • Observable is something to emit a sequence of events to the given Subscriber - From implementation points of view, we create an OnSubscribe instead of Observable itself Observable.create(new OnSubscribe() { … })
23. What is Observable? What is Operator? • Observable is something to emit a sequence of events to the given Subscriber - From implementation points of view, we create an OnSubscribe instead of Observable itself • Operator converts an Observable to another Observable Observable.create(new OnSubscribe() { … })
24. What is Observable? What is Operator? • Observable is something to emit a sequence of events to the given Subscriber - From implementation points of view, we create an OnSubscribe instead of Observable itself • Operator converts an Observable to another Observable - From implementation points of view, we implement a method to return a subscriber from the given subscriber Observable.create(new OnSubscribe() { … })
25. What is Observable? What is Operator? • Observable is something to emit a sequence of events to the given Subscriber - From implementation points of view, we create an OnSubscribe instead of Observable itself • Operator converts an Observable to another Observable - From implementation points of view, we implement a method to return a subscriber from the given subscriber Observable.create(new OnSubscribe() { … }) Subscriber is the core of RxJava
26. OnSubscribe Example:
 range() @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(i); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
27. How OnSubscribe works Observable.range(1, 5) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, “Completed.") );
28. How OnSubscribe works Observable.range(1, 5) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, “Completed.") );
29. How OnSubscribe works Observable.range(1, 5) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, “Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(i); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
30. How OnSubscribe works Observable.range(1, 5) .subscribe( i -> Log.i(TAG, "Output: " + 1), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, “Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(1); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
31. How OnSubscribe works Observable.range(1, 5) .subscribe( i -> Log.i(TAG, "Output: " + 2), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, “Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(2); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
32. How OnSubscribe works Observable.range(1, 5) .subscribe( i -> Log.i(TAG, "Output: " + 3), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, “Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(3); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
33. How OnSubscribe works Observable.range(1, 5) .subscribe( i -> Log.i(TAG, "Output: " + 4), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, “Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(4); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
34. How OnSubscribe works Observable.range(1, 5) .subscribe( i -> Log.i(TAG, "Output: " + 5), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, “Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(5); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
35. How OnSubscribe works Observable.range(1, 5) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, “Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(i); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
36. Operator Example: map() @Override public Subscriber<? super Integer> call(Subscriber<? super Integer> child) { return new Subscriber<Integer>() { @Override public void onCompleted() { child.onCompleted(); } @Override public void onError(Throwable e) { child.onError(e); } @Override public void onNext(Integer i) { try { child.onNext(transformer.call(i)); } catch (Throwable e) { Exceptions.throwOrReport(e, this, i); } } }; }
37. Operator Example: map() @Override public Subscriber<? super Integer> call(Subscriber<? super Integer> child) { return new Subscriber<Integer>() { @Override public void onCompleted() { child.onCompleted(); } @Override public void onError(Throwable e) { child.onError(e); } @Override public void onNext(Integer i) { try { child.onNext(transformer.call(i)); } catch (Throwable e) { Exceptions.throwOrReport(e, this, i); } } }; }
38. How Operator works Observable.range(1, 5) .map(i -> i * 2) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") );
39. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") );
40. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") );
41. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") );
42. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); public final <Integer> Observable<Integer> lift(final OperatorMap operator) { return new Observable<>(new Observable.OnSubscribe<Integer>() { @Override public void call(Subscriber<? super Integer> o) { // new Subscriber created and being subscribed with so 'onStart' it Subscriber<? super Integer> st = operator.call(o); st.onStart(); onSubscribe.call(st); } }); }
43. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); public final <Integer> Observable<Integer> lift(final OperatorMap operator) { return new Observable<>(new Observable.OnSubscribe<Integer>() { @Override public void call(Subscriber<? super Integer> o) { // new Subscriber created and being subscribed with so 'onStart' it Subscriber<? super Integer> st = operator.call(o); st.onStart(); onSubscribe.call(st); } }); }
44. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); Subscriber<? super Integer> st = operator.call(o); st.onStart(); onSubscribe.call(st);
45. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); Subscriber<? super Integer> st = operator.call(o); st.onStart(); onSubscribe.call(st); child subscriber
46. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); Subscriber<? super Integer> st = operator.call(o); st.onStart(); onSubscribe.call(st); child subscriber new subscriber
47. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); Subscriber<? super Integer> st = operator.call(o); st.onStart(); onSubscribe.call(st);
48. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); Subscriber<? super Integer> st = operator.call(o); st.onStart(); onSubscribe.call(st);
49. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(i); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
50. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { for (int i = start; i < start + count; i++) { if (subscriber.isUnsubscribed()) { return; } subscriber.onNext(i); } if (!subscriber.isUnsubscribed()) { subscriber.onCompleted(); } }
51. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { … subscriber.onNext(i); … }
52. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { … subscriber.onNext(i); … } @Override public void onNext(Integer i) { child.onNext(transformer.call(i)); }
53. How Operator works Observable.range(1, 5) .lift(new OperatorMap(i -> i*2)) .subscribe( i -> Log.i(TAG, "Output: " + i), throwable -> Log.e(TAG, "Error: ", throwable), () -> Log.i(TAG, "Completed.") ); @Override public void call(Subscriber<? super Integer> subscriber) { … subscriber.onNext(i); … } @Override public void onNext(Integer i) { child.onNext(transformer.call(i)); }
54. How Operator works • Operator defines how to create a new parent subscriber from the given child subscriber • When subscribed, it invokes its onSubscribe with that new parent subscriber • When the operators are chained, the onSubscribe invocations are also chained from child to parent • The onNext invocations are chained from parent to child
55. Nearby Messages API • Subscribe messages from other Android devices
 Modelled as Observable • Publish messages to other Android devices
 Modelled as Operator
56. Nearby Messages API • Subscribe messages from other Android devices
 Modelled as Observable • Publish messages to other Android devices
 Modelled as Operator
57. MessageSubscribeOnSubscribe Nearby.Messages .subscribe(apiClient, listener) .setResultCallback(callback); apiClient.connect();
58. MessageSubscribeOnSubscribe Nearby.Messages .subscribe(apiClient, listener) .setResultCallback(callback); apiClient.connect();
59. MessageSubscribeOnSubscribe Nearby.Messages .subscribe(apiClient, new MessageListener() { @Override public void onFound(Message message) { if (!subscriber.isUnsubscribed()) { subscriber.onNext(message); } } }) .setResultCallback(callback); apiClient.connect();
60. MessageSubscribeOnSubscribe Nearby.Messages .subscribe(apiClient, new MessageListener() { @Override public void onFound(Message message) { if (!subscriber.isUnsubscribed()) { subscriber.onNext(message); } } }) .setResultCallback(status -> { if (!status.isSuccess() && !subscriber.isUnsubscribed()) { subscriber.onError(new ApiStatusException(status)); } }); apiClient.connect();
61. MessageSubscribeOnSubscribe apiClient.unsubscribe(listener, callback); apiClient.disconnect();
62. subscriber.add(new Subscription() { @Override public void unsubscribe() { } @Override public boolean isUnsubscribed() { return apiClient.isConnected(); } }); MessageSubscribeOnSubscribe apiClient.unsubscribe(listener, callback); apiClient.disconnect();
63. MessageSubscribeOnSubscribe @Override public void call(final Subscriber<? super Message> subscriber) { final MessageListener listener = new MessageListener() { @Override public void onFound(Message message) { if (!subscriber.isUnsubscribed()) { subscriber.onNext(message); } } }; final ApiClientWrapper.ResultHandler handler = new ApiClientWrapper.ResultHandler() { @Override public void onSuccess() { } @Override public void onError(Status status) { if (!subscriber.isUnsubscribed()) { subscriber.onError(new ApiStatusException(status)); } } }; apiClient.subscribe(listener, handler); subscriber.add(new Subscription() { @Override public void unsubscribe() { apiClient.unsubscribe(listener, handler); apiClient.disconnect(); } @Override public boolean isUnsubscribed() { return apiClient.isConnected(); } }); apiClient.connect(); }
64. Takeaways • Basically do not do anything until it is subscribed • Make sure any resources is released when unsubscribed • To make it back-pressure aware, use Subscriber#setProducer() • The thread of OnSubscribe#call() can be specified with subscribeOn() operator • There is a contract. See http://reactivex.io/ documentation/contract.html
65. Nearby Messages API • Subscribe messages from other Android devices
 Modelled as Observable • Publish messages to other Android devices
 Modelled as Operator
66. MessagePublishOperator @Override public Subscriber<? super Message> call(Subscriber<? super PublishResult> child) { final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } @Override public void onCompleted() { child.onCompleted(); } @Override public void onError(Throwable e) { child.onError(e); } }; }
67. MessagePublishOperator @Override public Subscriber<? super Message> call(Subscriber<? super PublishResult> child) { final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } @Override public void onCompleted() { child.onCompleted(); } @Override public void onError(Throwable e) { child.onError(e); } }; }
68. MessagePublishOperator final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } };
69. MessagePublishOperator final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } };
70. MessagePublishOperator final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } };
71. MessagePublishOperator final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } };
72. MessagePublishOperator final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } };
73. MessagePublishOperator final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } };
74. MessagePublishOperator @Override public Subscriber<? super Message> call(Subscriber<? super PublishResult> child) { final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } @Override public void onCompleted() { child.onCompleted(); } @Override public void onError(Throwable e) { child.onError(e); } }; }
75. MessagePublishOperator @Override public Subscriber<? super Message> call(Subscriber<? super PublishResult> child) { final ApiClientWrapper apiClient = new ApiClientWrapper(this.context); return new Subscriber<Message>(child) { @Override public void onNext(Message message) { Nearby.Messages.publish(apiClient, message).setResultCallback(status -> { if (status.isSuccess()) { child.onNext(new PublishResult(message)); } else { child.onError(new ApiStatusException(status)); } }); } @Override public void onCompleted() { child.onCompleted(); } @Override public void onError(Throwable e) { child.onError(e); } }; }
76. MessagePublishOperator @Override public void onCompleted() { child.onCompleted(); } @Override public void onError(Throwable e) { child.onError(e); }
77. MessagePublishOperator private void init() { add(new Subscription() { @Override public void unsubscribe() { apiClient.unpublish(); apiClient.disconnect(); } @Override public boolean isUnsubscribed() { return apiClient.isConnected(); } }); }
78. MessagePublishOperator private void init() { add(new Subscription() { @Override public void unsubscribe() { apiClient.unpublish(); apiClient.disconnect(); } @Override public boolean isUnsubscribed() { return apiClient.isConnected(); } }); }
79. Takeaways • Call the child subscriber’s onNext()/onError()/onCompleted appropriately • Make sure any resources and the newly created parent subscriber are released when the child subscriber is unsubscribed • You can use new Subscriber(Subscriber) to make sure the subscription and the back-pressure chains ✓ Note, in that case, all the subscriptions are shared with a child subscriber, which may cause an unexpected behaviour in some cases (See http://akarnokd.blogspot.jp/2015/05/pitfalls- of-operator-implementations.html) • Take care of multiple subscriptions
80. Summary • Subscriber is the core of RxJava • Custom Observable is pretty easy to create • Custom Operator is a bit more hard - Take care of subscriptions and back pressure • Read “RxJava Advanced” - Pitfalls of operator implementations (part 1)
 http://akarnokd.blogspot.jp/2015/05/pitfalls-of-operator- implementations.html
81. Thank you! Hiroshi Kurokawa (ࠇ઒ ༸) @hydrakecat https://github.com/hkurokawa https://speakerdeck.com/hkurokawa hydrakecat.hatenablog.jp