Intro to RxJava on Android Chris Arriola Functional Reactive Programming

● Makes dealing with concurrency easy ● Makes code a lot more concise and readable ● Encourages defensive programming and makes error handling easy ● Increases the level of abstraction Why consider RxJava?

Nested Network Call w/o RxJava

Nested Network Call w/ RxJava

What is RxJava? ● Java implementation of .NET’s Reactive Extensions ○ Specification for Functional Reactive Programming (FRP) ● Programming with asynchronous data streams ○ Not a new concept. Think: click events/handlers, event bus, etc. ○ Reactive part ● Can combine, create, filter, map, or transform any stream ○ Functional part

Core RxJava Constructs ● Observable ● Observer ● Operator

● Emits items in a sequence ○ Like an Iterator, it produces all items in a sequence ● Each emitted item will be propagated to each Observer Observable

Observer ● Observer (aka the “subscriber”) subscribes to Observable ● Observers are notified of a new item through #onNext(...) ● Observers are notified when there sequence completes/fails through #onCompleted()/#onError()

Creating an Observable ● Create an Observable using #create(...)

Creating an Observable ● Create an Observable from item/s using #just(...) ● Create an Observable from an Iterable using #from(...) ● Create an Observable that emits items given an interval using #interval(...)

Creating an Observable (cont’d) ● Defer creation of Observable until subscription

Subscribing to an Observable ● Observer has #onNext(...), #onCompleted(...), and #onError(...)

Unsubscribing to an Observable ● Observable#subscribe(...) returns a Subscription object from which the caller can invoke Subscription#unsubscribe()

Operator ● Most powerful part about Observables is that you can transform them and perform functional style programming—map(), debounce(), filter(), etc. ● Transform Observable instances through Operators

Operator

Transforming an Observable ● Transform values emitted by Observable using the #map(...) operator

Filtering an Observable ● Filter values emitted by Observable using #filter(...) operator

Scheduling an Observable ● Specify a Scheduler where the Observable should operate using #subscribeOn(...), specify a Scheduler where the Observable should notify its observers using #observeOn(...)

Error Handling ● Re-subscribe/retry when the Observable emits an error

Ex. Double Clicks ● Stream of clicks ● Accumulate clicks in a list ● Get length of list ● Filter

Ex. Double Clicks Simulate a stream of clicks:

Ex. Double Clicks Accumulate clicks until 250 ms has passed between clicks:

Ex. Double Clicks Map the length of each list & filter for sizes >= 2:

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GitHub Example ● Interact with GitHub’s API using Retrofit and RxJava ○ https://github.com/arriolac/GithubRxJava

Questions??

Thank You! Twitter: @arriolachris