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

ObserverObserver (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 ClicksSimulate a stream of clicks:

Ex. Double ClicksAccumulate clicks until 250 ms has passed between clicks:

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

GitHub Example● Interact with GitHub’s API using Retrofit and RxJava

○ https://github.com/arriolac/GithubRxJava

Questions??

Thank You!

Twitter: @arriolachris