Functional Reactive Programming

RxJava / RxAndroid

Introduction

• Functional Programming, programming that transform and compose stream of immutable sequences by applying map, filter and reduce.

• Reactive Programming. This model of programming focuses on data flow and change propagation.

Easy analogy for FRP is a spreadsheet application.

You chain the formula, whenever the source cell is changed, the result will change too.

FRP SupportBy http://reactivex.io/

FRP

ReactiveX is a combination of the best ideas from the Observer pattern, the Iterator pattern,

and functional programming

FRP with Java

Observable emits data.

Subscriber consumes those data.

Observable<String> helloObservable = Observable.create( new Observable.OnSubscribe<String>() { @Override public void call(Subscriber<? super String> sub) { sub.onNext("Hello, World!"); sub.onCompleted(); }; });

helloObservable.subscribe( new Action1<String>() { @Override public void call(String s) { System.out.println("Subscriber : " + s); } });

Observable

Observable hook subscriber

Try to add another subscribershelloObservable.subscriber( new Action1<String> { @Override public void call(String s) { System.out.println("Sub2 : " + s); } });

Output:Subscriber : Hello, World!Sub2 : Hello, World!

Transformation

It’s part of functional, allow us to transform observable such as map, filter and others.Ex: (marble notation)

List<String> names = Arrays.asList("Jily", "Iqbal", "Dini", "Reza", "Bagus", "Pp", "Akbar");

Observable<String> helloObservable = Observable.from(names);

helloObservable.subscribe( new Action1<String>() {@Override

public void call( String s ) { String greet = "Sub 1 on " + currentThreadName() + ": Hello " + s + "!"; System.out.println(greet); }

Output:Sub 1 on main: Hello Jily!Sub 1 on main: Hello Iqbal!Sub 1 on main: Hello Dini!Sub 1 on main: Hello Reza!Sub 1 on main: Hello Bagus!Sub 1 on main: Hello Pp!Sub 1 on main: Hello Akbar!

helloObservable.map( new Func1<String, String>() { @Override public String call( String s ) { return s.toUpperCase(); } }).subscribe( new Action1<String>() { @Override public void call( String s ) { String greet = "Sub 1 on " + currentThreadName() + ": Hello " + s + "!"; System.out.println(greet); } });

We want to print uppercased name of the person

Output:Sub 1 on main: Hello JILY!Sub 1 on main: Hello IQBAL!Sub 1 on main: Hello DINI!Sub 1 on main: Hello REZA!Sub 1 on main: Hello BAGUS!Sub 1 on main: Hello PP!Sub 1 on main: Hello AKBAR!

helloObservable.map( s -> s.toUpperCase() ) .subscribe( s -> { String greet = "Sub 1 on " + currentThreadName() + ": Hello" + s + "!"; System.out.println(greet); });

helloObservable.map( s -> s.toUpperCase() ) .map( s -> "Sub 1 on " + currentThreadName() + ": Hello " + s + "!") .subscribe( s -> System.out.println(s));

Concise & Concise (by lambda expression)

More readable

Real Case (android register activity)

References

• https://github.com/faren/RxAndroidProject• https://www.ykode.com/2015/02/20/android-

frp-rxjava-retrolambda.html

• http://blog.danlew.net/2014/09/15/grokking-rxjava-part-1/