Reactive Extensions

Rx 

• it's a library for .Net
• also available in Java, Javascript, C++, Ruby, Python
• used for building Reactive Applications

Message(Event) Driven

State

Let's try to be polite 

• Don't call other modules functions
• Publish events for communicating
• Give others modules a chance to party

Rx contract

public interface IObservable<out T>
{
    IDisposable Subscribe(IObserver<T> observer);
}

public interface IObserver<in T>
{
    void OnNext(T item);
    void OnCompleted();
    void OnError(Exception error);    
}

OnNext* (OnCompleted | OnError)?

Rx in .Net ecosystem

sync: 

async: 

One

Many

T

Task<T>

IObservable<T>

IEnumerable<T>

Observer pattern

    observable.Subscribe(observer);

Observables

Observables

Observable
    .Return("hello world")
    .Subscribe(message => Console.WriteLine(message));

Observables

Observable.Create<string>(observer => 
    {
        observer.OnNext("test1");
        observer.OnNext("test2");
        observer.OnCompleted();
        return Disposable.Empty;
    }).Subscribe(message => Console.WriteLine(message));

Observables

new int[] { 1, 2, 3 }
    .ToObservable()
    .Subscribe(number => Console.WriteLine(number));

SQL

SELECT name FROM students

SELECT name 
FROM students 
WHERE phoneNumber = "0722334455"

map : 

filter : 

Linq + Rx 

students
    .Select(student => student.Name)
    .Subscribe(name => Console.WriteLine(name))

map:

students
    .Where(student => 
        student.PhoneNumber == "0722334455")
    .Subscribe(student =>
        Console.WriteLine(student.Name))

filter:

• query language over events
• function composition
• call functions by publishing events

New extensions for Rx 

• Merge
• CombineLatest
• Throttle
• Sample
• Timeout
• Delay
• When, And, Then

Common used example

var textChanged = 
    from evt in Observable.FromEvent<EventArgs>(txt, "TextChanged")
    select ((TextBox)evt.Sender).Text;

var input = textChanged
    .Throttle(TimeSpan.FromSeconds(1))
    .DistinctUntilChanged();

var webServiceClient = new HttpClient("http://..");
var searchOnWebService = Observable.FromAsync(webService.SearchAsync);

var results = from term in input
              from webResults in searchOnWebService.TakeUntil(input)
              select webResults 

Schedulers

• Immediate
• CurrentThread
• NewThread
• ThreadPool
• TaskPool
• TestScheduler
• EventLoop

 SubscribeOn, ObserveOn

Observable.Create(observer => {
    printCurrentThread();
    observer.OnNext("hello"); })
.SubscribeOn(Schedulers.Immediate)
.ObserveOn(Schedulers.ThreadPool)
.Subscribe(message => {
    printCurrentThread();
    Console.WriteLine(message); });

Interested ?

• IntroToRx
• Rx-Workshop
• Rx Dev Videos

Success stories

• Reactive UI
• GitHub client for Windows
• Reactive Trader app