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1 Introduction to Reactive ExtensionsPeter GoodmanAn Introduction to ReactiveExtensions

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2 Introduction to Reactive ExtensionsWhat are Reactive Extensions?

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3 Introduction to Reactive ExtensionsWhat are Reactive Extensions?

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4 Introduction to Reactive ExtensionsWhat are Reactive Extensions?

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5 Introduction to Reactive ExtensionsWhat are Reactive Extensions?

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6 Introduction to Reactive ExtensionsEvents in .Netform1.MouseMove += (sender, args) => { if (args.Location.X == args.Location.Y) // I’d like to raise another event};form1.MouseMove -= /* what goes here? */

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7 Introduction to Reactive ExtensionsCollections are Enumerablesinterface IEnumerable<out T>{ IEnumerator<T> GetEnumerator();}interface IEnumerator<out T> : IDisposable{ bool MoveNext(); T Current { get; } void Reset();}

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8 Introduction to Reactive ExtensionsWhat if events were collections?  CollectionMove Next Move Next Move Next Move Next Move Next Move Next  Event Stream TIMEOnNext OnNext OnNext OnNext OnNext OnNext

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9 Introduction to Reactive ExtensionsObservablesinterface IObservable<out T>{ IDisposable Subscribe(IObserver<T> observer);}interface IObserver<in T>{ void OnNext(T value); void OnError(Exception ex); void OnCompleted();}

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10 Introduction to Reactive Extensions Summary Push vs Pull ApplicationInteractive MoveNext Reactive Got next? OnNext Have next! IEnumerable<T> IObservable<T> IEnumerator<T> IObserver<T> Environment

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11 Introduction to Reactive ExtensionsCreating Observables - Primitive OnCompleted .Empty<int>() new int[0] OnNext .Return(42) new[] { 42 } OnError .Throw<int>(ex) Throwing iterator .Never<int>() Iterator that got stuck Notion of time

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12 Introduction to Reactive ExtensionsCreating Observables - Range OnNext(0) OnNext(1) OnNext(2) .Range(0, 3) yield 0 yield 1 yield 2 .Range(0, 3)

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13 Introduction to Reactive Extensions Generating values and Subscribing A variant with time notion Hypothetical anonymous exists (GenerateWithTime) iterator syntax in C#o = Observable.Generate( e = new IEnumerable<int> { 0, for (int i = 0; i => i < 10, i < 10; i => i + 1, i++) i => i * i yield return i * i;); }; Asynchronous Synchronouso.Subscribe(x => { foreach (var x in e) { Console.WriteLine(x); Console.WriteLine(x);}); }

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14 Introduction to Reactive ExtensionsSubscribingIObservable<int> o = Observable.Create<int>(observer => { // Assume we introduce concurrency (see later)… observer.OnNext(42); observer.OnCompleted();});IDisposable subscription = o.Subscribe( onNext: x => { Console.WriteLine("Next: " + x); }, onError: ex => { Console.WriteLine("Oops: " + ex); }, onCompleted: () => { Console.WriteLine("Done"); });

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15 Introduction to Reactive ExtensionsDEMOGenerating events and subscribing to them

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16 Introduction to Reactive ExtensionsObservable Querying Observables are sources of data  Data is sent to you (push based)  Extra (optional) notion of time. Hence we can query over them// Producing an IObservable<Point> using Selectvar from in Observable MouseEventArgs select .Location// Filtering for the first bisector using Wherevar from in where select

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17 Introduction to Reactive ExtensionsDEMOQuerying, Composition and introducing Concurrency

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18 Introduction to Reactive ExtensionsIntroducing Asynchrony An Asynchronous operation can be thought of as an Observable that returns a single value and completes. FromAsync  Takes an APM method pair (BeginExecute, EndExecute) and creates an Observable ToAsync  Takes a method and creates an Observable (Like TPL)

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19 Introduction to Reactive ExtensionsIntroducing Concurrency Many operators in Rx introduce Concurrency  Throttle  Interval  Delay  BufferWithTime Generally they provide an overload to supply a Scheduler  ImmediateScheduler – Static Immediate  CurrentThreadScheduler – Placed on a queue for the current thread  NewThreadScheduler – Spawn a new Thread  DispatcherScheduler - Silverlight  TaskPoolScheduler - TPL  ThreadPoolScheduler

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20 Introduction to Reactive Extensions Concurrency and Synchronization• var Observable.Return Scheduler.ThreadPool " "• .ObserveOnDispatcher() " "

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21 Introduction to Reactive ExtensionsDEMOSynchronization

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22 Introduction to Reactive ExtensionsRx for JavaScript (RxJS) Parity with Rx for .NET  Set of operators  Taming asynchronous JS JavaScript-specific bindings  jQuery  ExtJS  Dojo  Prototype  YUI3  MooTools  Bing APIs

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23 Introduction to Reactive ExtensionsDEMORx for JavaScript

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24 Introduction to Reactive ExtensionsReactive ExtensionsQuestions?

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25 Introduction to Reactive ExtensionsResources MSDN Bart de Smet / Rx (Channel 9) Reactive UI Pushqa / SignalR

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26 Introduction to Reactive ExtensionsContact pete@petegoo.com http://blog.petegoo.com Twitter: @petegoo