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Introduction to Reactive Extensions

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An introduction to the Reactive Extensions (Rx) framework by Microsoft. Rx provides a simpler event model for handling streams of events in asynchronous and event based programs

An introduction to the Reactive Extensions (Rx) framework by Microsoft. Rx provides a simpler event model for handling streams of events in asynchronous and event based programs

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Introduction to Reactive Extensions

  1. 1. 1 Introduction to Reactive Extensions Peter Goodman An Introduction to Reactive Extensions
  2. 2. 2 Introduction to Reactive Extensions What are Reactive Extensions?
  3. 3. 3 Introduction to Reactive Extensions What are Reactive Extensions?
  4. 4. 4 Introduction to Reactive Extensions What are Reactive Extensions?
  5. 5. 5 Introduction to Reactive Extensions What are Reactive Extensions?
  6. 6. 6 Introduction to Reactive Extensions Events in .Net form1.MouseMove += (sender, args) => { if (args.Location.X == args.Location.Y) // I’d like to raise another event }; form1.MouseMove -= /* what goes here? */
  7. 7. 7 Introduction to Reactive Extensions Collections are Enumerables interface IEnumerable<out T> { IEnumerator<T> GetEnumerator(); } interface IEnumerator<out T> : IDisposable { bool MoveNext(); T Current { get; } void Reset(); }
  8. 8. 8 Introduction to Reactive Extensions What if events were collections?  Collection Move Next Move Next Move Next Move Next Move Next Move Next  Event Stream TIME OnNext OnNext OnNext OnNext OnNext OnNext
  9. 9. 9 Introduction to Reactive Extensions Observables interface IObservable<out T> { IDisposable Subscribe(IObserver<T> observer); } interface IObserver<in T> { void OnNext(T value); void OnError(Exception ex); void OnCompleted(); }
  10. 10. 10 Introduction to Reactive Extensions Summary Push vs Pull Application Interactive MoveNext Reactive Got next? OnNext Have next! IEnumerable<T> IObservable<T> IEnumerator<T> IObserver<T> Environment
  11. 11. 11 Introduction to Reactive Extensions Creating 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
  12. 12. 12 Introduction to Reactive Extensions Creating Observables - Range OnNext(0) OnNext(1) OnNext(2) .Range(0, 3) yield 0 yield 1 yield 2 .Range(0, 3)
  13. 13. 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 Synchronous o.Subscribe(x => { foreach (var x in e) { Console.WriteLine(x); Console.WriteLine(x); }); }
  14. 14. 14 Introduction to Reactive Extensions Subscribing IObservable<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"); } );
  15. 15. 15 Introduction to Reactive Extensions DEMO Generating events and subscribing to them
  16. 16. 16 Introduction to Reactive Extensions Observable 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 Select var from in Observable MouseEventArgs select .Location // Filtering for the first bisector using Where var from in where select
  17. 17. 17 Introduction to Reactive Extensions DEMO Querying, Composition and introducing Concurrency
  18. 18. 18 Introduction to Reactive Extensions Introducing 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)
  19. 19. 19 Introduction to Reactive Extensions Introducing 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
  20. 20. 20 Introduction to Reactive Extensions Concurrency and Synchronization • var Observable.Return Scheduler.ThreadPool " " • .ObserveOnDispatcher() " "
  21. 21. 21 Introduction to Reactive Extensions DEMO Synchronization
  22. 22. 22 Introduction to Reactive Extensions Rx 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
  23. 23. 23 Introduction to Reactive Extensions DEMO Rx for JavaScript
  24. 24. 24 Introduction to Reactive Extensions Reactive Extensions Questions?
  25. 25. 25 Introduction to Reactive Extensions Resources  MSDN  Bart de Smet / Rx (Channel 9)  Reactive UI  Pushqa / SignalR
  26. 26. 26 Introduction to Reactive Extensions Contact  pete@petegoo.com  http://blog.petegoo.com  Twitter: @petegoo

Editor's Notes

  • Who am I?Rx was developed by the Cloud Programmability Team
  • - Composing gives us a hint at the Linq style fluent API
  • Async and event-based programs. Recent initiatives including TPL, async/await etc
  • You can’t pass an event aroundThe syntax is very unique and requires cleaning up of subscriptionsYou can’t compose events into new events easily.
  • Lets look at an ordinary collection in .NetNotice in IEnumerable we FETCH an EnumeratorMoveNext pulls the next value from the collection synchronously into Current. It could have just as easily returned the current value from MoveNextReset is an oddity of historyWe are done when there are no more items and MoveNext returns true
  • Observables turn the whole thing on it’s headNotice in Iobservable we get FED an ObserverOnNext pushed the next value from onto the collection asynchronously. OnError occurs when an exception has happened.OnCompleted happens when there are no more items
  • Observable.Return(42).Subscribe(Console.WriteLine)Observable.Range(0,20). Subscribe(Console.WriteLine)Observable.Generate( 0,i =&gt; i &lt; 20, i =&gt; i+1, i =&gt; i*i) .Subscribe(Console.WriteLine);Observable.Generate( 0,i =&gt; i &lt; 20, i =&gt; i+1, i =&gt; i*i) .Subscribe(Console.WriteLine);var sub = Observable.Interval(TimeSpan.FromSeconds(1)).Subscribe(Console.WriteLine);var sub = Observable.Interval(TimeSpan.FromSeconds(1)).Take(3).Subscribe(Console.WriteLine);Observable.Interval(TimeSpan.FromSeconds(1)).Take(3).Subscribe(Console.WriteLine, e =&gt; { }, () =&gt; Console.WriteLine(&quot;Complete&quot;));
  • Observable.Range(0, 20).Where(x =&gt; x % 2 ==0).Subscribe(Console.WriteLine)Observable.Range(0, 20).Where(x =&gt; x % 2 ==0).Select(x =&gt; x*x).Subscribe(Console.WriteLine)Observable.Range(0, 20).Zip(Observable.Interval(TimeSpan.FromSeconds(1)), (x,y) =&gt; x).Where(x =&gt; x % 2 == 0).Subscribe(Console.WriteLine);
  • From Blank AutoCompleteShow project structureCreate search based off property changed event handler** How would we do this with Rx?**Create propertyChanges, searchTextChanges and subscribeRun** What about blocking the UI thread?**Add doSearch, select many and subscriptionRun ** What about the exception?**ObserveOnDispatcherRun** What about too many searches?**Throttle** What about adding support for pressing enter?**TextBoxEnterCommand (Merge)** What about the duplicates?**DistinctUntilChanged** What about results coming back out of sequence?** (Temporarily remove throttle to show)TakeUntil
  • Show codeRunIncrease throttle time
  • ×