Reactive Extensions (Rx) Explained

1. Reactive Extensions (Rx) Explained Presenter: Kevin Grossnicklaus August 5th, 2011

3. Agenda • Introductions • Talk • Additional Resources • Conclusion

4. Introductions • Kevin Grossnicklaus • ArchitectNow-www.architectnow.net (2009-Present) • President • Washington University - CAIT Program (2003-2010) • Instructor • SSE - www.SSEinc.com (1999-2009) • Chief Architect • Software Development Practice Leader • Email: kvgros@architectnow.net • Twitter: @kvgros • Blog: blog.architectnow.net

5. Expectations

6. Expectations • Experience with .NET development • Samples will be in C# 4.0 • VS 2010 will be used • Basic familiarity with LINQ and some Async programming • Lambda Expressions will be used

7. Introduction to Rx

8. IEnumerable/IEnumerator interface IEnumerable<T> { IEnumerator<T> GetEnumerator(); } interface IEnumerator<T> : IDisposable { boolMoveNext(); T Current { get; } void Reset(); }

9. Iterating Collections var items = new string[] { “Hello”, “World” }; foreach (var x in items) { //interact with each piece of data } //we can now assume we are done //we must also handle exceptions

10. IObservable/IObserver interface IObservable<out T> { IDisposable Subscribe(IObserver<T> observer); } interface IObserver<in T> { void OnNext(T value); void OnError(Exception ex); void OnCompleted(); }

11. IObservable/IObserver var _data = new string[] { "Hello", "World" };   var _observable = _data.ToObservable(); var _observer = _observable.Subscribe(x => Console.WriteLine(x)); var _observer2 = _observable.Subscribe(                 x => Console.WriteLine(x),                 () => Console.WriteLine("Completed")); var _observer3 = _observable.Subscribe(                  x => Console.WriteLine(x),                  ex => Console.WriteLine("Exception: " + ex.Message), () => Console.WriteLine("Completed")); _observer2.Dispose();

12. Getting Rx Installed • NuGet • Easiest and quickest • Rx Home Page: • http://msdn.microsoft.com/en-us/data/gg577609 • Simply add a reference to: • System.Reactive.DLL • Available for: • Full Framework (WPF, WinForms, server side ASP.NET, MVC, etc) • Silverlight 3 and 4 • JavaScript • Windows 7 Phone • Xbox/XNA

13. Observable Extensions

14. Subjects using System.Reactive.Subjects; var _subject = new Subject<string>();      var _observer = _subject.Subscribe(x => Console.WriteLine(x)); _subject.OnNext("Rx");              _subject.OnNext("will");             _subject.OnNext("save");              _subject.OnNext("me");              _subject.OnNext("some");             _subject.OnNext("headaches");              _subject.OnCompleted(); _observer.Dispose();

15. Subscribing public static class ObservableExtensions { public static IDisposable Subscribe<TSource>(this IObservable<TSource> source); public static IDisposable Subscribe<TSource>(this IObservable<TSource> source, Action<TSource> onNext); public static IDisposable Subscribe<TSource>(this IObservable<TSource> source, Action<TSource> onNext, Action<Exception> onError); public static IDisposable Subscribe<TSource>(this IObservable<TSource> source, Action<TSource> onNext, Action onCompleted); public static IDisposable Subscribe<TSource>(this IObservable<TSource> source, Action<TSource> onNext, Action<Exception> onError, Action onCompleted); }

16. Creation of Observables //simply call OnComplete varempty = Observable.Empty<string>(); //Call OnNext(“Value”) and then call OnComplete varobReturn = Observable.Return("Value"); //Raise no events varnever = Observable.Never<string>();       //Call OnException with the specified expection var throws = Observable.Throw<string>(new Exception()); //Specify a delegate to be called when anyone subscribes varcreateSample = Observable.Create<string>( observable => { observable.OnNext("a"); observable.OnNext("b"); observable.OnCompleted(); return () => Console.WriteLine("Observer has unsubscribed"); });

17. Creation of Observables (Cont…) //Create a range of numbers var range = Observable.Range(10, 15); //publish a count from 0 every specified time period var interval = Observable.Interval(TimeSpan.FromMilliseconds(250)); //Never call “Next” but call “Complete” when the long running operation is done varlongOperation = Observable.Start( x => ..do something that takes awhile.. ); //Generate a collection much like for (i=5, i<15, i+3) return i.ToString(); var generated = Observable.Generate(5, i => i < 15, i => i.ToString(), i => i + 3); //simply convert an existing collection or array (IEnumerable) to IObservable var converted = MyCollection.ToObservable();

18. Rx LINQ Operators • Where • Select • First • FirstOrDefault • Last • LastOrDefault • Single • Count • Min • Max • Sum • Where • GroupBy • Take • TakeUntil • Skip • DistinctUntilChanged • Buffer • Throttle • Sample • Delay • Until • TimeOut • ..etc…etc…etc…

19. RX and .NET EVENTS

20. The “Old Way” txtSample.TextChanged += new TextChangedEventHandler(txtSample_TextChanged);              //txtSample.TextChanged -= new TextChangedEventHandler(txtSample_TextChanged);         private string _lastValue = string.Empty;          voidtxtSample_TextChanged(object sender, TextChangedEventArgs e)          { var _currentValue = ((TextBox)sender).Text;              if (_currentValue.Length > 5 && _currentValue != _lastValue)             { _lastValue = _currentValue;                  lstData.Items.Add(_currentValue);              } }

21. The “New Way” var _textChanged = Observable .FromEventPattern<EventArgs>(txtSample, "TextChanged") .Select(x => ((TextBox)x.Sender).Text);              var _longText = _textChanged .Where(x => x.Length > 5) .DistinctUntilChanged() .Throttle(TimeSpan.FromSeconds(.5));   _longText .ObserveOnDispatcher() .Subscribe(x => lstData.Items.Add(x));

22. Additional Topics

23. Additional Topics • Threading • Scheduler • Async Pattern • Attaching/Detaching • When should I use Rx?

24. Final Thoughts

25. Additional Resources • Rx Homepage • http://msdn.microsoft.com/en-us/devlabs/gg577609 • Rx Beginners Guide (Tutorials, Videos, etc) • http://msdn.microsoft.com/en-us/devlabs/gg577611 • Great Keynote Overview • http://channel9.msdn.com/posts/DC2010T0100-Keynote-Rx-curing-your-asynchronous-programming-blues • Team Blog • http://blogs.msdn.com/b/rxteam/ • Community Rx Wiki • http://rxwiki.wikidot.com/ • Channel 9 Videos • http://channel9.msdn.com/tags/Rx/ • RxSandbox • http://mnajder.blogspot.com/2010/03/rxsandbox-v1.html • Great Blog Series by Lee Campbell • http://leecampbell.blogspot.com/2010/08/reactive-extensions-for-net.html

26. Next Steps… kvgros@architectnow.net Twitter: @kvgros