Reactive Extensions (Rx) Explained

Presenter:Kevin GrossnicklausAugust 5th, 2011

Agenda

• Introductions• Talk• Additional Resources• Conclusion

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

EXPECTATIONS

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

INTRODUCTION TO RX

IEnumerable/IEnumeratorinterface IEnumerable<T>{

IEnumerator<T> GetEnumerator();}

interface IEnumerator<T> : IDisposable{

bool MoveNext();T Current { get; }void Reset();

}

Iterating Collectionsvar 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

IObservable/IObserverinterface IObservable<out T>{

IDisposable Subscribe(IObserver<T> observer);}

interface IObserver<in T>{

void OnNext(T value);void OnError(Exception ex);void OnCompleted();

}

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();

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

OBSERVABLE EXTENSIONS

Subjectsusing 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();

Subscribingpublic 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); }

Creation of Observables//simply call OnCompletevar empty = Observable.Empty<string>();

//Call OnNext(“Value”) and then call OnCompletevar obReturn = Observable.Return("Value");

//Raise no eventsvar never = Observable.Never<string>();      

//Call OnException with the specified expectionvar throws = Observable.Throw<string>(new Exception());

//Specify a delegate to be called when anyone subscribesvar createSample = Observable.Create<string>( observable => {

observable.OnNext("a"); observable.OnNext("b"); observable.OnCompleted(); return () => Console.WriteLine("Observer has unsubscribed");

});

Creation of Observables (Cont…)//Create a range of numbersvar range = Observable.Range(10, 15);

//publish a count from 0 every specified time periodvar interval = Observable.Interval(TimeSpan.FromMilliseconds(250));

//Never call “Next” but call “Complete” when the long running operation is donevar longOperation = 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 IObservablevar converted = MyCollection.ToObservable();

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…

RX AND .NET EVENTS

The “Old Way”

txtSample.TextChanged += new TextChangedEventHandler(txtSample_TextChanged);             //txtSample.TextChanged  -= new TextChangedEventHandler(txtSample_TextChanged);                  private string _lastValue = string.Empty;         

void txtSample_TextChanged(object sender, TextChangedEventArgs e)         {             

var _currentValue = ((TextBox)sender).Text;             

if (_currentValue.Length > 5 && _currentValue != _lastValue)              {                  

_lastValue = _currentValue;                 lstData.Items.Add(_currentValue);             

}         }

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));

ADDITIONAL TOPICS

Additional Topics

• Threading– Scheduler

• Async Pattern• Attaching/Detaching

• When should I use Rx?

FINAL THOUGHTS

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

Next Steps…

kvgros@architectnow.netTwitter: @kvgros