The Reactive Extension library in .NET

1. REACTIVE EXTENSIONS

2. PULL…
• Most programming today is based on a “pull” model
• Ask a data source for an item, wait for the item to be returned,
and then process it
• Our app is active the entire time
• makes the request,
• waits for the result (usually a blocking operation),
• controls the speed at which we process the result

3. …VS PUSH
• The “push” model aims to make our applications less concerned
with the data flow
• Our app asks a data source to notify us if it has data we can use
• The data source is responsible for the notification and sending
of data
• Our app is free to continue on its way, and is simply notified if
there’s new data
• AKA Observer Pattern

4. REACTIVE EXTENSIONS (RX)
• Some neat baked-in interfaces, extension methods, and static
classes for implementing Pull-based (observable pattern)
systems
• Originally announced on Nov 17, 2009
• Included in .NET v4.0

5. IOBSERVABLE<T>
• Interface representing a collection that you can “observe”
• IDisposable Subscribe(IObserver<Type> observer)
only interface method

6. IOBSERVER<T>
• Interface representing something that can observe an
observable
• void OnNext(T data) – called by observable when the
next piece of data is ready
• void OnError(Exception ex) – called by
observable when an error occurs
• void OnCompleted() – called by observable when the
pull operation has completed

7. EXAMPLE!
• Twitter Firehose API Example

8. OBSERVABLE STATIC CLASS
• IObserable/IObserver are all well and good, but we really
could’ve done that without Rx
• Observable/Observer provide static methods to create
Observables/Observers without class definitions
• Provides a whole bunch of options
• Separate install (can be installed from NuGet)

9. OBSERVABLE
• Example Code!

10. SCHEDULER
• By default, Observable will automatically schedule itself on a
certain thread, by default it uses TaskPool
• You can control this by passing in a scheduler
• ImmediateScheduler, CurrentThreadScheduler,
DispatcherScheduler, NewThreadScheduler,
TaskPoolScheduler, ThreadPoolScheduler
• Example Code!

11. RX AND LINQ
• Rx adds a few new LINQ extension methods, as well as uses
the existing ones
• Example Code!

12. OBSERVABLE SUBJECT
• Subject is a proxy class you can use to wrap a non-pull system
and create an observable
• Implements both IObservable<T> and IObserver<T>
• Example Code!

13. IQBSERVABLE
• Combines LINQ’s Queryable and Rx’s Observable functionality
• Queryable – allows you to create a query client side using
LINQ, and pass that query to a data source
(server, database, web service, etc)
• Observable – instead of blocking until the data comes back, will
just let you know when it gets the data