The document discusses the advantages of using Reactive Programming (Rx) over traditional event-based programming. Specifically: - Events have awkward syntax for registering callbacks and are difficult to compose. - Rx allows events to be queried over time and provides help for concurrency and multithreading. - Several examples are given of how Rx can be used to handle notifications, buffer log entries over time, and compose file system events that occur within time periods. - The document encourages learning more about Rx through online resources and sample code.

1. Member of the stack since 2009

2. Why Reactive Programming?

3. Events vs Rx: Why Rx is a better model.
• In C#, events have a curious interface. Some find the += and -= operators an
unnatural way to register a callback
• Events are difficult to compose
• Events do not offer the ability to be easily queried over time
• Events are a common cause of accidental memory leaks
• Events do not have a standard pattern for signaling completion
• Events provide almost no help for concurrency or multithreaded applications.
For instance, raising an event on a separate thread requires you to do all of
the plumbing
Events vs Rx

4. Events vs Rx

5. Events vs Rx

6. Events vs Rx

7. Creating an Observable
• Custom using a Subject<T>
• Based on Event (FromEventPattern)
• Several other options:
– ToObservable()
– Observable.Interval(TimeSpan ts)
– Observable.Create(…)
– Many more…

8. Demo - Query over Time
ApplicationLogger.Instance.Write(…)
event EventHandler<EvArgs> LogEntryWritten
Question:
How to get a signal when a certain log entry
occurs more than (n) times in a given time
period?

9. Demo – Composition
FileSystemWatcher
- Deleted event
- Created event
Question:
How would I scan for creates and deletes that
have occurred every (n) minutes?

10. Demo – Threading
SomeEvent(Object sender, SomeEventArgs e)
{
PerformWorkTaking10Seconds (e)
UpdateUi(e)
}
_______________________________________________________________
OnSomeEvent()
{
if(SomeEvent != null)
SomeEvent(this, new SomeEventArgs());
}
With (n) subscribers, how long does it take to complete
OnSomeEvent()?

11. Other Goodies
• React to UI (demo)
• Timeout (demo)
• Lots of Operators
– Where()
– Retry()
– Amb()
– OnErrorResumeNext()
– …

12. Usages in PlanCare 2
• Buffering Web Api Request logentries
• Handling Notifications (Buffer, Transform)
• As Event Substitute in Business Layer

13. And more: PHP, Pearl, Haskeel

14. http://nflx.it/1yR60gV
http://bit.ly/1LOtiH3
http://bit.ly/1E2WpqT
http://bit.ly/1E3dscb

15. What’s Next?
IQbservable<T> - Linq to Services
Subscribe to changes somewhere else

16. Get started …
• http://www.introtorx.com/
• http://rxwiki.wikidot.com/101samples
• http://t.co/gB7SPIcZu3 (Must See!)
… play … and remember:
Often it is not the technique that let's us down, but our implementation of it.