decoupling-ea

Amir Barylko - .NET UG Mar ‘11 MavenThought Inc.

AMIR BARYLKO

DECOUPLINGUSING THE

EVENTAGGREGATOR

.NET USER GROUPMAR 2011

Wednesday, March 30, 2011


WHO AM I?

• Quality Expert

• Architect

• Developer

• Mentor

• Great cook

• The one who’s entertaining you for the next hour!



RESOURCES

• Email: [email protected]

• Twitter : @abarylko

• Blog: http://www.orthocoders.com

• Materials: http://www.orthocoders.com/presentations


mailto:[email protected]


http://www.orthocoders.com/presentations



INTROCouplingCohesion

DependenciesDependency Injection

IoC Containers



COUPLING & COHESION



COUPLING(WIKIPEDIA)

Degree to which each program module relies on each one

of the other modules



COUPLING II

Is usually contrasted with cohesion


http://en.wikipedia.org/wiki/Cohesion_(computer_science)

http://en.wikipedia.org/wiki/Cohesion_(computer_science)


COUPLING III

Invented by Larry Constantine, an original developer of

Structured Design


http://en.wikipedia.org/wiki/Larry_Constantine

http://en.wikipedia.org/wiki/Larry_Constantine


COUPLING IV

Low coupling is often a sign of a well-structured computer system and a

good design


http://en.wikipedia.org/wiki/Computer

http://en.wikipedia.org/wiki/Computer


COUPLING V

When combined with high cohesion, supports high

readability and maintainability



COHESION(WIKIPEDIA)

measure of how strongly-related the functionality expressed by the source code of a

software module is


http://en.wikipedia.org/wiki/Module_(programming)

http://en.wikipedia.org/wiki/Module_(programming)


IS ALL ABOUTDEPENDENCIES



HARDCODEDDEPENDENCIES

public MovieLibrary()

{

this._storage = new LocalStorage();

this._critic = new JaySherman();

this._posterService = new IMDBPosterService();

}

Impossible to test or maintain!



EXTRACT INTERFACES

private JaySherman _critic;

private IMDBPosterService _posterService;

private LocalStorage _storage;

private IMovieCritic _critic;

private IMoviePosterService _posterService;

private IMovieStorage _storage;



DEPENDENCY INJECTION

public MovieLibrary(IMovieStorage storage,

IMovieCritic critic,

IMoviePosterService posterService)

{

this._storage = storage;

this._critic = critic;

this._posterService = posterService;

}

Better for testing... but who is going to initialize them?



INVERSION OF CONTROL



POOR’S MAN DI

public MovieLibrary()

{

this._storage = new LocalStorage();

this._critic = new JaySherman();

this._posterService = new IMDBPosterService();

}

Still testeable...but smells!



USING IOC CONTAINER

Container.Register( Component .For<IMovieCritic>() .ImplementedBy<JaySherman>(), Component .For<IMoviePosterService>() .ImplementedBy<IMDBPosterService>(), Component .For<IMovieStorage>() .ImplementedBy<LocalStorage>());



REFACTORINGWhat’s wrong?

Event AggregatorDemo

Desktop &Web applications



WHAT’S WRONG?



TOO MANY DEPENDENCIES



LET’S THINK

•Why the critic has to know the library (or viceversa)?

•Or the poster service?

• If I need more services, do I add more dependencies to the library?



DECENTRALIZE

• Identify boundaries

• Identify clear responsibilities

•Reduce complexity

•Find notification mechanism



Library

WHAT I’D LIKE

Reviews

Posters

????



EVENT AGGREGATOR



THE PATTERN

Channel events from multiple o b j e c t s i n t o a single object to s i m p l i f y registration for clients



TRAITS

•Based on subject - observer

•Centralize event registration logic

•No need to track multiple objects

•Level of indirection



DEMO



WHAT WE NEED

•Register events

•Raise events

•Subscribe to events



IMPLEMENTATION



WHAT’S NEXT?

•Show movies

•Add notification to show posters

•Add notification to show reviews



QUESTIONS?



RESOURCES

• Email: [email protected]

• Twitter : @abarylko

• Presentation: http://www.orthocoders.com/presentations

• Source Code: https://github.com/amirci/decoupling_mar_11






https://github.com/amirci/democc_2011

https://github.com/amirci/democc_2011


RESOURCES II

•Coupling: http://en.wikipedia.org/wiki/Coupling_(computer_programming)

•Event Aggregator: http://martinfowler.com/eaaDev/EventAggregator.html

MavenThought Commons:https://github.com/amirci/mt_commons

•Bootstrapper:http://bootstrapper.codeplex.com/

•Windsor Container :http://www.castleproject.org/container/


http://en.wikipedia.org/wiki/Coupling_(computer_programming)

http://en.wikipedia.org/wiki/Coupling_(computer_programming)

http://martinfowler.com/eaaDev/EventAggregator.html

http://martinfowler.com/eaaDev/EventAggregator.html

http://bootstrapper.codeplex.com/

http://bootstrapper.codeplex.com/

http://www.castleproject.org/container/

http://www.castleproject.org/container/


TDD TRAINING

• When: May 26 & 27

• More info: http://www.maventhought.com

• Goal: Learn TDD with real hands on examples


http://www.maventhought.com

http://www.maventhought.com


AGILE USER GROUP

• Check it out! : http://www.agilewinnipeg.com

• Apr 5: Agile Planning

• May: Agile Stories

• Jun: Testing?


http://www.agilewinnipeg.com

http://www.agilewinnipeg.com

Technology

decoupling-ea