Dependency injection is a technique for achieving loose coupling between software components by supplying an external dependency to a component at runtime. This allows for increased testability and flexibility in configuring applications. The document compares two popular dependency injection frameworks for .NET applications - Spring.NET and Microsoft Unity - describing their basic architectures, types of dependency injection they support, advantages like loose coupling and disadvantages like increased complexity.

1. Dependency Injection & Inversion of Control Unity Application Block vs. Spring.NET Dennis Loktionov [email_address] February 2009

2. Agenda What is a Dependency? Dependency Injection Pattern Injection Types Dependency Injection Pros & Cons Spring.NET vs. MS Unity Application Block References Questions

3. What is a Dependency? Common Dependencies Application Layers -- Data Access Layer -- Business Layer -- Presentation Layer External Services -- Web Services -- WCF Services External Components -- Frameworks & Libraries -- 3 rd Party Components

4. Application Layers Dependencies

5. Why dependencies are evil? Problems that dependencies create Tight coupling of software components Software becomes hard to maintain Difficult to isolate when testing

6. Dependency Injection Pattern WHAT Dependency Injection (DI) in computer programming refers to the process of supplying an external dependency to a software component or service. WHY Ability to specify component dependencies at run time Simplified management of cross-cutting concerns Increased testability of individual components Need for pluggable architecture

7. Dependency Injection Types Types of Dependency Injection Constructor Injection Property (Setter) Injection Method Call Injection

8. Dependency Injection Types Constructor Injection

9. Dependency Injection Types Property (Setter) Injection

10. Dependency Injection Types Method Call Injection

11. Dependency Injection Pros & Cons Pros Loosely Coupled & Highly Cohesive Increased Testability & Maintainability Flexibility of run time configuration Inversion of Control containers do the wiring for you Cons Increased code complexity Can complicate debugging during the learning curve Code flow becomes not trivial

12. Inversion of Control Dependency Inversion Principle (DIP) The principle states that high level or low level modules should not depend upon each other, instead they should depend upon abstractions. Specific implementation (object instances) are deferred to a higher level of abstraction control. Parent Classes Container

13. Frameworks Frameworks Spring.NET MS Unity Application Block Castle Windsor StructureMap Ninject PicoContainer.NET … and many more

14. Spring.NET Spring.NET Architecture

15. Spring.NET Inversion of Control Container in Action

16. Spring.NET: code samples Movie Lister example

17. MS Unity Application Block Unity Application Block Architecture

18. Unity: code samples Movie Lister example Quick start web example

19. Dependency Injection Pitfalls Circular References Objects generated though constructor injection that reference each other in their constructor parameters Objects generated though constructor injection that pass a reference of their type in constructor Objects generated though method call injection that reference each other Objects generated though property injection that reference each other Partial Trust Environment Limitations

20. References Useful links: http://martinfowler.com/articles/injection.html http://www.springframework.net/ http://www.codeplex.com/unity

21. THANKS

22. Questions ? Dennis Loktionov [email_address] 604-628-5100 ext .356