This document discusses dependency injection and inversion of control principles. It explains that high level modules should not depend on low level modules, but both should depend on abstractions. The document advocates asking for dependencies through constructor parameters, properties, and method arguments, while leaving instantiation of dependencies to the caller. This achieves loose coupling and high cohesion. It then discusses how dependency injection containers can help manage dependencies and configure them through sources like XML, attributes, or a registry DSL. Common object lifetimes and patterns like constructor injection are also covered, along with anti-patterns to avoid like the service locator pattern. The document demonstrates examples and use of a dependency injection container.

1. The Dependency |---####>-----
Sorin DAMIAN

2. Agenda
• Dependency injection explained
• SOLID again 
• Loose coupling & high cohesion
• Example
• Containers
• Configuration
• Patterns and anti-patterns
• Unit testing with auto-mocking containers

3. Dependency Injection &
Inversion of Control
• Pt copii de 5 ani
– Nu te bagi direrect in frigider
– Ceri exact ce ai nevoie si altcineva (mami si tati) iti
ofera de mancare
• Pt adulti
– The mafia principle: Don’t call us.. We’ll call U!
• Pt programatori
– O metoda care calculeaza totalul unei facturi nu
trebuie sa extraga fiecare item din baza de date. Este
de ajuns doar sa ceara pretul pentru fiecare item.
Responsabilitatea citirii din db revine caller-ului..

4. SOLID
• S – Single Responsibility Principle
• O – Open/Closed Principle
• L – Liskov Substitution Principle
• I – Interface Segregation Principle
• D – dependency inversion
• High level modules should not depend upon low level
modules. Both should depend upon abstractions.
• Abstractions should not depend upon details. Details
should depend upon abstractions.

5. Tight coupling

6. Loose coupling & high cohesion

7. Example

8. Example

9. Dependency Injection
• Dependency Injection is Inversion of Control
applied to dependency management
– Ask for dependencies using constructor
parameters, properties and method arguments
– Always leave the responsibility of instantiating
dependencies to the caller
• Side effect
– Nobody wants to be the top caller (dependency
injection hell)

10. Dependency Injection
DEMO

11. The DI container
• Solution: the DI container
• Step1 - Unlearning StructureMap
– If you think it’s a factory on steroids, you’re using
it the wrong way!
• Step 2 – wire-up the container
• Step.. DONE 

12. DI/IoC Containers
• Poor man’s dependency injection
• Do it yourself
• StructureMap
• Castle Windsor
• Spring.NET
• LinFu
• Unity
• Autofac
• NInject
• Managed Extensibility Framework (MEF)

13. Configuration
• Sources
– XML
– Attributes
– Registry DSL
• Object lifetime
• Custom instances
• Named instances
• Auto registration and type scanning
– Registries
– Conventions
• Interception

14. Object Lifetime
• PerRequest
• Unique
• Singleton
• HttpContext
• ThreadLocal
• Hybrid
• HttpSession
• HybridHttpSession

15. Configuration
DEMO

16. Anti-patterns
• Control Freak
• Bastard Injection
• Constrained construction
• Service locator

17. Service Locator anti-pattern

18. Patterns
• Constructor injection
• Property injection
• Method injection
• What to inject and what NOT!
– Unstable dependencies
• Doesn’t yet exist
• Machine/environment specific
• Nondeterministic
– No need to inject stable dependencies
• Already exist, behave deterministically, will not be replaced

19. Auto-mocking containers
DEMO

20. Done done