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Intro to Dependency Injection & Inversion of Control

Intro to Dependency Injection & Inversion of Control. Presenter - Donn Felker. About Me – Donn Felker. Senior Consultant for Microsoft Gold Certified Partner- Statêra. 8 years of experience in developing and architecting enterprise solutions. Certifications:

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Intro to Dependency Injection & Inversion of Control

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  1. Intro to Dependency Injection & Inversion of Control Presenter - Donn Felker

  2. About Me – DonnFelker • Senior Consultant for Microsoft Gold Certified Partner- Statêra. • 8 years of experience in developing and architecting enterprise solutions. • Certifications: • Microsoft Certified Technology Specialist • Certified SCRUM Master • ITIL Foundation Certified • Bachelors of Science in Software Engineering • Member of FooTheory Community (www.footheory.com) • Blog: http://blog.donnfelker.com • Email: donn@donnfelker.com

  3. What I intend to do… • Present Dependency Injection and Inversion of Control in an understandable fashion • Present each topic at a detailed but comprehendible level • Give you the resources used in this talk so you can reference them in the future.

  4. What I DO NOT intend to do… • Confuse you. • Pretend to be an authority in patterns, because, well … I’m not. • Get all “Fowler” on you. • Have theoretical conversations about practicality of the example apps I’m using for demonstration purposes.

  5. Agenda • What is a Dependency? • Dependency Injection Pros/Cons • Simple Application Architecture • Example Application High Level Architecture • Demonstration 1 • Identifying and Breaking dependencies • What is Inversion of Control • Demonstration 2 • Custom Dependency Container • Introducing Microsoft Unity Container • Questions

  6. What is a “Dependency”? • Some common dependencies include: • Application Layers • Data Access Layer & Databases • Business Layer • External services & Components • Web Services • Third Party Components • .NET Framework Components • File Objects (File.Delete(…), Directory.Exists(…)) • Web Objects (HttpContext, Session, Request, etc)

  7. Dependencies at a Very High Level BROKEN BUILD! CI Server

  8. Get a Resource Involved…

  9. Example of a Dependency

  10. What problems do dependencies create? • Code is tightly coupled • Difficult to isolate when testing • Difficult to maintain • If I change ComponentX how do I know what else it will affect? Did I break anything? • If tests are in place they can be your safety net

  11. What is Dependency Injection? • The ability to supply (inject) an external dependency into a software component. • Types of Dependency Injection: • Constructor (Most popular) • Setter • Method

  12. Constructor Injection Injecting a ICustomerRepository and a ICustomerDTOMapper through the constructor. Note: This is the most popular type of injection.

  13. Setter Injection Injecting a ICustomerRepository through the setter.

  14. Method Injection Injecting a ICustomerRepository as well as an integer dependency.

  15. Dependency Injection Pros & Cons • Pros • Loosely Coupled • Increases Testability (A LOT!) • Separates components cleanly • Allows for use of Inversion of Control Container • Cons • Increases code complexity • Some Jr. Developers find it difficult to understand at First • Can Complicate Debugging at First • Complicates following Code Flow

  16. Overview of Example Application

  17. Demonstration Lets See Some Code…

  18. What is Inversion of Control • Sometimes referred to as 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 implementations (object instances) are deferred to a higher level of abstraction of control. • Examples: • Parent class(es) • A Container • Referred to as the “Hollywood Principle” • “Don’t call us, we will call you.”

  19. IoC Demonstration The best example is to see it in code.

  20. Questions?

  21. Resources • Containers • Windsor: http://shrinkster.com/ym6 • Unity: http://shrinkster.com/ym5 • Structure Map: http://shrinkster.com/ym7 • Spring.NET: http://shrinkster.com/ym8 • Unity Screencast (PnP Guidance) • http://shrinkster.com/yma • Good Book to help break dependencies: • Working Effectively with Legacy Code (Michael Feathers) • http://shrinkster.com/ym9 • Contact Me • donn@donnfelker.com • http://blog.donnfelker.com • All resources from this talk will be posted within 24 hours on this blog.

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