Clean Code II - Dependency Injection
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The document presents a talk by Theo Jungeblut on dependency injection, emphasizing its role in clean code and maintainability. It covers the principles of dependency injection, its benefits such as code extensibility and maintainability, and various methods of implementation. The talk also references key concepts and patterns, along with resources for further reading on the topic.
![Inversion of Control –
Setter (Property) Injection
// UNITY Example
public class ContactManager : IContactManager
{
[Dependency]
public IContactPersistence ContactPersistence
{
get { return this.contactPersistence; }
set { this.contactPersistence = value; }
}
}
http://www.martinfowler.com/articles/injection.html](https://image.slidesharecdn.com/2014-10-11cleancodepartii-dependencyinjection-141014022241-conversion-gate01/85/Clean-Code-II-Dependency-Injection-35-320.jpg)
Clean Code II - Dependency Injection
- 1. Evergreen Valley College, Oct. 3rd, 2015 Clean Code II Dependency Injection
- 2. Theo Jungeblut • Director Customer Success at AppDynamics in San Francisco • Coder & software craftsman by night, first time dad and house builder • Architects decoupled solutions & crafts maintainable code to last • Worked in healthcare and factory automation, building mission critical applications, framework & platforms • Degree in Software Engineering and Network Communications • Enjoys cycling, running and eating [email protected] www.designitright.net
- 3. We are hiring! http://www.appdynamics.com/ careers
- 4. Your feedback is important! http://speakerrate.com/speakers/18667-theo-jungeblut
- 5. Where to get the Slides http://www.slideshare.net/theojungeblut
- 6. Overview • What is the issue? • What is Dependency Injection? • What are Dependencies? • What is the IoC-Container doing for you? • What, how, why? • Q & A
- 7. UI Layer Service Layer Business Layer Data Layer Web UI Service ProcessorProcessor Service RepositoryRepository Mobile UI Processor A cleanly layered Architecture
- 8. What is the problem?
- 10. What is Clean Code?
- 11. Clean Code is maintainable Source code must be: • readable & well structured • extensible • testable
- 12. Code Maintainability * Principles Patterns Containers Why? How? What? Extensibility Clean Code Tool reuse * from: Mark Seemann’s “Dependency Injection in .NET” presentation Bay.NET 05/2011
- 14. Without Dependency Injection public class ExampleClass { private Logger logger; public ExampleClass() { this.logger = new Logger(); this.logger.Log(“Constructor call”); } }
- 15. public class ExampleClass { private Logger logger; public ExampleClass() { this.logger = new Logger(); this.logger.Log(“Constructor call”); } } Without Dependency Injection
- 16. Inversion of Control – Constructor Injection http://www.martinfowler.com/articles/injection.html public class ExampleClass { private ILogger logger; public ExampleClass(ILogger logger) { this.logger = logger; if (logger == null) { throw new ArgumentNullException(“logger”); } this.logger.Log(“Constructor call”); } }
- 18. Benefits of Dependency Injection Benefit Description Late binding Services can be swapped with other services. Extensibility Code can be extended and reused in ways not explicitly planned for. Parallel development Code can be developed in parallel. Maintainability Classes with clearly defined responsibilities are easier to maintain. TESTABILITY Classes can be unit tested. * from Mark Seemann’s “Dependency Injection in .NET”, page 16
- 20. Stable Dependency “A DEPENDENCY that can be referenced without any detrimental effects. The opposite of a VOLATILE DEPENDENCY. “ * From Glossary: Mark Seemann’s “Dependency Injection in .NET”
- 21. Volatile Dependency “A DEPENDENCY that involves side effects that may be undesirable at times. This may include modules that don’t yet exist, or that have adverse requirements on its runtime environment. These are the DEPENDENCIES that are addressed by DI.“ * From Glossary: Mark Seemann’s “Dependency Injection in .NET”
- 22. Lifetime a Job for the Container
- 23. public class ExampleClass { private Logger logger; public ExampleClass() { this.logger = new Logger(); this.logger.Log(“Constructor call”); } } Without Dependency Injection
- 24. “Register, Resolve, Release” “Three Calls Pattern by Krzysztof Koźmic: http://kozmic.pl/ 1. Register 2. Resolve Build up Your code Execut e Release Clean up
- 25. What the IoC-Container will do for you 1. Register 2. Resolve Build up Release Clean up
- 26. Separation of Concern (SoC) probably by Edsger W. Dijkstra in 1974 You codeExecute • Focus on purpose of your code • Know only the contracts of the dependencies • No need to know implementations • No need to handle lifetime of the dependencies
- 27. The 3 Dimensions of DI 1.Object Composition 2.Object Lifetime 3.Interception
- 28. Register - Composition Root • XML based Configuration • Code based Configuration • Convention based (Discovery)
- 29. Resolve Resolve a single object request for example by Constructor Injection by resolving the needed object graph for this object.
- 30. Release Release objects from Container when not needed anymore.
- 31. Anti Patterns
- 33. // UNITY Example internal static class Program { private static UnityContainer unityContainer; private static SingleContactManagerForm singleContactManagerForm; private static void InitializeMainForm() { singleContactManagerForm = unityContainer.Resolve<SingleContactManagerForm>(); } } Inversion of Control – Service Locator http://www.martinfowler.com/articles/injection.html
- 34. // UNITY Example internal static class Program { private static UnityContainer unityContainer; private static SingleContactManagerForm singleContactManagerForm; private static void InitializeMainForm() { singleContactManagerForm = unityContainer.Resolve<SingleContactManagerForm>(); } } Inversion of Control – Service Locator http://www.martinfowler.com/articles/injection.html
- 35. Inversion of Control – Setter (Property) Injection // UNITY Example public class ContactManager : IContactManager { [Dependency] public IContactPersistence ContactPersistence { get { return this.contactPersistence; } set { this.contactPersistence = value; } } } http://www.martinfowler.com/articles/injection.html
- 36. Property Injection + Easy to understand - Hard to implement robust * Take if an good default exists - Limited in application otherwise
- 37. Method Injection public class ContactManager : IContactManager { …. public bool Save (IContactPersistencecontactDatabaseService, IContact contact) { if (logger == null) { throw new ArgumentNullException(“logger”); } …. // Additional business logic executed before calling the save return contactDatabaseService.Save(contact); } } http://www.martinfowler.com/articles/injection.html
- 38. Method Injection • Needed for handling changing dependencies in method calls
- 39. Ambient Context public class ContactManager : IContactManager { …. public bool Save (….) { …. IUser currentUser = ApplicationContext.CurrentUser; …. } } * The Ambient Context object needs to have a default value if not assigned yet.
- 40. Ambient Context • Avoids polluting an API with Cross Cutting Concerns • Only for Cross Cutting Concerns • Limited in application otherwise
- 41. The Adapter Pattern from Gang of Four, “Design Patterns”
- 42. Interception Public class LoggingInterceptor : IContactManager { public bool Save(IContact contact) { bool success; this. logger.Log(“Starting saving’); success = this.contactManager.Save(contact); this. logger.Log(“Starting saving’); return success; } } Public class ContactManager : IContactManager { public bool Save(IContact contact) { …. return Result } } * Note: strong simplification of what logically happens through interception.
- 43. Dependency Injection Container & more • Typically support all types of Inversion of Control mechanisms • Constructor Injection • Property (Setter) Injection • Method (Interface) Injection • Service Locator •.NET based DI-Container • Unity • Castle Windsor • StructureMap • Spring.NET • Autofac • Puzzle.Nfactory • Ninject • PicoContainer.NET • and more Related Technology: • Managed Extensibility Framework (MEF)
- 44. The “Must Read”-Book(s) http://www.manning.com/seemann/ by Mark Seemann Dependency Injection is a set of software design principles and patterns that enable us to develop loosely coupled code.
- 45. Summary Clean Code - DI Maintainability is achieved through: • Simplification, Specialization Decoupling (KISS, SoC, IoC, DI) • Dependency Injection Constructor Injection as default, Property and Method Injection as needed, Ambient Context for Dependencies with a default, Service Locator never • Registration Configuration by Convention if possible, exception in Code as needed Configuration by XML for explicit extensibility and post compile setup • Quality through Testability (all of them!) Graphic by Nathan Sawaya courtesy of brickartist.com
- 46. Downloads, Feedback & Comments: Q & A Graphic by Nathan Sawaya courtesy of brickartist.com [email protected] www.designitright.net http://speakerrate.com/ speakers /18667-theo-jungeblut
- 47. Time to say Thank You! The Organizers Evergreen Valley College (team) The volunteers (how about you?) TheSponsors Picturesfromhttp://blog.siliconvalley-codecamp.com
- 50. … thanks for you attention! And visit and support the www.siliconvalley-codecamp.com Please fill out the feedback, and… www.speakerrate.com/theoj