This document discusses dependency injection and inversion of control containers. It explains that dependency injection means passing instance variables into a class rather than having the class create its own dependencies. This improves testability and loose coupling between classes. Inversion of control containers can manage dependencies and make dependency injection easier by automatically resolving dependencies. The document provides examples of configuring dependencies using an inversion of control container to handle instantiating classes and their dependencies.

1. Dependency InjectionAnd using an Inversion of Control (IoC) container

2. What is Dependency InjectionGiving an object instance it’s variables

3. Dependency Non-Injectionpublic class Whatever{ private DbStuff _db;  This is a variable public Whatever() { _db = new DbStuff();  And Whatever } depends on itso it creates it public void DoIt() { _db.GetData(); }}

4. And this is bad for all kinds of reasons…

5. Single Responsibility PrincipleA class should have one, and only one, reason to change.We switch from SQL Server to Oracle and our Whatever class needs to change

6. Dependency Injectionpublic class Whatever{ private DbStuff_db; public Whatever(DbStuff database) { _db = database;  The ‘new’ keyword } is outta there public void DoIt() { _db.GetData(); }}

7. WinOur Whateverclass still depends on DbDatabut it is not responsible for itBy adhering to SRP through dependency injection we increasecohesion

8. But wait! We still have a problem

9. Dependency Inversion PrincipleDepend on abstractions, not on concretions.We can improve the situation by depending on an interface or abstract class

10. Dependency Injection v 2.0public class Whatever{ private IDbStuff _db;  Better public Whatever(IDbStuff database) { _db = database;  life is good } public void DoIt() { _db.GetData(); }}

11. To summarize, DI is about passing instance variables

12. BenefitsHigh cohesion because classes are focused on doing one thing really wellTestabilityIDbStuff data = new FakeDbWithBadData();var test = new Whatever(data);Assert.Throws(Exception,test.DoIt());The class under test did not have to change. Magic!

13. private readonlySystemConfiguration _configuration;private readonlyIWorkorderEntityBuilder _entityBuilder;public NewEntityWorkorderManager(IWorkorderRepositoryworkorderRepository,IMessageRepositorymessageRepository,IWorkorderEntityBuilderentityBuilder,SystemConfiguration configuration,ICityworksRepositorycityworksRepository): base(workorderRepository, messageRepository,cityworksRepository, configuration) { _entityBuilder = entityBuilder; _configuration = configuration; }

14. Inversion of Control Containers(IoC is a terrible term but we’re stuck with it. But maybe we’ll use container instead. At least it’s shorter.)

15. Manage DependenciesDI makes for cohesive, loosely couple softwareBut also more moving partsIoC containers exist to make dependency injection easier and more predictable

16. ContainersA Short ListSpringSpring.NETPicoCastle WindsorStructureMapNinjectAutofacUnityGlassfish and any EJB 3.0 app server

17. Workflow

18. ForRequestedType<ISpatialQuery>() .TheDefaultIsConcreteType<SpatialQueryGenericClient>();

19. ForRequestedType<ISettingRepository>() .TheDefault.Is.OfConcreteType<ApplicationSettingRepository>() .CtorDependency<IUnitOfWork>("unitOfWork") .Is(u => u.TheInstanceNamed(Resources.WCSDatasource));

20. var settings = ObjectFactory.GetInstance<ISettingRepository>();

21. Autowiring Is A Big Win

22. Things depend on things depend on things…varprocessor = ObjectFactory.GetInstance<IMessageProcessor>();

23. FeaturesMany other features but that’s the coreManage lifetime of objectsSingleton, per-thread, per-sessionXML configuration