SOLID Principles part 2
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Of the SOLID principles, made famous by Robert C. Martin, we'll discuss the Interface Segregation Principle and the Dependency Inversion Principle. This session will explain them thoroughly and give real life examples instead of the regular customer & order examples. You'll walk away knowing what the benefits are and how to use them properly.
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SOLID Principles part 2
- 1. Dennis van der Stelt Interface Segregation Principle Dependency Inversion Principle Dennis van der Stelt Software Architect Tellus http://bloggingabout.net/blogs/dennis/ @dvdstelt dvdstelt@tellus.com Pascal de Jonge Development Lead Tellus http://www.pazquality.com/ @pdejonge pdejonge@tellus.com SOLID
- 2. Dennis van der Stelt
- 3. Dennis van der Stelt AGENDA
- 4. Dennis van der Stelt SOLID History
- 5. Dennis van der Stelt Guidance
- 6. Dennis van der Stelt SOLID Five principles Single Responsibility SOLID Open/Closed Liskov Substitution Interface Segregation Learn them, love them, live by them… Dependency Inversion
- 7. Dennis van der Stelt SOLID Books
- 8. Dennis van der Stelt SOLID Interface Segregation Principle
- 9. Dennis van der Stelt INTERFACE SEGREGATION PRINCIPLE clients should not be forced to depend on methods they do not use
- 10. Dennis van der Stelt INTERFACE SEGREGATION PRINCIPLE tailor interfaces to individual client’s needs
- 11. Dennis van der Stelt DEMO Membership Provider
- 12. Dennis van der Stelt INTERFACE SEGREGATION PRINCIPLE public interface IVerifyCredentials { int MaxInvalidPasswordAttempts { get; } bool ValidateUser(string username, string password); } public interface IManageCredentials { bool ChangePassword(string oldPassword, string newPassword); int MinRequiredNonAlphanumericCharacters { get; } int MinRequiredPasswordLength { get; } string ResetPassword(string username); } public interface IManageUsers { MembershipUser CreateUser(string username, string password); bool DeleteUser(string username, bool deleteAllRelatedData); }
- 13. Dennis van der Stelt INTERFACE SEGREGATION PRINCIPLE Why is violation of this principle a problem? introduces very fat interfaces difficult to extend functionality violates single responsibility principle forced dependencies 02 03 04 01
- 14. Dennis van der Stelt public interface IDoor { bool IsDoorOpen { get; set; } void Lock(); void Unlock(); } INTERFACE SEGREGATION PRINCIPLE public class SimpleDoor : IDoor { public bool IsDoorOpen { get; set; } public void Lock() { // Implementation here... } public void Unlock() { // Implementation here... } }
- 15. Dennis van der Stelt public interface ITimerFunction { void TimerFunction(); } INTERFACE SEGREGATION PRINCIPLE class AdvancedDoor : IDoor, ITimerFunction { public bool IsDoorOpen { get; set; } public void Lock() { } public void Unlock() { } public void TimerFunction() { // Implementation here... } }
- 16. Dennis van der Stelt List<IDoor> doors = new List<IDoor>() { new SimpleDoor(), new AdvancedDoor() }; foreach (var door in doors) { if (door is ITimerFunction) ((ITimerFunction)door).TimerFunction(); } INTERFACE SEGREGATION PRINCIPLE
- 17. Dennis van der Stelt SOLID Dependency Inversion Principle
- 18. Dennis van der Stelt DEPENDENCY INVERSION PRINCIPLE high level modules should not depend upon low level modules, both should depend on abstractions. abstractions should not depend upon details. details should depend on abstractions
- 19. Dennis van der Stelt DEPENDENCY INVERSION PRINCIPLE Inversion of control Component A Component B Component C
- 20. Dennis van der Stelt DEPENDENCY INVERSION PRINCIPLE Inversion of control Component A Component A Service <<interface>> Component B Component A Service Component C <<interface>>
- 21. Dennis van der Stelt DEPENDENCY INVERSION PRINCIPLE Inversion of control Component A Client Service <<interface>> Component B Component A Service Component C <<interface>> Component D
- 22. Dennis van der Stelt DEPENDENCY INVERSION PRINCIPLE Valar Morghulis
- 23. Dennis van der Stelt DEMO Game on!!!
- 24. Dennis van der Stelt DEPENDENCY INVERSION PRINCIPLE Violations public class SecurityService { public static User GetCurrentUser() { return Context.User; } } Dependency in static method
- 25. Dennis van der Stelt DEPENDENCY INVERSION PRINCIPLE Violations public class OrderProcessing { private IList<Product> FindProduct(int category) { var repository = new ProductRepository(); return repository.FindByCategory(category); } } Instantiating your own dependencies
- 26. Dennis van der Stelt DEPENDENCY INVERSION PRINCIPLE Violations public class OrderProcessing { private IList<Product> FindProduct(int category) { var repository = ServiceLocator.GetInstance<IProductRepository>(); return repository.FindByCategory(category); } } Asking for instantiating your dependencies only at the composition root
- 27. Dennis van der Stelt COMPOSITION ROOT Application entry point Factory Pattern Libraries & Frameworks
- 28. Dennis van der Stelt COMPOSITION ROOT Application entry point Factory Pattern Libraries & Frameworks
- 29. Dennis van der Stelt COMPOSITION ROOT Application entry point Factory Pattern Libraries & Frameworks
- 30. Dennis van der Stelt DEPENDENCY INVERSION PRINCIPLE Inversion of control HomeController ICustomer Registration <<interface>> Customer Registration IMessageSender Factory MessageSender Factory <<interface>> ICustomer Repository <<interface>> Customer Repository MessageSender Base
- 31. Dennis van der Stelt DEMO Dependency Injection in MVC
- 32. Dennis van der Stelt
- 33. Dennis van der Stelt CONCLUSION Single Responsibility SOLID Open/Closed Liskov Substitution Interface Seggregation Dependency Inversion
- 34. Dennis van der Stelt34 Thank you questions? Dennis van der Stelt Software Architect Tellus http://bloggingabout.net/blogs/dennis/ @dvdstelt dvdstelt@tellus.com Pascal de Jonge Development Lead Tellus http://www.pazquality.com/ @pdejonge pdejonge@tellus.com
Notas do Editor
- There are other talks that will go into Big Data and Hadoop so we’ll only do a quick overview of that right now. We’ll spend most of our time on Hive.
- 5 basic principles of OOPDIntroduced in 2000By Robert C. Martin (Uncle Bob)Whenapplied, more likelyto have a bettermaintainableandextendable system over time.
- Guidelines, not hard rules, not a dogmaUse common senseDon’tjustthrowthemaway
- Add “System.Web.Applications” and implement “MembershipProvider”
- Also doesn’t violate SRP
- NotImplementedException
- Also doesn’t violate SRP
- Also doesn’t violate SRP
- Also doesn’t violate SRP
- Interfaces are packaged with higher-level components. They define higher-level components needs, not lower-level components behavior.
- Tight coupling- When 2 classes depend on each other