"Refactoring to SOLID Code" session presentation from Emerging .NET Devs - October 2011 User Group Meeting. Please note that this presentation has been simplified for publishing.

1. Emerging .NET Devs
October User Group Meeting
Design Principles &
Practices
Adil Ahmed Mughal
Zubair Ahmed

2. Refactoring to SOLID Code
Emerging .NET Devs

3. Session => Refactoring to SOLID Code
What You must already know:
- Object Oriented Programming Language such as Java, C++, C#
- Professional Experience
What You will learn today:
- Good Practices
- OO Principles
Sponsors:

4. Speaker => Adil Ahmed Mughal
Affiliations:
Contact Information:
adil.mughal@live.com
@adilamughal
http://www.adilmughal.com

5. Agenda
This is not a single side talk, its discussion!
Promise me that you will raise hand when you have query?
• How You Code Today?
• What is Bad Design?
• What would You Call a Good Design?
• SOLID Principles!

6. How You Code Today?
• Do you care about design principles or patterns?
• Anti-patterns?
• Is your code Agile?
• Do you Refactor your code?
• Is your code design bad or good?

8. Bad design is...
Needless
Rigid
Complexity
Needless
Fragile
Repetition
Immobile
Viscous

11. What would You Call a Good Design?
• Reliability
• Flexibility
• Separations of Concerns
• Reusability
• Maintainability

12. SOLID
Object Oriented Principles
Introduced by Robert C. Martin in
early 2000s

13. SOLID Principles
• S – Single Responsibility Principle (SRP)
• O – Open Closed Principle (OCP)
• L – Liskov Substitution Principle (LSP)
• I – Interface Segregation Principle (ISP)
• D – Dependency Inversion Principle (DIP)

14. Single Responsibility Principle
(SRP)

16. The Single Responsibility Principle
"A responsibility is a reason to change, a class or
module should have one, and only one, reason
to change."

17. The Single Responsibility Principle
• “There should never be more than one reason for a
class to change.”
• More responsibilities => More likelihood of change
• Dijkstra’s SoC: separation of concerns
• Applies on every level of code
• Solves the naming dilemma

18. Trade Validator
Trade
Validator
DB
Trade
What is wrong here: Changes if DB
changes or Business Logic Changes

19. Refactored Trade Validator
Trade Trade
Validator Source
Trade
DB
What's its job?
Classes must have an identifiable single
responsibility.

21. The Open-Closed Principle (OCP)

22. The Open Closed Principle
“Software Entities (Classes, Modules, Functions,
etc.) should be open for extension, but closed for
modification”

23. The Open Closed Principle
• Modules that conform to the open-closed principle have
two primary attributes
– Open For Extension
• behavior of the module can be extended
– Closed for Modification
• The source code of such a module is inviolate
• The normal way to extend the behavior of a module is to
make changes to that module. How can these two opposing
attributes be resolved?

24. OCP – Change behavior without
changing code?
• Abstraction is the key to achieve it
Client Server
Closed Client

25. OCP – Change behavior without
changing code?
Client Abstract
Server
Server
Open Client

27. Liskov Substitution Principle
(LSP)

28. Liskov Substitution Principle
“Functions that reference a base class must be
able to use objects of derived classes without
knowing it."

30. Interface Segregation Principle
(ISP)

31. Interface Segregation Principle
“Clients should not be forced to depend upon
interfaces that they do not use.”
• Prefer small, cohesive interfaces to fat
interfaces

33. Dependency Inversion Principle
(DIP)

34. Dependency Inversion Principle
“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.”

35. Trade Validator
Introduce stability
High Level (Less Stable) with abstraction
Trade Trade
Validator Source
Trade
Low Level DB
(More Stable)

36. Better Trade Validator
Trade Validator
<Interface>
ITradeSource
Trade DbTradeSource
DB

37. Extensible Trade Validator
<Interface>
TradeValidator ITradeSource
Trade DbTradeSource WSTradeSource
DB
Cloud

39. DEMO
Let’s Refactor!

40. Actions => From Now On
Learn, Practice and Make it your Habit
Links:
- ObjectMentor.com
- Practices and Patterns on MSDN
Books:

41. References
• Combatting Software Entropy using Design Principles
and Practices – Hammad Rajjoub – TechEd ME
• Agile Principles, Patterns and Practices using C# by
Robert.C.Martin
• Special thanks for motivational poster images by
NimblePros

42. Thank You!
Refactoring to SOLID Code
Emerging .NET Devs