This document discusses design patterns and the model-view-controller (MVC) framework. It introduces common design patterns like singleton, strategy, and observer. It then explains the history and components of MVC, including how the view displays information to the user, the controller handles user input, and the model manages application data. The document emphasizes that design patterns and MVC help create extensible and maintainable code.

1. Design Patterns and MVC
Sway Wang
2014.12.25

2. Outline
• What is Design Pattern?
– Singleton pattern
– Strategy pattern
– Observer pattern
• What is MVC?
– C# example
– Ruby on Rails
• Conclusion

3. What is Design Pattern?
• Patterns are formalized best practices that the
programmer can use to solve common problems when
designing an application or system

4. The History of Design Pattern
• Christopher Alexander (1977)
• Kent Beck and Ward Cunningham (1987)
• Gamma, Erich; Richard Helm, Ralph Johnson,
and John Vlissides
– Design Patterns: Elements of Reusable Object-
Oriented Software (1995)

5. History

6. Gang of Four (GoF) Patterns
• Creational Patterns
(abstracting the object-instantiation process)
– Factory Method Abstract Factory
– Singleton Builder
– Prototype
• Structural Patterns
(how objects/classes can be combined to form larger structures)
– Adapter Bridge
– Composite Decorator
– Facade Flyweight
– Proxy

7. Gang of Four (GoF) patterns
• Behavioral Patterns
(communication between objects)
– Command Interpreter Iterator
– Mediator Observer State
– Strategy Chain of Responsibility Visitor
– Template Method

8. Singleton Pattern
• It restricts the instantiation of a class to
one object

9. Singleton Pattern(C#)

10. Is Your Singleton Broken?
• The singleton pattern must be carefully
constructed in multi-threaded applications
• [OSDC 2014] fr3@K - Is Your Singleton
Broken? - YouTube

11. Is Your Singleton Broken?
• The singleton pattern must be carefully
constructed in multi-threaded applications
• [OSDC 2014] fr3@K - Is Your Singleton
Broken? – YouTube
• Global variable issue

12. Strategy Pattern
• It enables an algorithm's behavior to be
selected at runtime

13. Strategy Pattern: Duck Example

14. Now We Need the Ducks to Fly

15. Now We Need the Ducks to Fly

16. Decoy Duck

17. How About a Interface?
Duplicate code

18. Strategy Pattern: Duck Example

19. Strategy Pattern: Duck Example

20. Strategy Pattern: Duck Example

21. Strategy Pattern: Duck Example

22. Strategy Pattern: Duck Example

23. Setting Behavior Dynamically

24. Strategy Pattern: Duck Example

25. Design Principle
多用合成，少用繼承

26. Open-Closed Principle(OCP)
Software entities (classes, modules,
functions, etc.) should be open for
extension, but closed for modification
一個軟體應該要夠開放使得它可以被擴充，
但是也要夠封閉以避免不必要的修改

27. Strategy Pattern
• It enables an algorithm's behavior to be
selected at runtime

28. Observer Pattern
• Newspaper subscription
• Publishers + Subscribers = Observer Pattern

29. Observer Pattern
• Newspaper subscription
• Publishers + Subscribers = Observer Pattern

30. Observer Pattern

31. Observer Pattern

32. Observer Example (C#)

33. Subject Example (C#)

34. Subject Example (C#)

35. The History of MVC
• MVC is really old and was first described in
1979 by Trygve Reenskaug
• Smalltalk at Xerox PARC.
• Today MVC is used in most modern web and
GUI frameworks

36. The History of MVC
• Ruby On Rails: A popular Ruby web-
framework
• Apple Cocoa: Apple's framework for
developing Mac OS and iOS applications
• ASP.Net Framework: Microsoft's web-
framework for implementing web applications
• ... And many many more languages and
frameworks

37. MVC

38. View

39. Controller

40. Model

41. Perl CGI – 計數器

42. PHP計數器

43. Ruby on Rails

44. 缺點
• HTML和邏輯綁在一起
• 網站規模變大後不易修改
• 難以分工
• Web Framework
– 導入OO概念
– 制定好了一套規範和慣例，讓開發者在該架構下來進行
開發

45. Web Framework
• 導入OO概念
• 制定好了一套規範和慣例，讓開發者在該架
構下來進行開發

46. Conclusion
• 要精通OOP一定要會Design Pattern
• Design Pattern三種境界
– 什麼東西都套pattern
– 知道什麼時候該用pattern
– KISS principle
• MVC架構的AP後續維護較容易
• 設計良好的程式碼當未來需求變更時，較容易改
變