Introduction to Design Patterns

Motivating developers to learn about design patterns.

Transcript

1. Intro to Design Patterns Zaki Shaheen
2. Agenda • What is “design”? • What is “pattern”? • Motivation for design patterns • “The pattern language” • Brief intro to GoF Design Patterns • How to learn design patterns • Summary + QnA
3. What is “design”? "I think there is a profound and enduring beauty in simplicity; in clarity, in efficiency. True simplicity is derived from so much more than just the absence of clutter and ornamentation. It's about bringing order to complexity." - Sir Johnathan Ive, Apple SVP of Industrial design.
4. "a specification of an object, manifested by an agent, intended to accomplish goals, in a particular environment, using a set of primitive components, satisfying a set of requirements, subject to constraints;" “Form follows function”
5. Quiz: Which one is “design”? VS
6. What is “pattern”? • recurrence of a phenomenon (activity, event, problem, solution, situation) ◦ explicit recurrence (Bathing, city centers, wanting to write) ◦ implicit recurrence (relationships, building entrance, screw drivers?)
7. Motivation for design patterns • Patterns are everywhere and so is design • The Pattern language by Christopher Alexander (1977) • Art of War by Sun Tzu. (300-500 BC)
8. “The pattern language” • 253 patterns for towns, buildings and construction • Towns (Ring roads, web of shopping, network of learning, green streets, graveyards) • Buildings (south facing outdoors, indoor sunlight, fire place) • Construction (box columns, stair vault, floor surface, colors)
9. "The street cafe provides a unique setting, special to cities: a place where people can sit lazily, legitimately, be on view, and watch the world go by... Encourage local cafes to spring up in each neighborhood. Make them intimate places, with several rooms, open to a busy path, where people can sit with coffee or a drink and watch the world go by. Build the front of the cafe so that a set of tables stretch out of the cafe, right into the street." https://www.patternlanguage.com/labyrinth/apl-tour2.html
11. (Brief) introduction to GoF • Software architecture patterns • “Design Patterns: Elements of Reusable Object-Oriented Software” • Creational / Structural / Behavioral
12. Creational Design Patterns • Singleton ◦ UIApplication, UIWindow, zend_controller_front • Object pool ◦ Reusable cells in UITableView, photo controller, carousels
13. Structural Design patterns • Composite ◦ The “V” in MVC. ◦ View hierarchy ◦ Could be your REST representation. • Adapter • Decorator • Flyweight
14. Behavioral Patterns • Observer ◦ NSNotification System ◦ ServiceManager, EventManager (in ZF2) ◦ Also called pub-sub • Chain of responsibility ◦ UIResponder chain • Command ◦ NSInvocation • Iterator ◦ Enumerators
15. Other Cocoa specific patterns • Delegation • Block Delegation • Target-Action
16. Quiz: Is MVC a design pattern? • Model • View • Controller
17. Other patterns • Enterprise Architecture Patterns ◦ Gateway ◦ Mapper ◦ Front Controller ◦ Active Record ◦ http://martinfowler.com/eaaCatalog/ • SOA Patterns (http://www.soapatterns.org) • Cloud Patterns ◦ Load balancing, clustering, naming, provisioning ◦ http://cloudpatterns.org
18. • What about your own design patterns? • Service layer pattern? • Viper Architecture?
19. Tips on learning patterns • Requires deep, focused and abstract thinking • No use without solid OOP principles and design thinking/practice • No use without learning UML • No use without experience of problems • Read the GoF book • Think abstractly, profoundly, retrospectively • Start with birds eye view • Learn creational, structural and behavioral in that order. • Don't restrict yourself to GoF Book • Don't restrict yourself to other people's patterns
20. Key takeaways • Design is not art. • Patterns are everywhere, requires deep abstract thinking to find them. • Design patterns give a vocabulary to tackle “design” problems.
21. Resources • The web is full of information • http://sourcemaking.com/design-patterns-and-tips • Several books, ask me if you are interested.
22. Quiz • Identify a pattern • Argue about design • Think of a design pattern
23. Question and Answers