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Design Patterns

Design Patterns. Now you are ready for Design Patterns.

ashely-burks
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Design Patterns

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  1. Design Patterns

  2. Now you are ready for Design Patterns • Design patterns are recurring solutions to software design problems you find again and again in real-world application development. Patterns are about design and interaction of objects, as well as providing a communication platform concerning elegant, reusable solutions to commonly encountered programming challenges. • The Gang of Four (GoF) patterns are generally considered the foundation for all other patterns. They are categorized in three groups: Creational, Structural, and Behavioral.

  3. Observer pattern(behavioral) • Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. • http://www.dofactory.com/Patterns/PatternObserver.aspx#_self2

  4. This is the class diagram from the Observer Pattern Example

  5. When would I use the Observer Pattern? • When you want to notify Investor objects of a change in a Stock object (say the price changed) • When you want to notify Avatar objects of a change in a Boss object (say the boss is loosing health and you want to make sure all the avatars trying to kill him are notified)

  6. Singleton Pattern(creational) • Ensure a class has only one instance and provide a global point of access to it. • http://www.dofactory.com/Patterns/PatternSingleton.aspx#_self2

  7. Singleton Pattern Example Class Diagram

  8. When would l use the Singleton Pattern? • LoadBalancing object • Only a single instance (the singleton) of the class can be created because servers may dynamically come on- or off-line • every request must go through the one object that has knowledge about the state of the (web) farm. • A game service is a game component that uses an interface to enforce a singleton pattern and make a single instance of a game component accessible to all other components • A game service is a built in mechanism that allows a game to create and manage a single instance of a component and allows other components access to the service. • Good candidates for a game service are. • InputHandler • GameConsole • Profiling Service • Scoreboard • Gamer Services in the XNA Framework • http://msdn.microsoft.com/en-us/library/microsoft.xna.framework.gamerservices.aspx

  9. Factory Method Pattern(creational) • Creates an instance of several derived classes • Define an interface for creating an object, but let subclasses decide which class to instantiate. • Factory Method lets a class defer instantiation to subclasses.

  10. Here is the class diagram

  11. When would I use the factory pattern? Website factory Enemy factory So that you could have several different enemies in a game • For a myspace or facebook type of application

  12. How would I make levels in my game?

  13. The answer is a pattern • The abstract factory pattern • Creates an instance of several families of classes • Provide an interface for creating families of related or dependent objects without specifying their concrete classes.

  14. Class Diagram for the Abstract Factory

  15. Homework • Start working on your Design Patterns Presentation (this is due at the end of the semester) • Study for the midterm (next week) • Finish(work on) your game. (this is due after spring break) • Read DesignPatterns-TheIndieStoneCommunity.pdf

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