ActionScript 3.0 design patterns

523 Pages·2007·2.339 MB·English

by  William B Sanders, Chandima Cumaranatunge

ActionScript 3.0 Design Patterns
William B. Sanders and
Chandima Cumaranatunge
Beijing • Cambridge • Farnham • Köln • Paris • Sebastopol • Taipei • Tokyo
ActionScript 3.0 Design Patterns
by William B. Sanders and Chandima Cumaranatunge
Copyright © 2007 O’Reilly Media, Inc. All rights reserved.
Printed in the United States of America.
Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.
O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions
are also available for most titles (safari.oreilly.com). For more information, contact our
corporate/institutional sales department: [phone] [email protected].
Editor: Steve Weiss Indexer: John Bickelhaupt
Developmental Editor: Robyn G. Thomas Cover Designer: Karen Montgomery
Production Editor: Philip Dangler Interior Designer: David Futato
Copyeditor: Sohaila Abdulali Illustrators: RobertRomanoandJessamynRead
Printing History:
July 20007: First Edition.
Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks of
O’Reilly Media, Inc. ActionScript 3.0 Design Patterns, the image of a rosy feather starfish, and related
trade dress are trademarks of O’Reilly Media, Inc.
Manyofthedesignationsusedbymanufacturersandsellerstodistinguishtheirproductsareclaimedas
trademarks. Where those designations appear in this book, and O’Reilly Media, Inc. was aware of a
trademark claim, the designations have been printed in caps or initial caps.
While every precaution has been taken in the preparation of this book, the publisher and authors
assume no responsibility for errors or omissions, or for damages resulting from the use of the
information contained herein.
This book uses RepKover™, a durable and flexible lay-flat binding.
ISBN-10: 0-596-52846-9
ISBN-13: 978-0-59652846-1
[M]
Table of Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
Part I. Constant Change
1. Object-Oriented Programming, Design Patterns, and ActionScript 3.0 . . . . . 3
The Pleasure of Doing Something Well 3
OOP Basics 10
Abstraction 11
Encapsulation 15
Inheritance 24
Polymorphism 34
Principles of Design Pattern Development 42
Program to Interfaces over Implementations 45
Favor Composition 49
Maintenance and Extensibility Planning 57
Your Application Plan: It Ain’t You Babe 60
Part II. Creational Patterns
2. Factory Method Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
What Is the Factory Method Pattern? 65
Abstract Classes in ActionScript 3.0 68
Minimalist Example 69
Hiding the Product Classes 73
Example: Print Shop 74
Extended Example: Color Printing 80
Key OOP Concepts Used in the Factory Method Pattern 84
vii
Example: Sprite Factory 84
Example: Vertical Shooter Game 90
Summary 100
3. Singleton Pattern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
What Is the Singleton Pattern? 101
Key OOP Concepts Used with the Singleton Pattern 102
Minimalist Abstract Singleton 105
When to Use the Singleton Pattern 112
Summary 125
Part III. Structural Patterns
4. Decorator Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
What Is the Decorator Pattern? 129
Key OOP Concepts Used with the Decorator Pattern 132
Minimalist Abstract Decorator 135
Applying a Simple Decorator Pattern in Flash: PaperDoll 141
Decorating with Deadly Sins and Heavenly Virtues 148
Dynamic Selection of Concrete Components and Decorations:
A Hybrid Car Dealership 164
Summary 176
5. Adapter Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
What Is the Adapter Pattern? 177
Object and Class Adapters 179
Key OOP Concepts in the Adapter Pattern 185
Example: Car Steering Adapter 185
Extended Example: Steering the Car Using a Mouse 193
Example: List Display Adapter 194
Extended Example: Displaying the O’Reilly New Books List 199
Summary 203
6. Composite Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
What Is the Composite Pattern? 204
Minimalist Example of a Composite Pattern 207
Key OOP Concepts in the Composite Pattern 217
Example: Music Playlists 217
Example: Animating Composite Objects Using Inverse Kinematics 222
viii | Table of Contents
Using Flash’s Built-in Composite Structure: theDisplayList 233
Summary 243
Part IV. Behavioral Patterns
7. Command Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
What Is the Command Pattern? 247
Minimalist Example of a Command Pattern 251
Key OOP Concepts in the Command Pattern 255
Minimalist Example: Macro Commands 255
Example: Number Manipulator 258
Extended Example: Sharing Command Objects 263
Extended Example: Implementing Undo 266
Example: Podcast Radio 270
Extended Example: Dynamic Command Object Assignment 276
Summary 281
8. Observer Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
What Is the Observer Pattern? 282
Key OOP Concepts Used with the Observer Pattern 285
Minimalist Abstract Observer 289
Example: Adding States and Identifying Users 294
Dynamically Changing States 302
Example: Working with Different Data Displays 318
Summary 330
9. Template Method Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
What Is the Template Method Pattern? 331
Key OOP Concepts Used with the Template Method 335
Minimalist Example: Abstract Template Method 338
Employing Flexibility in the Template Method 341
Selecting and Playing Sound and Video 344
Hooking It Up 351
Summary 356
10. State Pattern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
Design Pattern to Create a State Machine 357
Key OOP Concepts Used with the State Pattern 360
Minimalist Abstract State Pattern 361
Table of Contents | ix
Video Player Concrete State Application 367
Expanding the State Design: Adding States 374
Adding More States and Streaming Capabilities 382
Summary 397
11. Strategy Pattern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
What Is the Strategy Pattern? 398
Key OOP Concepts Used with the Strategy Pattern 400
Minimalist Abstract State Pattern 402
Adding More Concrete Strategies and Concrete Contexts 406
Working with String Strategies 414
Summary 423
Part V. Multiple Patterns
12. Model-View-Controller Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
What Is the Model-View-Controller (MVC) Pattern? 427
Communication Between the MVC Elements 428
Embedded Patterns in the MVC 430
Minimalist Example of an MVC Pattern 431
Key OOP Concepts in the MVC Pattern 443
Example: Weather Maps 443
Extended Example: Infrared Weather Maps 451
Example: Cars 457
Custom Views 463
Adding a Chase Car 466
Summary 468
13. Symmetric Proxy Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
Simultaneous Game Moves and Outcomes 469
The Symmetric Proxy Pattern 473
Key OOP Concepts Used with the Symmetric Proxy 475
The Player Interface 477
The Referee 478
Information Shared Over the Internet 483
Player-Proxy Classes 486
Classes and Document Files Support 494
Summary 498
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499
x | Table of Contents
Preface
1
AsActionScripthasevolvedfromafewstatementsinFlashtoafull-fledgedInternet
programming language in the latest release of Flash and Flex, we have the ability to
implement sophisticated designs developed for languages using object-oriented pro-
gramming (OOP). ActionScript 3.0 heralds a new era in Flash and Flex program-
ming because it implements the ECMAScript standard for Internet languages. Many
features found in languages such as C++ and JavaTM are now available in Action-
Script 3.0.
AlongwithmoresophisticatedfeaturesinActionScript3.0comemoresophisticated
ways of programming and thinking about programming. Most readers of this book
willbefamiliarwithOOPtosomedegree,andlikethestepfromsequentialorproce-
duralprogrammingtoOOP,thesteptodesignpatternprogrammingisastepupfor
OOP programmers. We felt that because ActionScript 3.0 had arrived at a point
where more complex and challenging programming structures can be developed,
FlashandFlexprogrammersneededtounderstandprogrammingtechniquestocope
with these structures.
Byunderstandingdesignpatternprogramming,youwillbeabletowritebetterOOP
code,andreusethatcodeinotherprograms.Thebetterpayingpositionsinthepro-
gramming field favor those developers who can work with team development, and
the sophisticated structures that design patterns and OOP were developed to han-
dle.Atthesametimethatyougainproficiencyinprogrammingmorecomplexappli-
cations, design patterns actually make programming easier. In large and complex
applications, programmers have the most difficulty with poor planning and awk-
warddesignstructures.Designpatternsnotonlyprovidesolutionsforcommonchal-
lenges,butalsofocusonmaintenanceandchange.Thevocabularyofdesignpatterns
is equally important because with it, you can become part of the developer commu-
nity that communicates clearly in the language of design patterns.
xi
Who This Book Is For
We wanted to develop a book for intermediate to advanced ActionScript 3.0 users.
Unlike some languages, such as Java, where the readers are likely to have computer
science or computer engineering degrees, most ActionScript 3.0 users are likely to
have learned ActionScript in developmental stages using Flash. As a result, their
backgroundsarefarmorevaried,andtheprogrammingbaselessdefinite.We’resure
that a number of ActionScript programmers have computer science or related back-
grounds, and much of the introductory materials in the first chapter will be redun-
dant.Likewise,we’recertainthatsomereadersonthelowerendoftheintermediate
levelarelearningobject-orientedprogrammingatthesametimethatthey’retryingto
pick up design patterns; they may have little or no formal training in programming.
Given the range of ActionScript programming backgrounds, we’re bound to be too
difficult for some and too simplistic for others. However, this book’s overall goal is
to explain how to use different design patterns. We targeted whom we considered
intermediatelevelActionScriptdevelopers.We’veprovidedeverythingtheintermedi-
ate level developer will need to move to the advanced level. For the advanced user,
we provide explanations and examples of how to use design patterns with Action-
Script 3.0.
How This Book Is Organized
Thebook’sorganizationreflectsthetopicorganizationfoundinDesignPatternsEle-
ments of Reusable Object-Oriented Software by Erich Gamma, Richard Helm, Ralph
Johnson, and John Vlissides (Addison-Wesley, 1995).
The first part contains Chapter1, which is an introduction to design patterns. We
added an introductory section for readers with minimal object-oriented program-
mingexperience.MoreadvancedusersmaywanttoskipthereviewofOOP,butgo
over the materials on design patterns.
Part I,Constant Change
Chapter1,Object-Oriented Programming, Design Patterns, and ActionScript 3.0
PartsII,IIIand,IVarethethreemajorpartsofthebook.Theyexaminefundamental
design patterns, and organize the patterns into creational, structural and behavioral
categories. Representative design patterns are included in each part, but we didn’t
include every single design pattern from the book by Gamma and his associates.
Part II,Creational Patterns
Chapter2,Factory Method Pattern
Chapter3,Singleton Pattern
xii | Preface
Part III,Structural Patterns
Chapter4,Decorator Pattern
Chapter5,Adapter Pattern
Chapter6,Composite Pattern
Part IV,Behavioral Patterns
Chapter7,Command Pattern
Chapter8,Observer Pattern
Chapter9,Template Method Pattern
Chapter10,State Pattern
Chapter11,Strategy Pattern
Part V contains two chapters on using multiple design patterns in application devel-
opment.TheModel-View-ControllerandSymmetricProxydesignsincorporatemore
thanasingledesignpattern.They’reorganizedliketheotherchaptersondesignpat-
terns as far as explaining how the multiple patterns work. However, the multiple
designs rely more on object diagrams than class diagrams.
Part V,Multiple Patterns
Chapter12,Model-View-Controller Pattern
Chapter13,Symmetric Proxy Pattern
Each chapter on design patterns is organized to optimize and clarify understanding
the purpose of a design pattern and how to use it. The following sections, although
not necessarily in this order, can be found in each of the chapters on design patterns:
• What is the pattern?
• Key features of the pattern
• The formal model of the pattern including a class diagram
• Key OOP concepts found in the pattern
• Minimalist abstract example
• Applied examples
We organized the book in this manner to provide a well-rounded picture of each
design pattern. By explaining the pattern and its key features, we focus on the pat-
tern’s function and structure. The formal model and class diagram gives a wider
overview, so you can see the structure and the interconnected classes and interface.
We also included certain key OOP concepts for the different patterns. We did this
for two reasons. First, the intermediate user will be better able to understand the
OOP concept at work, and so understand OOP better. Second, we hoped that
advanced users could see the concepts as shorthand to quickly determine how the
design pattern is structured.
Preface | xiii
What You Need to Use This Book
YouwillneedeitherFlashCS3orFlex2toworkwiththeprogramexamplesinthis
book.AlltheapplicationsweredevelopedintheFlashIDE,soFlex2developerswill
need to make modifications, especially where certain features were developed using
Flash drawing tools and components.
A few examples use Flash Media Server 2 (FMS2). The examples using FMS2 can be
createdusingtheDeveloper’sversionofFMS2andcanbefreelydownloadedathttp://
www.adobe.com/downloads/. You will need either a Windows or Linux OS to run
FlashMediaServer2.Ifyouhavea“MacTel”Macintosh,youcanusetheWindowOS
torunFMS,butifyouhaveanolderMacintoshrunningontheMotorolaCPU,you’ll
need to have a LAN or Internet access to a Windows or Linux platform running
FMS2. Alternatively, you can skip the examples with FMS2.
Say It Again, Sam
One thing we can guarantee is redundancy. We know that people have different
styles of learning. Some are conceptual learners, some experiential, and some meta-
phorical or any combinations of those, plus others we haven’t heard about yet. So
you will see that we use several different ways to say the same thing with the idea
that if you don’t get it one way, you’ll get it another.
At the same time, we feel that by discussing the same idea or concept in different
ways and in different contexts, the specific sense of that concept is better shaped. In
looking over reference materials published in books, articles, and online regarding
Design Patterns, we found that some materials were not quite accurate in depicting
some features. We worked very hard not to make mistakes, and so by providing
numerous contexts, we can help filter out what we specifically mean, and, equally
important, what we don’t mean. The ultimate authority is always Design Patterns:
Elements of Reusable Object-Oriented Software, and if you have any questions about
exactly what we mean, you can always check it out at the original source.
Over the years, a number of articles, books, dissertations and other treatises have
appeared offering suggestions for improving the original design patterns. Some of
thesedocumentsarequiteuseful,andevenhavetheendorsementofmembersofthe
Gang of Four (GoF)—Erich Gamma, Richard Helm, Ralph Johnson, and John Vlis-
sides. Others are not too useful, especially for learning design patterns, and tend to
complicate an already complex subject. As a result, we have not strayed from the
path laid down in the original text by GoF.
xiv | Preface