MACROMEDIA FLEX-FLEX ACTIONSCRIPT LANGUAGE Manuale di servizio

Flex ActionScript Language Reference

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Acknowledgments

Project Management: Barbara Herbert, Stephen Gilson

Writing: Jody Bleyle, Mary Burger, Kim Diezel, Stephen Gilson, Stephanie Gowin, Dan Harris, Barbara Herbert, Matt Horn,

Barbara Nelson, Shirley Ong, Michael Peterson, Tim Statler

Managing Editor: Rosana Francescato

Editing: Linda Adler, Mary Ferguson, Mary Kraemer, Noreen Maher, Antonio Padial, Lisa Stanziano, Anne Szabla

Production Management: Patrice O’Neill

Media Design and Production: Adam Barnett, Christopher Basmajian, Aaron Begley, John Francis

Second Edition: November 2004

Macromedia, Inc.

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San Francisco, CA 94103

CONTENTS

INTRODUCTION: Getting Started with ActionScript . . . . . . . . . . . . . . . . . . . . . . . 5

Intended audience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Using the documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Typographical conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Terms used in this document. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Additional resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

PART I: Welcome to ActionScript

CHAPTER 1: ActionScript Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Differences between ActionScript and JavaScript . . . . . . . . . . . . . . . . . . . . . . . . . 10

Unicode support for ActionScript . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

About data types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Assigning data types to elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

About variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Using operators to manipulate values in expressions . . . . . . . . . . . . . . . . . . . . . . . 31

Using condition statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Using built-in functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Creating functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

CHAPTER 2: Creating Custom Classes with ActionScript 2.0 . . . . . . . . . . . . . . . 45

Principles of object-oriented programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Using classes: a simple example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Creating and using classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Creating dynamic classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Using packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Creating and using interfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Instance and class members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Implicit getter/setter methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Understanding the classpath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Importing classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

4 Contents

CHAPTER 3: Working with External Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Sending and loading variables to and from a remote source . . . . . . . . . . . . . . . . . . 67

Sending messages to and from Flash Player . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

PART II: Reference

CHAPTER 4: About the ActionScript Language Reference . . . . . . . . . . . . . . . . . 77

Sample entry for most ActionScript elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Sample entry for classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

CHAPTER 5: ActionScript Core Language Elements. . . . . . . . . . . . . . . . . . . . . . 80

CHAPTER 6: ActionScript Core Classes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232

CHAPTER 7: ActionScript for Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490

APPENDIX A: Deprecated Flash 4 operators . . . . . . . . . . . . . . . . . . . . . . . . . . . 809

APPENDIX B: Keyboard Keys and Key Code Values . . . . . . . . . . . . . . . . . . . . . 811

Letters A to Z and standard numbers 0 to 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 811

Keys on the numeric keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813

Function keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813

Other keys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817

INDEX OF LANGUAGE ELEMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823

INTRODUCTION

Getting Started with ActionScript

Macromedia Flex developers can use ActionScript to extend the functionality of their Flex

applications. ActionScript is an ECMAScript-based language that provides support for object-

oriented development. You are not required to use ActionScript to use Flex, but it provides flow

control and object manipulation features that are not available in strict MXML.

Intended audience

This manual assumes that you already installed Macromedia Flex and know how to use it. If you

have written programs before, ActionScript will seem familiar. But if you’re new to programming,

ActionScript isn’t hard to learn. It’s easy to start with simple commands and build more

complexity as you progress.

Using the documentation

This manual provides an overview of ActionScript syntax, information on how to use

ActionScript when working with different types of objects, and details on the syntax and usage of

every language element. The following list summarizes the contents of this manual.

•Chapter 1, “ActionScript Basics,” on page 9 describes the terminology and basic concepts used

in the rest of the manual.

•Chapter 2, “Creating Custom Classes with ActionScript 2.0,” on page 45 describes how to

create custom classes and objects for manipulating data in your applications.

•Chapter 3, “Working with External Data,” on page 67 describes how to process data from

external sources using server- or client-side scripts in your applications.

•Chapter 4, “About the ActionScript Language Reference,” on page 77 provides an overview of

the second part of the manual, which describes the elements that comprise the ActionScript

language.

•Chapter 5, “ActionScript Core Language Elements,” on page 80 explains all of the elements of

the ActionScript language that are not related to a particular class or to a particular

Macromedia product.

•Chapter 6, “ActionScript Core Classes,” on page 232 documents all of the classes of the

ActionScript language that are not related to a particular Macromedia product.

6 Introduction: Getting Started with ActionScript

•Chapter 7, “ActionScript for Flash,” on page 490 describe functions, properties, and classes of

Macromedia Flash Player that you can use in a Macromedia Flex application, if appropriate.

•Appendix A, “Deprecated Flash 4 operators,” on page 809 lists all the ActionScript operators

and their associativity.

•Appendix B, “Keyboard Keys and Key Code Values,” on page 811 lists all the keys on a

standard keyboard and the corresponding ASCII key code values that are used to identify the

keys in ActionScript.

Typographical conventions

The following typographical conventions are used in this manual:

•Code font indicates ActionScript code.

•Code font italic indicates an element, such as an ActionScript parameter or object name,

that you replace with your own text when writing a script.

Terms used in this document

The following terms are used in this manual:

•You refers to the developer who is writing a script or application.

•The user refers to the person who is running your scripts and applications.

•Compile time is the time at which you publish, export, test, or debug your document.

•Runtime is the time at which your script is running in Flash Player.

ActionScript terms such as method and object are defined in Chapter 1, “ActionScript Basics,” on

page 9.

Additional resources

Specific documentation about Macromedia Flash and related products is available separately.

•For information about creating communication applications with Flash Communication

Server, see Developing Communications Applications and Managing Flash Communication Server.

•For information about building Flex applications, see Developing Flex Applications.

The Macromedia DevNet website (www.macromedia.com/devnet) is updated regularly with the

latest information on Flash, plus advice from expert users, advanced topics, examples, tips, and

other updates. Check the website often for the latest news on Flash and how to get the most out

of the program.

The Macromedia Flash Support Center (www.macromedia.com/support/flash) provides

TechNotes, documentation updates, and links to additional resources in the Flash community.

PART I

Welcome to ActionScript

This part includes information on using the ActionScript language. For information on the

classes and language elements you can use in your scripts, see Part II, “Reference.”

Chapter 1: ActionScript Basics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Chapter 2: Creating Custom Classes with ActionScript 2.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Chapter 3: Working with External Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

PART I

CHAPTER 1

ActionScript Basics

ActionScript has rules of grammar and punctuation that determine which characters and words

are used to create meaning and in which order they can be written. For example, in English, a

period ends a sentence; in ActionScript, a semicolon ends a statement.

The general rules described in this section apply to all ActionScript. Most ActionScript terms also

have individual requirements; for the rules for a specific term, see its entry in Part II, “Reference.”

Applying the basics of ActionScript in a way that creates elegant programs can be a challenge for

users who are new to ActionScript.

This section contains the following topics:

•“Differences between ActionScript and JavaScript” on page 10

•“Terminology” on page 11

•“Syntax” on page 13

•“About data types” on page 18

•“Assigning data types to elements” on page 23

•“About variables” on page 27

•“Using operators to manipulate values in expressions” on page 31

•“Using condition statements” on page 39

•“Using built-in functions” on page 41

•“Creating functions” on page 41

10 Chapter 1: ActionScript Basics

Differences between ActionScript and JavaScript

ActionScript is similar to the core JavaScript programming language. You don’t need to know

JavaScript to use and learn ActionScript; however, if you know JavaScript, ActionScript will

seem familiar.

This manual does not attempt to teach general programming. There are many resources that

provide more information about general programming concepts and the JavaScript language.

•The European Computers Manufacturers Association (ECMA) document ECMA-262 is

derived from JavaScript and serves as the international standard for the JavaScript language.

ActionScript is based on the ECMA-262 specification. For more information, see www.ecma-

international.org/publications/standards/Ecma-262.htm.

•Netscape DevEdge Online has a JavaScript Developer Central site (http://

developer.netscape.com/tech/javascript/index.html) that contains documentation and articles

useful for understanding ActionScript. The most valuable resource is the Core JavaScript Guide.

•The Java Technology site has tutorials on object-oriented programming (http://java.sun.com/

docs/books/tutorial/java/index.html) that are targeted for the Java language but are useful for

understanding concepts that you can apply to ActionScript.

Some of the differences between ActionScript and JavaScript are described in the following list:

•ActionScript does not support browser-specific objects such as Document, Window,

and Anchor.

•ActionScript does not completely support all the JavaScript built-in objects.

•ActionScript does not support some JavaScript syntax constructs, such as statement labels.

•In ActionScript, the eval() function can perform only variable references.

•ActionScript2.0 supports several features that are not in the ECMA-262 specification, such as

classes and strong typing. Many of these features are modeled after the ECMAScript 4 Draft

Proposal currently in development by ECMA TC39-TG1 (see www.mozilla.org/js/language/

es4/index.html), the standards committee in charge of the evolution of the ECMA-262

specification.

•ActionScript does not support regular expressions using the RegExp object. However,

Macromedia Central does support the RegExp object.

Unicode support for ActionScript

Macromedia Flex supports Unicode text encoding for ActionScript. This means that you can

include text in different languages in an ActionScript file. For example, you can include text in

English, Japanese, and French in the same file. For more information on Unicode support in Flex,

see “Using MXML” in Developing Flex Applications.

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