ActionScript 3 tutorials: Difference between revisions
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Two main aspects of the language: | Two main aspects of the language: | ||
* AS3 is a strongly typed language. This means that whenever you use a variable, you must provide information about the type of data that this variable is expected to hold. If you want to use a counter and keep track of the counter progress in a variable, the type of data to be held in this variable will be of integer type (non negative numbers). To define that counter variable in AS3, you will type something like | |||
var counter:int = 0; | var counter:int = 0; | ||
* AS3 is an object oriented language. This means that you have the possibility to split your code into specialized classes rather than write a single program of 3,000 lines of code. This contributes to make the code easier to maintain and easier to re-use. You can then design specialized components that will be re-used across different applications. A typical example of such a component would be a calendar object that pops up to let you specify a date. | |||
The problem then, for a total newbie, is that the use of classes is not optional. *Everything* needs to be organized into classes. You must have at least one class in your program. This can appear quite obscure at first. But because the class definition always uses the same format, that's simply a question of getting used to add these extra lines in your code. Initially you will write short programs that don't justify the use of more than a single class. Don't worry if you don't understand that class concept yet. What matters is that you start going, start writing a bit of code and become able to play around. We will come back on the concept of class soon enough. | |||
// The class definition | // The class definition | ||
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// code to execute when updateScore () is invoked | // code to execute when updateScore () is invoked | ||
} | } | ||
With the structure in class comes another concept, the one of package. A package is a conceptual container. It is used to group classes that operate together within a physical region of their own. Its main function is to help organize the code for large applications. Another complex concept to grasp for a total beginner. The recommendation here is the same as for classes. In a first time, simply use the syntax without worrying too much about what it is for. Your are likely to write programs that stand within a single package for a few weeks, so don't worry about not understanding it. We will take the time to explain this in more details, as soon as you are up to it. | |||
== EcmaScript Specification == | == EcmaScript Specification == | ||
Revision as of 14:57, 30 October 2007
This pages is for actionscript concepts that apply to any ActionScript 3.0 authoring environment and any runtime that supports ActionScript 3.0. For the moment, two authoring environment are covered in this wiki, Adobe Flash CS3 and Adobe Flex. The focus is on programming concepts rather than tool-specific topics.
Disclaimer
We write these pages as (recent) learners of the language. We are not expert.
Overview
ActionScript 3.0 is an object-oriented language for creating applications and media-content that can then be played back in Flash client runtimes (typically the Adobe Flash Player, more recently the AIR framework).
For those used already familiar with a Flash authoring environment, it needs to be mentioned that quite important changes have been introduced in the ActionScript language between version 2 and version 3. Version 2 was somehow a scripting language targeted at unexperienced programmers. Version 3 has all characteristics of any core programming language used by experienced programmer.
This may make it slightly more difficult for complete beginners to jump in. These changes, however, don't prevent a person who would have never programmed before to learn the language. This is in part because the authoring environment let you define content and basic actions without having to care about code. Progressive learning can take place. The benefits of the changes introduced in version 3 far outweight any possible cost.
Two main aspects of the language:
- AS3 is a strongly typed language. This means that whenever you use a variable, you must provide information about the type of data that this variable is expected to hold. If you want to use a counter and keep track of the counter progress in a variable, the type of data to be held in this variable will be of integer type (non negative numbers). To define that counter variable in AS3, you will type something like
var counter:int = 0;
- AS3 is an object oriented language. This means that you have the possibility to split your code into specialized classes rather than write a single program of 3,000 lines of code. This contributes to make the code easier to maintain and easier to re-use. You can then design specialized components that will be re-used across different applications. A typical example of such a component would be a calendar object that pops up to let you specify a date.
The problem then, for a total newbie, is that the use of classes is not optional. *Everything* needs to be organized into classes. You must have at least one class in your program. This can appear quite obscure at first. But because the class definition always uses the same format, that's simply a question of getting used to add these extra lines in your code. Initially you will write short programs that don't justify the use of more than a single class. Don't worry if you don't understand that class concept yet. What matters is that you start going, start writing a bit of code and become able to play around. We will come back on the concept of class soon enough.
// The class definition
public class Game {
// instance variable of type integer
var score:int
// The constructor method
public function Game () {
// code that initialize Game instances
}
// instance method
public function updateScore ():void {
// code to execute when updateScore () is invoked
}
With the structure in class comes another concept, the one of package. A package is a conceptual container. It is used to group classes that operate together within a physical region of their own. Its main function is to help organize the code for large applications. Another complex concept to grasp for a total beginner. The recommendation here is the same as for classes. In a first time, simply use the syntax without worrying too much about what it is for. Your are likely to write programs that stand within a single package for a few weeks, so don't worry about not understanding it. We will take the time to explain this in more details, as soon as you are up to it.
EcmaScript Specification
ActionScript 3.0 is based on the EcmaScript 4th edition language specification. This specification can be viewed on the wiki of the Ecmascript Organisation. That specification also forms the chore of the Javascript 2.0 language contributed by the Mozilla foundation (see tamarin project at Mozilla.org).