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Flash MX Programmer's Guide to ActionScript 2.0

The more tools you have, the more you can build

Flash developers who are still using ActionScript 1.0 are drastically limiting their capabilities, wasting valuable time and resources. Because most Flash developers come from a nonprogramming background, they don't fully understand the true power and benefits of ActionScript 2.0. This article attempts to clear up some common misconceptions about AS2 and gives some clear examples demonstrating the new concepts and methodologies that can be applied using it.

AS1 Is Not Deprecated
What is now referred to as AS1 is the same AS you'll find in Flash MX. Contrary to popular belief, the AS1 programming style - using prototype objects as classes - is not deprecated. You can still write prototype objects and modify existing objects' prototypes in AS2 using the exact same AS1 syntax. AS2 does not deprecate AS1; it extends and refines it.

Class Declarations
With AS1 you could only use prototype objects to define a class (see Code I).

For component development you would also have to use the #initclip and #endinitclip pragmas as well as the Object.registerClass method to assign your class to a MovieClip in the library.

With AS2 you could still write the same prototype object or you could write a true class. To write a class you need to define your class in a separate AS file much as you would in Flash MX for external AS. For classes, the AS file must have the same name as the class itself. Some people might find this to be a hindrance; however, this requirement actually helps you better organize and structure your code (see Code II).

The prototype object and the class example do the exact same thing. For comparison, the constructor function was left in the example in Code II. However, a class does not explicitly have to have a constructor function defined as it does for prototype objects. In addition, no other code is required for component development. You can simply specify which class a MovieClip should use in the MovieClip's Linkage Properties panel found in the library.

When compared side-by-side you can see that the class definition is actually cleaner looking and is less redundant. In the prototype example, for every method of a class you must type the name of the object you're adding the method to and the location of the method (specified by prototype).

Some might argue that despite the redundancy the prototype approach is actually more flexible because you can add a method to any class dynamically at anytime in AS1. (This is known as delegation.) Again, AS2 doesn't deprecate AS1, so you can still reference an object's prototype even inside a class definition (see Code III).

Properties
In AS1 you could add a property to a prototype object by first declaring a method to be used as a getter and then declaring another method to be used as a setter. Then you had to use an addProperty method on the prototype object to wire the getter and setter methods together as one property (see Code IV).

You can still use the exact same syntax in AS2 or you can just declare a getter and setter function (see Code V).

In the example in Code V, Flash MX 2004 Pro does all the work of the addProperty method for you and automatically ties the getter and setter methods together in a property named "_prop". Note that this is no longer needed in most cases, saving you some extra typing.

Static, Public, Private
In AS1 there was no supported way of specifying a public, private, or static method. However, with AS2 this is possible (see Code VI).

A public method simply means that an outside object is allowed to directly access the specified property or method. A private method or property may only be accessed internally from within the class. Static methods or properties are similar to private methods in that they may only be called from within the class itself. However, static methods or properties are created only once per class rather than being created in every object based on that class.

Strict Data Typing
Another new feature of AS2 is Strict Data Typing (aka Type Casting). This allows you to cast (assign) a specific data type or class to a variable. It is especially useful when debugging. Say, for example, in AS1 you have a prototype object called List that has a method called "addNewValue":

var MyList = new List();
MyList.addNewVlaue(1);

However, when you test the movie the value never gets added to the List and you are forced to figure out the problem on your own. Granted, a typo like this by itself is pretty easy to find. However, buried in a couple thousand lines of code it may not be as obvouis.

Strict Data Typing deals with this problem by allowing only public methods or properties of nondynamic classes to be called (see Code VII).

Case Sensitivity and Member Variables
Another new addition to AS2 is case sensitivity. This means that a variable called "someVar" would have a different memory location than "somevar" would. This allows each variable to exist without one overwriting the other. In addition, gone are the days of declaring an instance/member variable anywhere inside of a prototype object as in Code VIII.

In AS2 classes you have to declare all your member variables first (see Code IX). Some developers find this to be an inconvenience initially (especially when converting old AS1 code to AS2). However, over time this will help make you a more consistent programmer and will make your code easier to read and maintain. Note the use of m_ in front of someVar. This is just a naming convention I've adapted in my source code to specify a private member variable.

Conclusion
With all the features of AS1 and the many new additions to AS2, most of which I didn't even get a chance to cover in this article, Flash developers refusing to use AS2 are limiting the tools and capabilities they have for completing a job. You wouldn't want to build a house with just a hammer. A good developer knows, just like any construction worker, that the more tools you have in your tool box, the more things you can potentially build.

More Stories By Erik Bianchi

Erik Bianchi, a member of the editorial board of Web Designer's & Developer's Journal, is a software engineer with more than five years of experience developing Flash-based RIAs and enterprise-wide applications for Fortune 50 and 500 companies. In his spare time he enjoys building Flash-based games, writing or tech editing Flash-related books, and when burned out on code, playing video games on his PC/console systems. You can get more info about Erik and his latest projects on his blog at www.erikbianchi.com.

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Most Recent Comments
Erik Bianchi 03/17/04 03:28:43 PM EST

Obvious was intentionally misspelled to demonstrate how easy it is to overlook a typo. Many people didn't notice despite the bolding. Probably should have put a note in there or something to clarify. =)

Thanks for your post and sorry for the confusion.

-erik

A. MacDonald 03/17/04 10:14:49 AM EST

spelling mistake in news - it was pretty OBVIOUS

var MyList = new List();
MyList.addNewVlaue(1);

However, when you test the movie the value never gets added to the List and you are forced to figure out the problem on your own. Granted, a typo like this by itself is pretty easy to find. However, buried in a couple thousand lines of code it may not be as >>> obvouis. << ERROR <<

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