Programming Flash Communication Server

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Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 4: Applications, Instances, and Server-Side ActionScript

// The user variable holds an instance of the User class

user = new User( );

In Flash 5 and Flash MX, this would essentially disable the constructor, but in SSAS,

the difference in capitalization means that User (the class) and

user (a variable hold-

ing an instance of the class) are different entities. A common practice to avoid confu-

sion is to append the word “Class” onto the constructor function name:

function UserClass ( ) {

}

user = new UserClass( );

Working with Inheritance

Server-Side ActionScript does not support the formal definition of classes and inter-

faces supported by client-side ActionScript 2.0. SSAS supports prototype-based

inheritance but is a little different from Flash ActionScript 1.0. Flash MX added the

super operator to client-side ActionScript to make it easy to call the constructor func-

tion and methods of a superclass. Although super is not part of the ECMAScript ver-

sion 3 language defined in ECMA-262, it is proposed for a future version of the

standard. The super operator is not available in SSAS. However you can permit a

subclass to access the constructor and methods of a superclass in a number of ways

in SSAS. Example 4-1 shows one way to call the constructor and methods of a super-

class in SSAS.

Example 4-1. Calling the constructor and methods of a superclass in SSAS

SuperClass = function (a) {

this.a = a;

};

SuperClass.prototype.method = function ( ) {

trace("SuperClass method called. a is: " + this.a);

};

SubClass = function (a, b) {

SuperClass.apply(this, arguments);

this.b = b;

};

SubClass.prototype = new SuperClass( );

SubClass.constructor = SubClass;

SubClass.prototype.method = function ( ) {

trace("In Subclass method. a and b: " + this.a + ", " + this.b);

SuperClass.prototype.method.apply(this, arguments);

};

subClass = new SubClass(1, 2);

subClass.method( );