User Guide

326 Appendix E: Object-Oriented Programming with ActionScript 1
To assign a method to a custom object:
1. Define the constructor function Circle():
function Circle(radius) {
this.radius = radius;
}
2. Define the getArea() method of the Circle object. The getArea() method calculates the area
of the circle. In the following example, you can use a function literal to define the
getArea()
method and assign the
getArea property to the circle’s prototype object:
Circle.prototype.getArea = function () {
return Math.PI * this.radius * this.radius;
};
3. The following example creates an instance of the Circle object:
var myCircle = new Circle(4);
4. Call the getArea() method of the new myCircle object using the following code:
var myCircleArea = myCircle.getArea();
trace(myCircleArea); //traces 50.265...
ActionScript searches the myCircle object for the getArea() method. Because the object
doesn’t have an
getArea() method, its prototype object Circle.prototype is searched for
getArea(). ActionScript finds it, calls it, and traces myCircleArea.
Defining event handler methods in ActionScript 1
You can create an ActionScript class for movie clips and define the event handler methods in the
prototype object of that new class. Defining the methods in the prototype object makes all the
instances of this symbol respond the same way to these events.
You can also add an
onClipEvent() or on() event handler action to an individual instance to
provide unique instructions that run only when that instance’s event occurs. The
onClipEvent()
and
on() actions don’t override the event handler method; both events cause their scripts to run.
However, if you define the event handler methods in the prototype object and also define
an event handler method for a specific instance, the instance definition overrides the
prototype definition.
To define an event handler method in an object’s prototype object:
1. Create a movie clip symbol and set the linkage ID to theID by selecting the symbol in the
Library panel and selecting Linkage from the Library options menu.
2. In the Actions panel (Window > Development Panels > Actions), use the function action to
define a new class, as shown in the following example:
// define a class
function myClipClass() {}