ActionScript for Flash MX: The Definitive Guide, Second Edition

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

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Chapter 14: Movie Clip Subclasses and Components

Creating the Library Symbol

Before returning to the code in Example 14-1, let’s set up our movie’s assets. Each

movie clip subclass is associated with a movie clip symbol stored in the Library. To

create instances of the subclass programmatically, we must export the symbol for use

with ActionScript. Here are the steps we follow to create and export a movie clip

symbol for our Ball class:

1. Create a movie clip symbol, named ballSymbol, that contains a circle shape.

2. In the Library, select ballSymbol.

3. From the Library’s pop-up Options menu, select Linkage. The Linkage Proper-

ties dialog box appears.

4. Select the Export For ActionScript checkbox.

5. In the Identifier field, type

ballSymbol.

6. Click OK.

Next, we’ll create the Ball constructor function that will be invoked automatically

every time an instance of ballSymbol is created.

main( );

// Function: main( )

// Desc: Application entry point

function main ( ) {

// Create an object whose properties will be used

// as the Ball constructor's parameters

var ballParams = new Object( );

ballParams.radius = 10;

ballParams.ballColor = 0xFF0000;

ballParams.x = 250;

ballParams.y = 250;

ballParams.velocity = {x:12, y:4};

// Assign the ballParams object to a single property

// of initObj ...