ActionScript: The Definitive Guide

Movie Clip Methods

In Chapter 12, we learned about a special type of property called a method, which is a function attached to an object. Methods are most commonly used to manipulate, interact with, or control the objects to which they are attached. To control movie clips in various programmatic ways, we may use one of the built-in movie clip methods. We may also define our own movie clip methods in an individual instance or in the Library symbol of a movie clip.

Creating Movie Clip Methods

To add a new method to a movie clip, we define a function on the clip’s timeline (or in one of the clip’s event handlers) or we assign a function to a property of the clip. For example:

// Create a method by defining a function on the timeline of a clip
function halfSpin( ) {
  _rotation += 180;
}
// Create a method by assigning a function literal to a property of a clip
myClip.coords = function( ) { return [_x, _ y]; };
// This method applies a custom transformation to a clip
myClip.myTransform = function ( ) {
  _rotation += 10;
  _xscale -= 25;
  _ yscale -= 25;
  _alpha -= 25;
}

Invoking Movie Clip Methods

Invoking a method on a movie clip works exactly like invoking a method on any object. We supply the name of the clip and the name of the method, as follows:

                  myClip.methodName( );

If the method requires arguments, we pass them along during invocation:

_root.square(5);   // Provide 5 as an argument to the square() method

As we learned earlier, when we’re working on the timeline of a clip or in a clip’s event ...