How to Create a Flash MX Component - Page 15

Setting Up Inheritance for Components

Now that you can sub-class movie clips easily with Components and tie them to user-defined classes, you can create hierarchies of animations that share foundational elements.

The essential idea is that you make your foundational class inherit from MovieClip, as we have done with triangles, and then sub-classes inherit from the foundational class (or other sub-classes). Because you must define the foundational class first, you must use an order number in the foundational class definition:

#initclip 0

In your sub-classes, you use order numbers greater than the order number of parent classes, such as #initclip 1. This ensures that the foundational element class is defined before the sub-class. To establish the inheritance, in place of inheriting from MovieClip, you would use a statement such as

MySubClass.prototype = new FoundationClass();

Now your sub-class (MySubClass) will have all the properties and methods of the foundation (FoundationClass).

Macromedia's Flash User Interface Components, which include elements such as a list box, a combo box, a push button, and several more, are great examples of using component hierarchies. Each element has unique properties and methods to implement particular behavior, but they all share fundamental style properties and methods such as enabled/disabled states, sizing, and fonts. Designers can modify the global style sheet (GlobalStyleFormat) and all the components that draw from global elements will change. You can create your own composite component by inheriting from any of these classes, too.

When you create the movie clip for the sub-class, you can either place the parent component within the clip or bring the parent component in programmatically via attachMovie or duplicateMovieClip.