ActionScript 3.0 Design Patterns

Minimalist Abstract Decorator | 139

Wrapping Up

To execute the Decorator design pattern, the whole key lies in knowing how to wrap

a component in a concrete decorator. First, you need to instantiate a concrete

component.

var testComponent:Component = new ConcreteComponent( );

Then, you wrap the component in one or more decorations using the following

format:

componentInstance=new ConcreteDecorator(testComponent);

So, in our example, with two concrete decorations, we’d write:

testComponent=new DecConA(testComponent);

testComponent=new DecConB(testComponent);

At this point,testComponentis decorated with two decorations. We could duplicate

the above lines adding the same two decorations as often as we wanted. Think of the

decorations as red and green Christmas tree ornaments. The tree could be covered

with nothing but red and green ornaments, rather than just one of each. The Decora-

tor design pattern is employed cumulatively. That is, as you add each decoration, it’s

added to those already wrapping the concrete component.

Finally, to see what havoc we’ve wrought, we use the getter method—

getInformation( ):

trace(testComponent.getInformation( ));

To see how all of this works, save Example 4-6 asDecTest.asin an ActionScript file.

Then open a new Flash document file, and typeDecTestin the Document class win-

dow in the Properties panel.

Example 4-5. DecConB.as

package
{
//Concrete Decorator "Beta"
public class DecConB extends Decorator
{
var components:Component;
public function DecConB(components:Component) {
this.components=components;
}
override public function getInformation( ):String
{
return components.getInformation( ) + " Decoration Beta:";
}
}
}