ActionScript 3.0 Design Patterns.pdf - VideoTutorials-bg.com

Executing the following statements accesses the third child of the second child of the
root node; which is leaf 5. The parent of leaf 5 is the second child of the root node
(see Figure 6-4).
var leaf5:Component = root.getChild(2).getChild(3);
var leaf5Parent:Composite = l5.getParent( );
Calling the operation( ) on the parent of leaf 5 should give the following output.
composite 2
leaf 3
leaf 4
leaf 5
Implementing the remove method
The primary concern with removing nodes has to do with removing all references to
deleted objects so that the garbage collector can recover the memory they used. For
example, before removing a composite node, all its child nodes need to be deleted. If
one of the child nodes is itself a composite, then the remove method should recursively
delete its children as well. Therefore, the remove method will work similar to
the operation( ) method.
From the previous scenario, it is evident that we need to treat leaf nodes and composite
nodes differently when deleting them. Therefore, it’s useful to declare a
getComposite( ) method in the Component class to return the composite object if it is
indeed a composite, and null if not. The default behavior would be to return null.
The following method would be defined with its default implementation in the
Component class.
internal function getComposite( ):Composite
{
return null;
}
The Composite class would override this method and return the actual composite
object.
override internal function getComposite( ):Composite
{
return this;
}
In addition, the parent references of components should be removed before components
can be removed. The following method to remove the parent reference should
be defined and implemented in the Component class.
internal function removeParentRef( ):void
{
this.parentNode = null;
}
Minimalist Example of a Composite Pattern | 213