ActionScript 3.0 Design Patterns

Minimalist Example of an MVC Pattern | 439

Note the overridden update( ) function in the CompositeView class shown in

Example 12-8. It calls the update method in all its children. Therefore, calling the

update( )function in the root node of the composite view structure will cascade

down and traverse the component tree updating all views. Let’s subclass

CompositeViewandComponentViewclasses and create a nested view structure to see

how this works.

Creating nested views

To illustrate nested views, we will create a composite view node and two child com-

ponent views as shown in Figure 12-2.

We will first create a composite view calledRootNodeView. This composite view will

receive keyboard input events from the stage. This view will also register to receive

aChildren.push(c);
}

override public function update(event:Event = null):void
{
for each (var c:ComponentView in aChildren)
{
c.update(event);
}
}
}
}

Figure 12-2. Nested view structure in minimalist example

Example 12-8. CompositeView.as (continued)

Model

Root node

registers to receive

update notices

RootNodeView

Update events

cascade down from

parent to child views

CharCodeLeafView ACIICharLeafView

Receives update

events from model

Nested views

Displays the

character code of

the key pressed

Displays the ASCII

character code of

the key pressed