ActionScript 3.0 Design Patterns

Minimalist Example of an MVC Pattern | 441

Both component view classes CharCodeLeafView (Example 12-10) and

AsciiCharLeafView(Example 12-11) subclass theComponentViewclass (Example 12-8).

Note that they don’t receive any input from the user interface. These two views can

therefore be instantiated without passing a controller object to the constructor. The

controller will default tonull in this case.

Now all that’s left to do is build the MVC triad with the nested view. We’ll allow the

client to build the nested view and register the root node with the model to receive

update events.

Building the Nested View Structure

Building nested view structures is identical to developing composite structures using

the composite pattern. We have to visualize the view as a tree (an upside-down tree)

and use theadd( ) method in the composite view to add child views.

var model:IModel = new Model( );

var controller:IKeyboardInputHandler = new Controller(model);

override public function update(event:Event = null):void
{
// get data from model and update view
trace(model.getKey( ));
}
}
}

Example 12-11. AsciiCharLeafView.as

package
{
import flash.events.Event;

public class AsciiCharLeafView extends ComponentView
{
public function AsciiCharLeafView(aModel:IModel,aController:Object = null)
{
super(aModel, aController);
}

override public function update(event:Event = null):void
{
// get data from model and update view
trace(String.fromCharCode(model.getKey( )));
}
}
}

Example 12-10. CharCodeLeafView.as (continued)