194 | Chapter 5: Adapter Pattern
interceptkey downevents, we need to attach listeners to interceptmouse downand
mouse moveevents. Note that the listeners should be attached to the stage rather
than theLegacyCarobject. This enables the listener functions to receive mouse clicks
over the broad area of the stage, as opposed to directly over the car object.
this.stage.addEventListener(MouseEvent.MOUSE_MOVE, this.doMouseMove);
this.stage.addEventListener(MouseEvent.MOUSE_DOWN, this.doMouseDown);All that’s required now is to implement the listener functions that call the appropri-
ate methods in the adapter. ThedoMouseDown( )function listens tomouse downevents
and calls thegoStraight( ) method in the adapter.
private function doMouseDown(event:MouseEvent):void
{
this.carAdapter.goStraight( );
}ThedoMouseMove( )function listens tomouse moveevents. It checks whether the
mouse has moved to the left or right from its last position. The last mouse position is
saved in theoldMouseStageXproperty. Based on whether the mouse moved to the left
or right, the adapter methodsturnMoreToTheLeft( )andturnMoreToTheRight( )are
called.
private function doMouseMove(event:MouseEvent):void
{
// change in horizontal mouse position
var xDiff = event.stageX - this.oldMouseStageX;
if (xDiff > 0) {
this.carAdapter.turnMoreToTheRight( );
} else {
this.carAdapter.turnMoreToTheLeft( );
}
event.updateAfterEvent( ); // process this event first
this.oldMouseStageX = event.stageX // save old mouse x position
}As is evident from this example, that well-thought-out design of adapters can be used
in multiple contexts.
Example: List Display Adapter
Adapter patterns also come in handy to create reusable classes that use existing
classes to implement some of the required functionality. For example, think about
when you would want to display a list of values on theStage. There may be many
instances when you want to do this: lists of names, lists of high scores in a game, lists
of products in a shopping cart, etc. In Flash you can use aTextFieldto display a list,
putting each item on a separate line. However, this requires that the display text be
preformatted with a carriage return character ('\r', ASCII 13) separating each list
item before sending it out to theTextFieldobject for display. The following code
snippet will display a list using aTextField object.