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

Example 7-20. CommandWithUndo.as (continued)
}
{
}
internal static var aCommandHistory:Array = new Array( );
public function execute( ):void
{
aCommandHistory.push(this);
}
// ABSTRACT Method (must be overridden in a subclass)
public function undo( ):void {}
Concrete Commands that Implement Undo
Now we will re-implement the increment and decrement concrete commands to the
abstract interface declared by CommandWithUndo. The two new concrete command
classes are IncrementCommandWithUndo (Example 7-21) and DecrementCommandWithUndo
(Example 7-22). To implement the undo feature, we primarily need to push all executed
command objects into the command stack. The execute( ) method does this
by calling the execute( ) method in the superclass in the last statement (line 17), and
implementing the undo( ) method. The undo( ) method simply reverses the effects of
the execute( ) method (line 20).
Example 7-21. IncrementCommandWithUndo.as
1 package
2 {
3 import flash.text.TextField;
4
5 class IncrementCommandWithUndo extends CommandWithUndo
6 {
7 var receiver:TextField;
8
9 public function IncrementCommandWithUndo(rec:TextField):void
10 {
11 this.receiver = rec;
12 }
13
14 override public function execute( ):void
15 {
16 receiver.text = String(Number(receiver.text) + 1);
17 super.execute( );
18 }
19
20 override public function undo( ):void
21 {
Extended Example: Implementing Undo | 267