DesignPatterns_Command

最近開始在認真的學習DesignPattern
會有這個需求只是覺得程式碼重複性很高又不好維護
來分享一下Command，命令者模式。
命令的介面Interface是命令模式重要的組成, 他讓不同的類別都實作了同一個介面
而命令的呼叫者也不需要知道該命令是在做什麼, 只需要能呼叫該介面函式
就像打開電燈或關掉電燈, 我們只需要知道開、關的功能就好
過程是怎樣把他關掉, 就不是那麼重要
且命令模式另一個好處就是能undo和redo。
現在客戶的需求如下, 場景上有一個方塊物件
和三個按鈕, 分開按下後讓方塊放大、移動、旋轉。
媽呀, 這還不簡單, 直接修改方塊的屬性不就好了
但現在客戶再要再加上undo和redo的功能, 且之後還可能會新增新的按鈕功能
這時候就可以使用Command來設計。

1.建立介面, 讓所有的命令者都實作該方式。
<br />package milkmidi.designpattern.command {<br /> public interface ICommand {<br /> function execute():void<br /> function undo():void<br /> function redo():void<br /> } <br />}<br />
2.建立放大的命令者
<br />package milkmidi.designpattern.command { <br /> import flash.display.DisplayObject;<br /> public class ScaleCommand implements ICommand { <br /> private var _target:DisplayObject<br /> public function ScaleCommand(pTarget:DisplayObject) { <br /> _target = pTarget;<br /> }<br /> public function execute():void {<br /> _target.scaleX += .2;<br /> _target.scaleY += .2;<br /> }<br /> public function redo():void {<br /> execute();<br /> }<br /> public function undo():void {<br /> _target.scaleX -= .2;<br /> _target.scaleY -= .2;<br /> } <br /> } <br />}<br />
3.建立CommandStack物件, 用來管理所有的Command,是個Singleton
<br />package milkmidi.designpattern.command { <br /> public class CommandStack { <br /> private static var _instance:CommandStack;<br /> private var _commands :Array;<br /> private var _index :uint;<br /> <br /> public function CommandStack(pSingletonEnforcer:SingletonEnforcer) {<br /> _commands = new Array();<br /> _index = 0;<br /> } <br /> public static function getInstance():CommandStack {<br /> if(CommandStack._instance == null) {<br /> CommandStack._instance = new CommandStack(new SingletonEnforcer());<br /> }<br /> return _instance;<br /> } <br /> public function putCommand(command:ICommand):void {<br /> _commands[_index++] = command;<br /> _commands.splice(_index, _commands.length - _index);<br /> } <br /> public function previous():ICommand {<br /> trace("previous " + (_index - 1));<br /> return _commands[--_index];<br /> } <br /> public function next():ICommand {<br /> trace("next " + _index);<br /> return _commands[_index++];<br /> }<br /> public function hasPreviousCommands():Boolean {<br /> return _index > 0;<br /> } <br /> public function hasNextCommands():Boolean {<br /> return _index < _commands.length;<br /> }<br /> <br /> }<br />}<br /><br />class SingletonEnforcer { }<br />
4.測試：
<br />package { <br /> import com.bit101.components.PushButton;<br /> import flash.display.Sprite; <br /> import flash.events.MouseEvent;<br /> import milkmidi.designpattern.command.CommandStack;<br /> import milkmidi.designpattern.command.ICommand;<br /> import milkmidi.designpattern.command.MoveCommand;<br /> import milkmidi.designpattern.command.RotateCommand;<br /> import milkmidi.designpattern.command.ScaleCommand;<br /> [SWF(width = "950", height = "500", frameRate = "41", backgroundColor = "#000000", pageTitle = "milkmidi.com")] <br /> <br /> public class CommandTest extends Sprite { <br /> private var _rotateCommand :ICommand;<br /> private var _moveCommand :ICommand; <br /> private var _scaleCommand :ScaleCommand;<br /> private var _commandStack :CommandStack = CommandStack.getInstance();<br /> <br /> public function CommandTest() { <br /> var _rec:RecMC = new RecMC();<br /> _rec.x = 150;<br /> _rec.y = 150;<br /> this.addChild(_rec);<br /> <br /> _rotateCommand = new RotateCommand(_rec);<br /> _moveCommand = new MoveCommand(_rec);<br /> _scaleCommand = new ScaleCommand(_rec);<br /> var _pushBtn:PushButton<br /> _pushBtn = new PushButton(this, 0, 0 , "RotateCommand", rotateCommandHandler); <br /> _pushBtn = new PushButton(this, 0, 20, "ScaleCommand", scaleCommandHandler);<br /> _pushBtn = new PushButton(this, 0, 40, "MoveCommand", moveCommandHandler);<br /> _pushBtn = new PushButton(this, 0, 60, "redo", redoClickHandler);<br /> _pushBtn = new PushButton(this, 0, 80, "undo", undoClickHandler);<br /> }<br /> <br /> private function scaleCommandHandler(e:MouseEvent):void{<br /> _scaleCommand.execute();<br /> _commandStack.putCommand(_scaleCommand);<br /> }<br /> <br /> private function rotateCommandHandler(e:MouseEvent):void{<br /> _rotateCommand.execute();<br /> _commandStack.putCommand(_rotateCommand);<br /> }<br /> <br /> private function moveCommandHandler(e:MouseEvent):void{<br /> _moveCommand.execute();<br /> _commandStack.putCommand(_moveCommand);<br /> } <br /> <br /> private function undoClickHandler(e:MouseEvent):void{ <br /> if(_commandStack.hasPreviousCommands()) {<br /> var _command:ICommand = _commandStack.previous();<br /> _command.undo(); <br /> }<br /> } <br /> private function redoClickHandler(e:MouseEvent):void{ <br /> if(_commandStack.hasNextCommands()) {<br /> var _command:ICommand = _commandStack.next();<br /> _command.redo();<br /> }<br /> }<br /> } <br />}<br />import flash.display.Sprite;<br />internal class RecMC extends flash.display.Sprite {<br /> public function RecMC():void {<br /> this.graphics.beginFill(0xeeeeee);<br /> this.graphics.drawRect(0, 0, 45, 45);<br /> this.graphics.endFill();<br /> } <br />}<br />
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