Question

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How to implement Undo and Redo feature in as3

I am going to create an application in that i have to implement an Undo and Redo feature.
In the application there will be multiple objects located on stage and user can customize
the position of the objects. But when user clicks on Undo the object go back to their default
position and after clicking on redo object will move on the new position.

So my question is how can i apply these feature in my application?
Is there any library or any third party classes?

Can some one help me?

Thanks in advance.

Answer 1

This seemed like a fun exercise. The following tracks start and end coordinates of display objects, supports undo/redo and destroys redo actions when a new movement is made. It’s probably a bit simple and restrictive for your needs, but could be easily extended by adding to the VO.

HistoryVO:

package  {

    import flash.display.DisplayObject;

    public class HistoryVO {

        public var mc:DisplayObject;
        public var oldX:Number;
        public var oldY:Number;
        public var newX:Number;
        public var newY:Number;

        public function HistoryVO($mc:DisplayObject,$oldX:Number,$oldY:Number)
        {
            mc = $mc;
            oldX = $oldX;
            oldY = $oldY;
        }
    }
}

HistoryManager:

package  {

    import flash.display.DisplayObject;

    public class HistoryManager {

        private var historyList:Vector.<HistoryVO>;

        private var tempVO:HistoryVO;

        private var index:int;

        public function HistoryManager() 
        {
            //initialize the list
            historyList = new Vector.<HistoryVO>();
            index = -1;
        }

        public function createEntry($mc:DisplayObject,$oldX:Number,$oldY:Number):void
        {
            //create a tempory VO to store the old position and the object
            tempVO = new HistoryVO($mc,$oldX,$oldY);
        }

        public function finishEntry($mc:DisplayObject,$newX:Number,$newY:Number):void
        {
            //make sure this is the same object
            if($mc == tempVO.mc) {
                tempVO.newX = $newX;
                tempVO.newY = $newY;
                if(historyList.length > index+1) {
                    //delete any future history
                    historyList = historyList.splice(0,index+1);
                }
                historyList.push(tempVO);
                index++;
            } else {
                throw new Error("Target DisplayObject does not match the stored value");
            }
        }

        //redo
        public function nextStep():void
        {
            if(historyList.length > index+1) {
                var step:HistoryVO = historyList[++index];
                step.mc.x = step.newX;
                step.mc.y = step.newY;
            }
        }

        //undo
        public function previousStep():void
        {
            if(index > -1) {
                var step:HistoryVO = historyList[index--];
                step.mc.x = step.oldX;
                step.mc.y = step.oldY;
            }
        }
    }
}

Example document class:

package  {

    import flash.events.Event;
    import flash.events.MouseEvent;
    import flash.display.Sprite;
    import flash.display.MovieClip;

    public class Main extends MovieClip {

        private var history:HistoryManager;

        private var movies:Vector.<Sprite>;

        private var backBut:Sprite;
        private var nextBut:Sprite;

        public function Main() 
        {
            history = new HistoryManager();
            movies = new Vector.<Sprite>();
            (stage) ? init() : addEventListener(Event.ADDED_TO_STAGE,init);
        }

        private function init(evt:Event = null):void
        {
            //create some sprites to play with
            for(var i:int = 0; i < 5; i++) {
                movies[i] = addChild(new Sprite()) as Sprite;
                movies[i].x = Math.round(Math.random() * 500);
                movies[i].y = Math.round(Math.random() * 350);
                movies[i].graphics.beginFill(Math.round(Math.random()*0xFFFFFF));
                movies[i].graphics.drawRect(0,0,50,50);
                movies[i].graphics.endFill();
                movies[i].addEventListener(MouseEvent.MOUSE_DOWN,onDown);
                movies[i].addEventListener(MouseEvent.MOUSE_UP,onUp);
            }
            //create the buttons
            backBut = addChild(new Sprite()) as Sprite;
            backBut.graphics.beginFill(0x000000);
            backBut.graphics.drawRect(0,0,100,30);
            backBut.addEventListener(MouseEvent.CLICK,previousStep);
            nextBut = addChild(new Sprite()) as Sprite;
            nextBut.x = 110;
            nextBut.graphics.beginFill(0x000000);
            nextBut.graphics.drawRect(0,0,100,30);
            nextBut.addEventListener(MouseEvent.CLICK,nextStep);
        }

        private function onDown(evt:MouseEvent):void
        {
            history.createEntry(Sprite(evt.target),evt.target.x,evt.target.y);
            evt.target.startDrag();
        }

        private function onUp(evt:MouseEvent):void
        {
            evt.target.stopDrag();
            history.finishEntry(Sprite(evt.target),evt.target.x,evt.target.y);
        }

        private function previousStep(evt:MouseEvent):void
        {
            history.previousStep();
        }

        private function nextStep(evt:MouseEvent):void
        {
            history.nextStep();
        }
    }
}