问ActionScript3 -删除位图和bitmapData

EN

var _myThumb:Bitmap;
var _myThumbData:BitmapData;
var bitmap:Bitmap
//
function createThumbs()
        {
_myThumbData = new BitmapData(pic.picdefault.width,pic.picdefault.height,false,0xffffff);
// 
       picthumbs.t1.holder.addChild(createBitmap(_myThumbData));
picthumbs.t2.holder.addChild(createBitmap(_myThumbData));
picthumbs.t3.holder.addChild(createBitmap(_myThumbData));
picthumbs.t4.holder.addChild(createBitmap(_myThumbData));
picthumbs.t5.holder.addChild(createBitmap(_myThumbData));
        }


        function createBitmap(bmd:BitmapData):Bitmap
        {
            var bitmap:Bitmap = new Bitmap(bmd);
                        bitmap.smoothing = true;
            setSize(bitmap, bmd.width, bmd.height, 94, 94);

            return bitmap;
        }


        function setSize(target:DisplayObject, contentWidth:Number, contentHeight:Number, targetWidth:Number, targetHeight:Number):void {
            var w:Number = targetWidth;
            var h:Number = targetHeight;
            var containerRatio:Number = targetWidth / targetHeight;
            var imageRatio:Number = contentWidth / contentHeight;
            if (containerRatio < imageRatio) h = w / imageRatio;
            else                             w = h * imageRatio;
            target.width = w;
            target.height = h;

            target.x = (targetWidth - w) * .5;
            target.y = (targetHeight -h) * .5;

        }
        //

        function createThumbnail()
{
    _myThumbData.draw(pic.picdefault);
}