加载图片的方法

加载图片时有两种方法，一种是BitmapData直接加入已加载好图片的Loader,另一种是先将UrlLoader的加载模式dataFormat设置为Byte类型URLLoaderDataFormat.BINARY，然后加载好图片后再用Loader的loadBytes(bytes:ByteArray, context:LoaderContext = null):void 加载图片的byte，再将加载byte的Loader加入BitmapData中

用Loader的loadBytes（bytesArray)可以逐渐载入图片

下列代码是逐渐载入图片的示例：

package{
    import flash.display.Sprite;
    import flash.net.URLStream;
    import flash.net.URLRequest;
    import flash.display.Loader;
    import flash.utils.ByteArray;
    import flash.utils.getTimer;
    import flash.events.Event;
    import flash.events.ProgressEvent;
    import flash.display.Bitmap;
    import flash.display.BitmapData;
    import flash.geom.Rectangle;

    import flash.text.TextField;

    public class ImageProLoad extends Sprite{
        //define all the properties
        private var loader:Loader;
        private var imageStream:URLStream;
        private var imageData:ByteArray;

        private var tf:TextField;

        //constructor
        public function ImageProLoad():void{
             tf = new TextField();
             this.addChild(tf);
             tf.width = 500;
             tf.selectable = false;
                   init();
             loadImage("http://www.ezrabessaroth.net/images/oldinterioreb.bmp");
            }

        private function init():void{
            loader = new Loader();
            this.addChild(loader);
            loader.cacheAsBitmap = true;
            imageStream = new URLStream();
            imageStream.addEventListener(ProgressEvent.PROGRESS,imageStreamProgress);
            imageStream.addEventListener(Event.COMPLETE,imageStreamComplete);
            loader.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS,displayImage);
            }

        private function imageStreamProgress(event:ProgressEvent):void{
            //if there are no bytes load, do nothing
            if (imageStream.bytesAvailable == 0) return;
            //process the data
            processImageData();
            }

        private function imageStreamComplete(event:Event):void{
            //check if connection there, stop it
            if (imageStream.connected){
                imageStream.close();
                }
            }

        private function processImageData():void{
            //if connnected, read all the bytes in the byteArray;
            if (imageStream.connected){
                imageStream.readBytes(imageData,imageData.length);
                }
                tf.text = "Bytes Loading: " + imageData.bytesAvailable;
            //clean all the data in the loader
            loader.unload();
            //push the aggregate byteArray data in the loader
            loader.loadBytes(imageData);
            }

        //function to loading the image
        private function loadImage(addr:String):void{
            //check if the connection there, then stop it
            //for a new connection to be step up;
            if (imageStream.connected){
                imageStream.close();
                }
            //load a new image url
            imageStream.load(new URLRequest(addr+'?'+getTimer()));
            //clean the loader
            loader.unload();
            //create a new byteArray to store the aggregate data
            imageData = new ByteArray();
            }

        //function to display the image
        private function displayImage(event:ProgressEvent):void{
            }
        }//end of the class
    }//end of the package