air文件的流的读写

<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
<mx:Script>
 <![CDATA[
  import flash.filesystem.*;
  import mx.controls.Alert;
  private function openFile():void
  {
    var txtFilter:FileFilter = new FileFilter("文本文件","*.txt");
    var jpgFilter:FileFilter=new FileFilter("图片文件","*.jpg");//可以打开的文件类型 用来过滤文件的
   var f:File=new File();
   f.browseForOpen("打开",[txtFilter,jpgFilter]);
   f.addEventListener(Event.SELECT,selectHandler);
  }
  private function selectHandler(e:Event):void
  {
   var file:File=e.target as File;
   txt.text=file.nativePath;
   var stream:FileStream = new FileStream();
   stream.open(file,FileMode.READ);
   txtContent.text=stream.readUTFBytes(stream.bytesAvailable);
   stream.close();
  }
  private function modifyText():void
  {
   var file:File=new File(txt.text);//获得文件
   var stream:FileStream=new FileStream();
   stream.open(file,FileMode.WRITE);
   stream.writeUTFBytes(txtContent.text);
   Alert.show("修改成功！");
   stream.close();
  }
 ]]>
</mx:Script>
 <mx:Panel x="138" y="19" width="472" height="315" layout="absolute">
  <mx:Label x="50" y="27" text="文件路径" width="58"/>
  <mx:TextInput x="105" y="25" id="txt"/>
  <mx:Button x="273" y="25" label="浏览" click="openFile()"/>
  <mx:TextArea x="50" y="53" width="306" height="140" id="txtContent"/>
  <mx:Button x="273" y="216" label="修改" click="modifyText()"/>
 </mx:Panel>
 
</mx:WindowedApplication>