从线程中的URL下载Android

Question

我使用以下代码从URL下载文件：

Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
                URL url = new URL(address);
                Log.i("URL:",address);
                URLConnection connection = url.openConnection();
                connection.setReadTimeout(timeout);
                connection.setConnectTimeout(sockettimeout);
                int filesize = connection.getContentLength();
                InputStream inputStream = connection.getInputStream();
                OutputStream outputStream =new FileOutputStream(path);
                byte[] buffer = new byte[2*1024];
                int length = 0 ;
                downloadedSize = 0;
                while((length = inputStream.read(buffer))>0){

                    outputStream.write(buffer,0,length);
                    downloadedSize += length;
                    Log.i("downloaded Size",""+downloadedSize);

                    listener.onDownloadPercentListener((downloadedSize*100)/filesize);

                    if(downlaodedSize == filesize){
                        listener.onDownloadCompleteListener();
                    }   
                } 
           }
    });
     thread.start();

虽然我的文件已完全下载，但downloadedSize 字段的值始终为零，并且无法执行监听器。
另一个问题是为什么我不能将downloadedSize变量用作本地变量，并且它在 while循环中没有可见性？