Android - 通过更新进度栏下载文件

我的 Dropbox 帐户中有多个文件。我成功下载文件。但我想显示带有百分比的进度条，以便在下载所有文件时。进度条完成。我正在使用 AsyncTask 下载文件。这是我的代码。

public void onPreExecute(){

        mDialog = new ProgressDialog(mContext);
        mDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        mDialog.setMax(100);
        mDialog.show();
    }

    public void downloadFiles(String filename){
        Log.i("Item Name",filename);
        File dir = null;
        Boolean isSDPresent = android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED);


        if(isSDPresent){

        File sdCard = Environment.getExternalStorageDirectory();
         dir = new File (sdCard.getAbsolutePath() + "/AllSecure");
        if (!dir.exists()) {
            dir.mkdirs();
        }
        }else{

            dir = mContext.getDir("users", Context.MODE_PRIVATE); //Creating an internal dir;
            if(!dir.exists())
            {
                 dir.mkdirs();
            }     

        }

        File file = new File(dir, filename);
        try {
            FileOutputStream mFileOutputStream=new FileOutputStream(file);

            DropboxFileInfo mDropboxFileInxfo=mApi.getFile(PHOTO_DIR + filename, null, mFileOutputStream, null);

            } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            } catch (DropboxException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            }
    }


    protected String doInBackground(String... params) {

         SessionUtil ses = new SessionUtil(mContext);
            AndroidAuthSession session = ses.buildSession();
            mApi = new DropboxAPI<AndroidAuthSession>(session);


        Entry entries = null;

        try {
            System.out.println("mApi is " + mApi);
            entries = mApi.metadata(PHOTO_DIR, 10000, null, true, null);
        } catch (DropboxException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

        for (Entry e : entries.contents) {
            if (!e.isDeleted) {
                //Log.i("Is Folder",String.valueOf(e.isDir));
                downloadFiles(e.fileName());
                 mFileLen = entries.bytes;
                Log.i("Item Name",e.fileName());
            }
        }



       return null;
    }

    protected void onProgressUpdate(Integer... progress) {

    }

    @Override
    protected void onPostExecute(String result) {
        mDialog.dismiss();



    }

Dropbox API 中有一个有用的抽象类，称为 ProgressListener，我这样使用它

DBApi.getFile(dropPath, null, outputStream, new ProgressListener(){
                    @Override
                    public long progressInterval() {
                        return 500;
                    }
                    @Override
                    public void onProgress(long arg0, long arg1) {
                        int totalSize=(int) arg1;
                        int downloadedSize=(int) arg0;
                        //Here you can interact with progressbar
                    }
                });