Android : android Custom layout Listview with progressbar for music download

i want to develop one music app that connect to server(include music name , singer name, image ,download URL , preview URL) and show in listview and perform user request for downloading music i provide some code and app connect to server and fetch data to

public class MusicDownloadStructure { volatile public String DownloadStatus; volatile public int Progress; volatile public int Size; volatile String Song_Name; volatile String image_id; volatile String sing_type; volatile String singer_name; volatile private ProgressBar ProgressBarRefrence; volatile private TextView ProgressTextviewRefrence;}

`public class Tab2OnlineStoreViewAdapter extends ArrayAdapter { private final Context context; private Download downloadmanager; Fonts font; MusicDownloadStructure[] ModelDownloadData;

private static class ViewHolder {
    public Button Downloadbtn;
    public ProgressBar DownloadProgressbar;
    public TextView DownloadProgress;
    public MusicDownloadStructure data;
}

public Tab2OnlineStoreViewAdapter(Context context2,
        MusicDownloadStructure[] modelDownloadData2) {
    // TODO Auto-generated constructor stub
    super(context2, R.id.listview_tab2, modelDownloadData2);
    context = context2;
    mplayerforprev = new MediaPlayer();
    font = new Fonts(this.context);
    tempfolderpath = MainActivity.fileManger.getTempFolderPath();
    ModelDownloadData = modelDownloadData2;
}

@Override
public View getView(int position, View view, ViewGroup parent) {
    // TODO Auto-generated method stub
    ViewHolder viewHolder = null;
    View convertView = view;
    // service
    final MusicDownloadStructure data = getItem(position);
    if (convertView == null) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.tab2_online_store_row_item,
                null, false);
        viewHolder = new ViewHolder();
        viewHolder.Downloadbtn = (Button) convertView
                .findViewById(R.id.tab2_btn_download);
        viewHolder.DownloadProgressbar = (ProgressBar) convertView
                .findViewById(R.id.tab2_downloadProgressbar);
        viewHolder.DownloadProgress = (TextView) convertView
                .findViewById(R.id.tab2_downloadProgressText);

        viewHolder.data = data;
        convertView.setTag(viewHolder);

    } else {
        viewHolder = (ViewHolder) convertView.getTag();
        viewHolder.data.setProgressBarRefrence(null);
        viewHolder.data.setProgressTextviewRefrence(null);
        viewHolder.data = data;
    }
    data.setProgressBarRefrence(viewHolder.DownloadProgressbar);
    data.setProgressTextviewRefrence(viewHolder.DownloadProgress);
    viewHolder.DownloadProgress.setText(data.getDownloadStatus());
    viewHolder.Downloadbtn.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            downloadmanager = new Download();
            downloadmanager.Downloadmusic(
                    data,
                    "http://www.englishathome.ir/public/karaoke/"
                            + data.getImage_id() + ".zip", context,
                    data.getImage_id(), data.getSong_Name());
        }
    });
    return convertView;
}<br/>