listview 优化

 ViewHolder holder;
      if (convertView == null) {
          final LayoutInflater inflater = (LayoutInflater) mContext
                  .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
          convertView = inflater.inflate(R.layout.list_item_icon_text, null);
          holder = new ViewHolder();
         holder.icon = (ImageView) convertView.findViewById(R.id.icon);
        holder.text = (TextView) convertView.findViewById(R.id.text);
           convertView.setTag(holder);
    } else {
          holder = (ViewHolder) convertView.getTag();
      }
      holder.icon.setImageResource(R.drawable.icon);
   holder.text.setText(mData[position]);
      return convertView;
  }
   static class ViewHolder {
      ImageView icon;
     TextView text;