/// <summary>
  /// 生成页码的html
  /// </summary>
  /// <param name="urlFormat">超链接的格式。list.ashx?pagenum={pageNum}。地址中用{pagenum}做为当前页码的占位符</param></param>
  /// <param name="totalSize">总数据条数</param>
  /// <param name="pageSize">每页多少条数据</param>
  /// <param name="currentPage">当前页</param>
  /// <returns></returns>
  public static RawString Pager(string urlFormat, long totalSize,
   long pageSize, long currentPage)
  {
   StringBuilder sb = new StringBuilder();
   //总页数
   long totalPageCount = (long)Math.Ceiling((totalSize * 1.0f) / (pageSize * 1.0f));
   //当前页的前几页
   long firstPage = Math.Max(currentPage - 5, 1);
   //当前页的后几页
   long lastPage = Math.Min(currentPage + 6, totalPageCount);
   //绘制分页,首页
   sb.AppendLine("<div><a href='" + urlFormat.Replace("{pageNum}", "1") + "'>首页</a>");
   //绘制分页中间数据部分
   for (long i = firstPage; i < lastPage; i++)
   {
    string url = urlFormat.Replace("{pageNum}", i.ToString());
    if (i == currentPage) //点击后就不显示超链接
    {
     sb.AppendLine("<a>" + i + "</a>");
    }
    else
    {
     sb.AppendLine("<a href='" + url + "'>" + i + "</a>");
    }
   }
   //显示最后一页
   sb.AppendLine("<a href='" + urlFormat.Replace("{pageNum}", totalPageCount.ToString()) + "'>末页</a></div>");
   return new RawString(sb.ToString());
  }