分页方法,始终只生成指定数量的页码

 /// <summary>
        /// 计算按当前页码及最大生成页条数在总页数时生成的两个下标值
        /// 例如pageIndex=4,当前数据一共有7页(pageLength)
        /// 而需要生成5页(pageCount),那么最终会生成两个值2和6
        /// 前端在使用时只用以2开始以6结尾生成对应的页码标签即可
        /// </summary>
        /// <param name="pageIndex">当前页码</param>
        /// <param name="pageLength">所有页码数量</param>
        /// <param name="pageCount">要生成的页码数量</param>
        /// <returns>第一页的页码,最后一页的页码</returns>
        private Tuple<int, int> GetPages(int pageIndex, int pageLength, int pageCount = 5)
        {
            if (pageIndex > pageLength)
            {
                pageIndex = pageLength;
            }
            if (pageIndex < 1)
            {
                pageIndex = 1;
            }
            if (pageLength <= pageCount)
            {
                return new Tuple<int, int>(1, pageLength);
            }
            else
            {
                int left = 1;
                int count = pageCount;

                if (pageIndex - 2 <= 1)
                {
                    return new Tuple<int, int>(left, count);
                }
                else
                {

                    //left count均要计算
                    if (pageIndex + 2 <= pageLength)
                    {
                        //左右都充足
                        left = pageIndex - 2;
                        count = pageIndex + 2;
                        return new Tuple<int, int>(left, count);
                    }
                    else
                    {
                        //左充右缺
                        count = pageLength;
                        left = pageLength - 4;
                        return new Tuple<int, int>(left, count);

                    }
                }

            }
        }