适用于多种查询结果集的分页（不要存储过程，简单易懂）

//==================这是用的API====================
        //分页查询
        [Route("api/page")]
        [HttpGet]
        public PageModel GetPage(int pagesize = 3, int pageindex = 1, string coupontype = "", string couponname = "", int state = 2)
        {
            if (pageindex < 1)//正确传入页码
            {
                pageindex = 1;
            }
            //查询出所有数据
            List<GetrecordModel> list = getbll.GetGetrecords();
            //判断该集合是否为空
            if (list != null && list.Count > 0)
            {
                //根据条件进行判断
                if (!string.IsNullOrEmpty(coupontype))
                {
                    list = list.Where(s => s.CouponType == coupontype).ToList();
                }
                if (!string.IsNullOrEmpty(couponname))
                {
                    list = list.Where(s => s.CouponName == couponname).ToList();
                }
                if (state == 1 || state == 0)
                {
                    list = list.Where(s => s.State == state).ToList();
                }
            }
            int count = list.Count;//获取查询后的总条数
            int page;//用来存储页数变量
            //计算页数
            if (count % pagesize == 0)
            {
                page = count / pagesize;
            }
            else
            {
                page = count / pagesize + 1;
            }
            if (pageindex > page)//正确传入页码
            {
                pageindex = page;
            }
            //分页显示
            list = list.Skip((pageindex - 1) * pagesize).Take(pagesize).ToList();

            //定义一个PageModel存储分页后的数据以及页码、页数、总页数
            var m = new PageModel();
            m.list = list;
            m.PageIndex = pageindex;
            m.TotalCount = count;
            m.TotalPage = page;
            return m;
        }