list<DateTime> 排序
list<DateTime>  li.OrderByDescending(a => a.Year).ToList();

li我想先按年倒序派，如果年相同再按月升序派，该怎么写？  都是一个字段

                magaView.HasMonth = db.Library.Where(a => a.CategoryID == categoryId).GroupBy(a => a.TimeBook.Year * 12 + a.TimeBook.Month - 1).Select(a => a.Key).ToList().     //找寻有杂志的月份

                    Select(a => new DateTime((int)Math.Floor(a / 12.0), a % 12 + 1, 1)).OrderByDescending(a => a.Year).ToList();

------解决方案--------------------
.OrderByDescending(a => a.Year).ThenByDescending(a=>a.Month).ToList();
------解决方案--------------------
 var query = li.OrderByDescending(a => a.Year).ThenBy(a => a.Month).ToList();

List<DateTime> li = new List<DateTime>() { DateTime.Now, DateTime.Now.AddMonths(1), DateTime.Now.AddMonths(1), DateTime.Now.AddMonths(2), DateTime.Now.AddMonths(2), DateTime.Now.AddYears(1), DateTime.Now.AddYears(1).AddMonths(2), DateTime.Now.AddYears(2).AddMonths(1), DateTime.Now.AddYears(2) };

            li.ForEach(x => Console.WriteLine(x));

            Console.WriteLine("--------------------------------");

            var query = li.OrderByDescending(a => a.Year).ThenBy(a => a.Month).ToList();

            query.ForEach(x => Console.WriteLine(x));

------解决方案--------------------

 List<DateTime> list = new List<DateTime>

            {

                DateTime.Now.AddYears(1),

                DateTime.Now.AddYears(1).AddMonths(1),

                DateTime.Now.AddYears(1).AddMonths(2),

                DateTime.Now.AddYears(1).AddMonths(3),

                DateTime.Now.AddYears(1).AddMonths(4),

                DateTime.Now.AddYears(1).AddMonths(5),

                DateTime.Now.AddYears(1).AddMonths(6),

                DateTime.Now.AddYears(2),

                DateTime.Now.AddYears(2).AddMonths(1),

                DateTime.Now.AddYears(2).AddMonths(1)