c# - 如何获得一年中的特定日期？

Question

我想做一个课程调度器。例如，所有星期五的课程都相同，应该在调度程序上显示。我怎样才能得到一年中所有星期五的日期？我有一些数据字段；

-Dayofweek  int
-Starthour  int
-finishhour int

Answer 1

就是这样，注意365可能是366。你可以判断一下。。

 DateTime dt=DateTime.Parse(DateTime.Now.ToString("yyyy-01-01"));
   for (int i = 0; i < 365;i++ )
   {
       if (dt.AddDays(i).DayOfWeek==DayOfWeek.Friday)
       {
           Console.WriteLine(dt.AddDays(i).ToShortDateString());
       }

   }

Answer 2

static IEnumerable<DateTime> GetAllDaysInYearByDayOfWeek(int year, DayOfWeek dayOfWeek)
{
    var startOfYear = new DateTime(year, 1, 1);
    var firstMatchingDate = startOfYear.AddDays((dayOfWeek - startOfYear.DayOfWeek + 7) % 7);
    for (var dt = firstMatchingDate; dt.Year == year; dt = dt.AddDays(7))
        yield return dt;
}

例如：

var fridays = GetAllDaysInYearByDayOfWeek(2013, DayOfWeek.Friday);
foreach (DateTime day in fridays)
    Console.WriteLine(day.ToShortDateString());

结果：

01/04/2013
01/11/2013
01/18/2013
...
12/13/2013
12/20/2013
12/27/2013