C#获取每个年,月,周的起始日期和结束日期的方法

/// <summary>
/// 声明期间类型枚举
/// </summary>
public enum Period {Day, Week, Month, Year};
/// <summary>
/// 获取指定期间的起止日期
/// </summary>
/// <param name="period">期间类型</param>
/// <param name="beginDate">开始日期</param>
/// <param name="endDate">结束日期</param>
public static void GetPeriod(Period period, out DateTime beginDate, out DateTime endDate)
{
  int year = DateTime.Today.Year;
  int month = DateTime.Today.Month;
  switch (period)
  {
    case Period.Year: //年
      beginDate = new DateTime(year, 1, 1);
      endDate = new DateTime(year, 12, 31);
      break;
    case Period.Month: //月
      beginDate = new DateTime(year, month, 1);
      endDate = beginDate.AddMonths(1).AddDays(-1);
      break;
    case Period.Week: //周
      int week = (int)DateTime.Today.DayOfWeek;
      if (week == 0) week = 7; //周日
      beginDate = DateTime.Today.AddDays(-(week - 1));
      endDate = beginDate.AddDays(6);
      break;
    default: //日
      beginDate = DateTime.Today;
      endDate = DateTime.Today;
      break;
  }
}