C#获取时间段：今天，昨天，本周，上周，本月，上月，本季度，上季度，今年，去年

参考：https://www.iteye.com/blog/xqf222-1920357

https://blog.csdn.net/u011981242/article/details/51595546

    /// <summary>
    /// 获取时间段（某段时间的0时0分0秒-23时59分59秒）
    /// </summary>
    public class DateTimeHelper
    {
        /// <summary>
        /// 当前时间
        /// </summary>
      //public  static DateTime dt = DateTime.Now; //当前时间  

        //DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") //24小时制 
        //DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss")  //12小时制  

        /// <summary>
        /// 今天开始,0时0分0秒：
        /// </summary>
        public static DateTime startCurrentDay= Convert.ToDateTime(DateTime.Now.ToString("D").ToString());

        /// <summary>
        /// 今天结束,23时59分59秒：
        /// </summary>
        //public static DateTime endCurrentDay = Convert.ToDateTime(DateTime.Now.AddDays(1).ToString("D").ToString()).AddSeconds(-1);
        //public static DateTime endCurrentDay = DateTime.Now.Date.AddDays(1).AddSeconds(-1);
        public static DateTime endCurrentDay = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day, 23, 59, 59);

        /// <summary>
        /// 昨天开始
        /// </summary>
        public static DateTime startLastDay = DateTime.Now.AddDays(-1).Date;

        /// <summary>
        /// 昨天结束
        /// </summary>
        public static DateTime endLastDay = startLastDay.AddDays(1).AddSeconds(-1);


        /// <summary>
        /// 今天星期几
        /// </summary>
        public static int currentDayOfWeek = Convert.ToInt32(DateTime.Now.DayOfWeek.ToString("d")); 

        /// <summary>
        /// 本周周一
        /// </summary>
        public static DateTime startCurrentWeek = DateTime.Now.AddDays(1 - ((currentDayOfWeek == 0) ? 7 : currentDayOfWeek)).Date;  

        /// <summary>
        /// 本周周日
        /// </summary>
        public static DateTime endCurrentWeek = startCurrentWeek.AddDays(7).AddSeconds(-1);   

        /// <summary>
        /// 上周周一
        /// </summary>
        public static DateTime startLastWeek = startCurrentWeek.AddDays(-7).Date;  

        /// <summary>
        /// 上周周日
        /// </summary>
        public static DateTime endLastWeek = startLastWeek.AddDays(7).AddSeconds(-1); 

        /// <summary>
        /// 本月月初
        /// </summary>
        public static DateTime startCurrentMonth = DateTime.Now.AddDays(1 - DateTime.Now.Day).Date; //本月月初  

        /// <summary>
        /// 本月月末
        /// </summary>
        public static DateTime endCurrentMonth = DateTime.Now.AddDays(1 - DateTime.Now.Day).Date.AddMonths(1).AddSeconds(-1); //本月月末  //DateTime endMonth = startMonth.AddDays((dt.AddMonths(1) - dt).Days - 1);  //本月月末    

        /// <summary>
        /// 上月月初
        /// </summary>
        public static DateTime startLastMonth = DateTime.Now.AddMonths(-1).Date.AddDays(1 - DateTime.Now.Day);

        /// <summary>
        /// 上月月末
        /// </summary>
        public static DateTime endLastMonth = DateTime.Parse(DateTime.Now.AddDays(1 - DateTime.Now.Day).ToShortDateString()).AddSeconds(-1);

        /// <summary>
        /// 本季度初
        /// </summary>
        public static DateTime startCurrentQuarter = DateTime.Now.AddMonths(0 - (DateTime.Now.Month - 1) % 3).AddDays(1 - DateTime.Now.Day).Date; //本季度初  

        /// <summary>
        /// 本季度末
        /// </summary>
        public static DateTime endCurrentQuarter = startCurrentQuarter.AddMonths(3).AddSeconds(-1); //本季度末   

        /// <summary>
        /// 上季度初
        /// </summary>
        public static DateTime startLastQuarter = startCurrentQuarter.AddMonths(-3).Date;

        /// <summary>
        /// 上季度末
        /// </summary>
        public static DateTime endLastQuarter = startLastQuarter.AddMonths(3).AddSeconds(-1);   

        /// <summary>
        /// 今年年初
        /// </summary>
        public static DateTime startCurrentYear = new DateTime(DateTime.Now.Year, 1, 1).Date; //本年年初 

        /// <summary>
        /// 今年年末
        /// </summary>
        public static DateTime endCurrentYear = new DateTime(DateTime.Now.Year, 12,31, 23, 59, 59); //本年年末

        /// <summary>
        /// 去年年初
        /// </summary>
        public static DateTime startLastYear = startCurrentYear.AddYears(-1).Date; 

        /// <summary>
        /// 去年年末
        /// </summary>
        public static DateTime endLastYear = endCurrentYear.AddYears(-1); 

        //至于昨天、明天、上周、上月、上季度、上年度等等，只要AddDays()、AddMonths()、AddYears()这几种方法组合一下就可以了。

    }