C#获取某年某个星期的第一天和最后一天的日期

/// <summary>
/// 获取某年第几周的第一天和最后一天的日期
/// </summary>
/// <param name="year">年份</param>
/// <param name="weekNumber">第几周</param>
/// <returns></returns>
public Tuple<DateTime, DateTime> GetFirstEndDayOfWeek(int year, int weekNumber)
{
System.Globalization.Calendar calendar = System.Globalization.CultureInfo.CurrentCulture.Calendar;
DateTime firstOfYear = new DateTime(year, 1, 1, calendar);//获取这一年的第一天日期
DateTime targetDay = calendar.AddWeeks(firstOfYear, weekNumber - 1);//加上weekNumber - 1 周的日期
DayOfWeek firstDayOfWeek = System.Globalization.CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek;//星期一：Monday
//获取第weekNumber周第一天的日期
while (targetDay.DayOfWeek != firstDayOfWeek)
{
targetDay = targetDay.AddDays(-1);
}
return Tuple.Create<DateTime, DateTime>(targetDay, targetDay.AddDays(6));
}

/// <summary>
        /// 计算时间差
        /// </summary>
        /// <param name="dateBegin">开始时间</param>
        /// <param name="dateEnd">结束时间</param>
        /// <returns>返回(天)单位，比如: 1天</returns>
        private int ExecDateDiff(DateTime dateBegin, DateTime dateEnd)
        {
            TimeSpan ts1 = new TimeSpan(dateBegin.Ticks);
            TimeSpan ts2 = new TimeSpan(dateEnd.Ticks);
            TimeSpan ts3 = ts1.Subtract(ts2).Duration();
            //你想转的格式
            return ts3.Days;
        }