我们在计算时期的时候，可能会经常需要得到指定日期所在周的第一天与最后一天的日期，又因为我们的计算周的方式与西方有所不同，他们是以星期天为每周的第一天，而我们习惯以星期一为每周的第一天。这里我们分别给出两种不同计算方法的示例，方法如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace WyfClass
{
public class tools
{
/// <summary>
/// 得到本周第一天(以星期天为第一天)
/// </summary>
/// <param name="datetime"></param>
/// <returns></returns>
public DateTime GetWeekFirstDaySun(DateTime datetime)
{
//星期天为第一天
int weeknow = Convert.ToInt32(datetime.DayOfWeek);
int daydiff = (-1) * weeknow;
//本周第一天
string FirstDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
return Convert.ToDateTime(FirstDay);
}
/// <summary>
/// 得到本周第一天(以星期一为第一天)
/// </summary>
/// <param name="datetime"></param>
/// <returns></returns>
public DateTime GetWeekFirstDayMon(DateTime datetime)
{
//星期一为第一天
int weeknow = Convert.ToInt32(datetime.DayOfWeek);
//因为是以星期一为第一天，所以要判断weeknow等于0时，要向前推6天。
weeknow = (weeknow == 0 ? (7 - 1) : (weeknow - 1));
int daydiff = (-1) * weeknow;
//本周第一天
string FirstDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
return Convert.ToDateTime(FirstDay);
}
/// <summary>
/// 得到本周最后一天(以星期六为最后一天)
/// </summary>
/// <param name="datetime"></param>
/// <returns></returns>
public DateTime GetWeekLastDaySat(DateTime datetime)
{
//星期六为最后一天
int weeknow = Convert.ToInt32(datetime.DayOfWeek);
int daydiff = (7 - weeknow) - 1;
//本周最后一天
string LastDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
return Convert.ToDateTime(LastDay);
}
/// <summary>
/// 得到本周最后一天(以星期天为最后一天)
/// </summary>
/// <param name="datetime"></param>
/// <returns></returns>
public DateTime GetWeekLastDaySun(DateTime datetime)
{
//星期天为最后一天
int weeknow = Convert.ToInt32(datetime.DayOfWeek);
weeknow = (weeknow == 0 ? 7 : weeknow);
int daydiff = (7 - weeknow);
//本周最后一天
string LastDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
return Convert.ToDateTime(LastDay);
}
}
}