得到一周的周一和周日的日期

第一种方法
#region 得到一周的周一和周日的日期

    /// <summary>
    /// 计算本周的周一日期
    /// </summary>
    /// <returns></returns>
    public static DateTime GetMondayDate()
    {
        return GetMondayDate(DateTime.Now);
    }

    /// <summary>
    /// 计算本周周日的日期
    /// </summary>
    /// <returns></returns>
    public static DateTime GetSundayDate()
    {
        return GetSundayDate(DateTime.Now);
    }

    ///   <summary>   
    ///   计算某日起始日期（礼拜一的日期）   
    ///   </summary>   
    ///   <param name="someDate">该周中任意一天</param>   
    ///   <returns>返回礼拜一日期，后面的具体时、分、秒和传入值相等</returns>   
    public static DateTime GetMondayDate(DateTime someDate)
    {
        int i = someDate.DayOfWeek - DayOfWeek.Monday;
        if (i == -1) i = 6;//   i值   >   =   0   ，因为枚举原因，Sunday排在最前，此时Sunday-Monday=-1，必须+7=6。   
        TimeSpan ts = new TimeSpan(i, 0, 0, 0);
        return someDate.Subtract(ts);
    }

    ///   <summary>   
    ///   计算某日结束日期（礼拜日的日期）   
    ///   </summary>   
    ///   <param name="someDate">该周中任意一天</param>   
    ///   <returns>返回礼拜日日期，后面的具体时、分、秒和传入值相等</returns>   
    public static DateTime GetSundayDate(DateTime someDate)
    {
        int i = someDate.DayOfWeek - DayOfWeek.Sunday;
        if (i != 0) i = 7 - i;//   因为枚举原因，Sunday排在最前，相减间隔要被7减。   
        TimeSpan ts = new TimeSpan(i, 0, 0, 0);
        return someDate.Add(ts);
    }

    #endregion


第二种方法
System.DateTime dtNow = System.DateTime.Now;
        System.TimeSpan tsMon = new TimeSpan((int)(dtNow.DayOfWeek - System.DayOfWeek.Monday), 0, 0, 0);
        System.TimeSpan tsFri = new TimeSpan((int)(System.DayOfWeek.Friday - dtNow.DayOfWeek), 0, 0, 0);

        Response.Write("Monday   is   " + (dtNow - tsMon).ToString() + "</br>");
        Response.Write("friday   is   " + dtNow.ToString() + "</br>");
        Response.Write("Today   is   " + (dtNow + tsFri).ToString() + "</br>");


第三种方法
        int t = (int)DateTime.Now.DayOfWeek;
        DateTime moday = DateTime.Now.AddDays(1 - t);
        DateTime friday = DateTime.Now.AddDays(5 - t);
        DateTime now = DateTime.Now;
        Response.Write("Moday" + moday + "</br>");
        Response.Write("friday" + friday + "</br>");