datetime各种处理。记录下，备不时之需。

1. 获取某段日期范围内的所有日期

/// <summary>
    /// 获取某段日期范围内的所有日期，以数组形式返回
    /// </summary>
    /// <param name="dt1">开始日期</param>
    /// <param name="dt2">结束日期</param>
    /// <returns></returns>
    private DateTime[] GetAllDays(DateTime dt1, DateTime dt2)
    {
        List<DateTime> listDays = new List<DateTime>();
        DateTime dtDay = new DateTime();
        for (dtDay = dt1; dtDay.CompareTo(dt2) <= 0; dtDay = dtDay.AddDays(1))
        {
            listDays.Add(dtDay);
        }
        return listDays.ToArray();
    }

2. 根据年份和周次获得对应的时间范围

/// <summary>
    /// 根据年份和周次获得对应的时间范围
    /// </summary>
    /// <param name="yearInt"></param>
    /// <param name="weekInt"></param>
    /// <returns></returns>
    private string range(int yearInt, int weekInt)
    {
        int year, year1, year2, month1, month2, day1, day2, week, sum = 0;
        int[] days = new int[] { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
        int i;
        year = yearInt;
        week = weekInt;
        sum += 7 * (week - 1);        //修正总天数   
        switch (DateTime.Parse(year + "-1-1").DayOfWeek)
        {
            case DayOfWeek.Tuesday: { sum -= 1; break; }
            case DayOfWeek.Wednesday: { sum -= 2; break; }
            case DayOfWeek.Thursday: { sum -= 3; break; }
            case DayOfWeek.Friday: { sum -= 4; break; }
            case DayOfWeek.Saturday: { sum -= 5; break; }
            case DayOfWeek.Sunday: { sum -= 6; break; }
            default:
                break;
        }
        if ((year % 400 == 0) || (year % 4 == 0 && year % 100 != 0))
        { days[1] = 29; } for (i = 0; i < days.Length; i++)
        {
            if (sum >= days[i]) { sum -= days[i]; } else { break; }
        } year1 = year; month1 = i + 1; day1 = sum + 1;//修改开始日期   
        if (day1 < 1)
        { day1 += days[11]; month1 = 12; year1--; }
        year2 = year1; month2 = month1; day2 = day1 + 6;
        if (day2 > days[month1 - 1])
        {
            day2 -= days[month1 - 1];
            month2++; if (month2 > 12) { month2 = 1; year2++; }
        }
        string ss = year1 + "年" + month1 + "月" + day1 + "日~" + year2 + "年" + month2 + "月" + day2 + "日";
    
        return ss;
    }

3. 根据系统当前时间获得今天是今年的第几周

/// <summary>
    /// 根据系统当前时间获得今天是今年的第几周
    /// </summary>
    /// <param name="date"></param>
    /// <returns></returns>
    private int WeekOfYear(string date)
    {
        DateTime curDay = Convert.ToDateTime(date);

        int firstdayofweek = Convert.ToInt32(Convert.ToDateTime(curDay.Year.ToString() + "- " + "1-1 ").DayOfWeek);

        int days = curDay.DayOfYear;
        int daysOutOneWeek = days - (7 - firstdayofweek);

        if (daysOutOneWeek <= 0)
        {
            return 1;
        }
        else
        {
            int weeks = daysOutOneWeek / 7;
            if (daysOutOneWeek % 7 != 0)
                weeks++;

            return weeks + 1;
        }
    }

4.datetime.now.tostring("dddd");获得当前日期的星期几。