C# 日期帮助类【原创】

      因项目需要简单的写了个日期帮助类，备忘一下！

C#-CODE

//============================================================
// Producnt name:  BoBoARTS.CodeMad
// Version:    1.0
// Author:       董广祥
// Auto generated at:  2009-8-7 13:36:20
//============================================================
using System;

/// <summary>
/// 日期帮助类
/// </summary>
public static class Utility
{
    //当天
    public static string NowTime()
    {
        return DateTime.Now.Year.ToString() + "-" + DateTime.Now.Month.ToString() + "-" + DateTime.Now.Day.ToString();
    }

    //当天日期减去相应天数
    public static string GetTimeByDayReduce(double day)
    {
        return DateTime.Now.Year.ToString() + "-" + DateTime.Now.Month.ToString() + "-" + DateTime.Now.AddDays(day).Day.ToString();
    }

    //指定月份年份的第一天
    public static DateTime GetFirstDayOfMonth(int Year, int Month)
    {
        return Convert.ToDateTime(Year.ToString() + "-" + Month.ToString() + "-1");
    }

    //指定月份年份的最后一天
    public static DateTime GetLastDayOfMonth(int Year, int Month)
    {
        int Days = DateTime.DaysInMonth(Year, Month);
        return Convert.ToDateTime(Year.ToString() + "-" + Month.ToString() + "-" + Days.ToString());
    }

    //当前一周时间
    public static void ThisWeek(out string bDate, out string eDate)
    {
        DateTime firstDay = Convert.ToDateTime(NowTime());
        double theday;
        if (firstDay.DayOfWeek == DayOfWeek.Sunday) { theday = 7; }
        else if (firstDay.DayOfWeek == DayOfWeek.Monday) { theday = 1; }
        else if (firstDay.DayOfWeek == DayOfWeek.Tuesday) { theday = 2; }
        else if (firstDay.DayOfWeek == DayOfWeek.Wednesday) { theday = 3; }
        else if (firstDay.DayOfWeek == DayOfWeek.Thursday) { theday = 4; }
        else if (firstDay.DayOfWeek == DayOfWeek.Friday) { theday = 5; }
        else { theday = 6; }
        double bday = -theday;
        double eday = 7 - theday;
        bDate = firstDay.AddDays(bday).ToString();
        eDate = firstDay.AddDays(eday).ToString();
    }

    //过去一周时间
    public static void BeforeWeek(out string bDate, out string eDate)
    {

        DateTime firstDay = Convert.ToDateTime(GetTimeByDayReduce(-ThisWeekLastDay() + 1));
        double theday;
        if (firstDay.DayOfWeek == DayOfWeek.Sunday) { theday = 7; }
        else if (firstDay.DayOfWeek == DayOfWeek.Monday) { theday = 1; }
        else if (firstDay.DayOfWeek == DayOfWeek.Tuesday) { theday = 2; }
        else if (firstDay.DayOfWeek == DayOfWeek.Wednesday) { theday = 3; }
        else if (firstDay.DayOfWeek == DayOfWeek.Thursday) { theday = 4; }
        else if (firstDay.DayOfWeek == DayOfWeek.Friday) { theday = 5; }
        else { theday = 6; }
        double bday = -theday;
        double eday = 7 - theday;
        bDate = firstDay.AddDays(bday).ToString();
        eDate = firstDay.AddDays(eday).ToString();
    }

    //本周最后一天
    public static double ThisWeekLastDay()
    {
        DateTime firstDay = Convert.ToDateTime(NowTime());
        double theday;
        if (firstDay.DayOfWeek == DayOfWeek.Sunday) { theday = 7; }
        else if (firstDay.DayOfWeek == DayOfWeek.Monday) { theday = 1; }
        else if (firstDay.DayOfWeek == DayOfWeek.Tuesday) { theday = 2; }
        else if (firstDay.DayOfWeek == DayOfWeek.Wednesday) { theday = 3; }
        else if (firstDay.DayOfWeek == DayOfWeek.Thursday) { theday = 4; }
        else if (firstDay.DayOfWeek == DayOfWeek.Friday) { theday = 5; }
        else { theday = 6; }
        return 7 - theday;
    }

    //本月第一天
    public static DateTime GetFirstDayOfMonthTime()
    {
        return GetFirstDayOfMonth(DateTime.Now.Year, DateTime.Now.Month);
    }

    //本月最后一天
    public static DateTime GetLastDayOfMonthTime()
    {
        return GetLastDayOfMonth(DateTime.Now.Year, DateTime.Now.Month);
    }

    //上月第一天
    public static DateTime GetFirstDayOfBeforeMonthTime()
    {
        return GetFirstDayOfMonth(DateTime.Now.Year, DateTime.Now.Month - 1);
    }

    //上月最后一天
    public static DateTime GetLastDayOfBeforeMonthTime()
    {
        return GetLastDayOfMonth(DateTime.Now.Year, DateTime.Now.Month - 1);
    }
    //根据下拉框状态获取相应的时间
    public static void GetTime(out string lastDateTime, out string firstDateTime, string state)
    {
        switch (state)
        {
            case "": firstDateTime = ""; lastDateTime = "";
                break;
            case "today": firstDateTime = NowTime(); lastDateTime = "";
                break;
            case "yesterday": firstDateTime = NowTime(); lastDateTime = GetTimeByDayReduce(-1);
                break;
            case "last7days": firstDateTime = NowTime(); lastDateTime = GetTimeByDayReduce(-7);
                break;
            case "thisweek": ThisWeek(out firstDateTime, out lastDateTime);
                break;
            case "lastweek": BeforeWeek(out firstDateTime, out lastDateTime);
                break;
            case "thismonth": firstDateTime = GetFirstDayOfMonthTime().ToString(); lastDateTime = GetLastDayOfMonthTime().ToString();
                break;
            case "lastmonth": firstDateTime = GetFirstDayOfBeforeMonthTime().ToString(); lastDateTime = GetLastDayOfBeforeMonthTime().ToString();
                break;
            default: firstDateTime = ""; lastDateTime = "";
                break;
        }
    }
}