c#DateTime相关运用合集

① 获取当月开始日期和结束日期

DateTime currentTime = DateTime.Now;
DateTime CurrentMonthStart = DateTime.Parse($"{currentTime.Year}-{currentTime.Month+1}-1");//当月开始日期
int days=System.Threading.Thread.CurrentThread.CurrentUICulture.Calendar.GetDaysInMonth(currentTime.Year, currentTime.Month+1);//当月天数

DateTime CurrentMonthEnd = DateTime.Parse($"{currentTime.Year}-{currentTime.Month+1}-{days}");//当月结束日期

②获取本周开始时间和结束时间

DateTime weekstar = DateTime.Parse(DateTime.Now.AddDays(-(int)DateTime.Now.DayOfWeek + 1).ToString("yyyy-MM-dd 00:00:00"));
DateTime weekend = DateTime.Parse(DateTime.Now.AddDays(7 -(int)DateTime.Now.DayOfWeek).ToString("yyyy-MM-dd 23:59:59"));

③ 获取当月第一天和下个月第一天

DateTime DateNow = DateTime.Now;
DateTime DateBegin1 = new DateTime(DateNow.Year, DateNow.Month, 1);//当月第一天
//获取下个月第一天
DateTime DateNow1 = DateNow.AddMonths(1);
DateTime DateBegin2 = new DateTime(DateNow1.Year, DateNow1.Month, 1);//下个月第一天

④ 计算两个日期之间相差的天数

相关参考网址：https://blog.csdn.net/zht666/article/details/21601403

                      https://blog.csdn.net/e_wsq/article/details/7278760

TimeSpan ts1 = new TimeSpan(time1.Ticks);
TimeSpan ts2 = new TimeSpan(time2.Ticks);
TimeSpan ts = time1.Subtract(time2.Now).Duration();
int dateDiff = ts.Days;

⑤今天是星期几

1.string[] Day = new string[] { "星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六" };
string week = Day[Convert.ToInt32(DateTime.Now.DayOfWeek.ToString("d"))].ToString();
lbDay.Text = week; 
2.
public static string dt;
public static string week;
dt = DateTime.Today.DayOfWeek.ToString();
switch (dt)
{
case "Monday":
week = "星期一";
break;
case "Tuesday":
week = "星期二";
break;
case "Wednesday":
week = "星期三";
break;
case "Thursday":
week = "星期四";
break;
case "Friday":
week = "星期五";
break;
case "Saturday":
week = "星期六";
break;
case "Sunday":
week = "星期日";
break;
}
lbDay.Text = week; 
3.string Week =System.Globalization.CultureInfo.CurrentCulture.DateTimeFormat.GetDayName(DateTime.Now.DayOfWeek);

⑥查询某月某周几的日期

  foreach (MaintenanceDutyPsersonDto item in maintenanceDuty)
                {
                    string yearandmonth = item.DutyDate.ToString("yyyy-MM");
                    int year = item.DutyDate.Year;
                    int month = item.DutyDate.Month;
                    int d = DateTime.DaysInMonth(year, month);   //获取指定年月的天数
                    if (item.Dutymodel == "周")//按周排班
                    {
                        string[] weeks = item.weeks;
                        List<string> datelist1 = new List<string>();
                        for (int i = 0; i < weeks.Length; i++)
                        {
                            switch (weeks[i])
                            {
                                case "周一":
                                    for (int a = 1; a <= d; a++)
                                    {
                                        DateTime dt = new DateTime(year, month, a);
                                        if (dt.DayOfWeek == DayOfWeek.Monday)
                                        {
                                         
                                          datelist1.Add(dt.ToShortDateString());
                                          
                                        }
                                    }
                                    break;
                                case "周二":
                                    for (int a = 1; a <= d; a++)
                                    {
                                        DateTime dt = new DateTime(year, month, a);
                                        if (dt.DayOfWeek == DayOfWeek.Tuesday)
                                        {

                                            datelist1.Add(dt.ToShortDateString());

                                        }
                                    }
                                    break;
                                case "周三":
                                    for (int a = 1; a <= d; a++)
                                    {
                                        DateTime dt = new DateTime(year, month, a);
                                        if (dt.DayOfWeek == DayOfWeek.Wednesday)
                                        {

                                            datelist1.Add(dt.ToShortDateString());

                                        }
                                    }
                                    break;
                                case "周四":
                                    for (int a = 1; a <= d; a++)
                                    {
                                        DateTime dt = new DateTime(year, month, a);
                                        if (dt.DayOfWeek == DayOfWeek.Thursday)
                                        {

                                            datelist1.Add(dt.ToShortDateString());

                                        }
                                    }
                                    break;
                                case "周五":
                                    for (int a = 1; a <= d; a++)
                                    {
                                        DateTime dt = new DateTime(year, month, a);
                                        if (dt.DayOfWeek == DayOfWeek.Friday)
                                        {

                                            datelist1.Add(dt.ToShortDateString());

                                        }
                                    }
                                    break;
                                case "周六":
                                    for (int a = 1; a <= d; a++)
                                    {
                                        DateTime dt = new DateTime(year, month, a);
                                        if (dt.DayOfWeek == DayOfWeek.Saturday)
                                        {

                                            datelist1.Add(dt.ToShortDateString());

                                        }
                                    }
                                    break;
                                case "周日":
                                    for (int a = 1; a <= d; a++)
                                    {
                                        DateTime dt = new DateTime(year, month, a);
                                        if (dt.DayOfWeek == DayOfWeek.Sunday)
                                        {

                                            datelist1.Add(dt.ToShortDateString());

                                        }
                                    }
                                    break;
                                default:

                                    break;

                            }
                        }

⑦ 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();
}

⑧判断某个日期是否在某段日期范围内

/// <summary>
/// 获取某段日期范围内的所有日期，以字符串形式返回
/// </summary>
/// <param name="startDate">开始日期</param>
/// <param name="endDate">结束日期</param>
/// <returns></returns>
protected string GetDate(DateTime startDate, DateTime endDate)
{
    string result = string.Empty;
    for (DateTime temp = startDate.ToShortDateString(); temp <= endDate.ToShortDateString(); temp = temp.AddDays(1))
    {
        if (result == string.Empty)
        {
            result = temp.ToString();
        }
        else
        {
            result += "," + temp.ToString();
        }
    }
    return result;
}

⑨  C#时间类型 DateTime? 赋空值 关于datetime类型的DBNull判断

public DateTime? SubTime { get; set; }
  //日期类型判断是否为null 用nullable这个泛型结构体
  m.SubTime=dr["subtime"]==DBNull.Value?new Nullable<DateTime>():Convert.ToDateTime(dr["subtime"])

⑩合集

/今天  
DateTime.Now.Date.ToShortDateString();  
//昨天，就是今天的日期减一  
DateTime.Now.AddDays(-1).ToShortDateString();  
//明天，同理，加一  
DateTime.Now.AddDays(1).ToShortDateString();  
   
//本周(要知道本周的第一天就得先知道今天是星期几，从而得知本周的第一天就是几天前的那一天，要注意的是这里的每一周是从周日始至周六止  
DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();  
DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();  
//如果你还不明白，再看一下中文显示星期几的方法就应该懂了  
//由于DayOfWeek返回的是数字的星期几，我们要把它转换成汉字方便我们阅读，有些人可能会用switch来一个一个地对照，其实不用那么麻烦的                
string[] Day = new string[] { "星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六" };  
Day[Convert.ToInt16(DateTime.Now.DayOfWeek)];  
   
//上周，同理，一个周是7天，上周就是本周再减去7天，下周也是一样  
DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek))) - 7).ToShortDateString();  
DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek))) - 7).ToShortDateString();  
//下周  
DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek))) + 7).ToShortDateString();  
DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek))) + 7).ToShortDateString();  
//本月,很多人都会说本月的第一天嘛肯定是1号，最后一天就是下个月一号再减一天。当然这是对的  
//一般的写法  
DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() + "1"; //第一天  
DateTime.Parse(DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() + "1").AddMonths(1).AddDays(-1).ToShortDateString();//最后一天  
   
//巧用C#里ToString的字符格式化更简便  
DateTime.Now.ToString("yyyy-MM-01");  
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(1).AddDays(-1).ToShortDateString();  
   
//上个月，减去一个月份  
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(-1).ToShortDateString();  
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();  
//下个月，加去一个月份  
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(1).ToShortDateString();  
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(2).AddDays(-1).ToShortDateString();  
//7天后  
DateTime.Now.Date.ToShortDateString();  
DateTime.Now.AddDays(7).ToShortDateString();  
//7天前  
DateTime.Now.AddDays(-7).ToShortDateString();  
DateTime.Now.Date.ToShortDateString();  
   
//本年度，用ToString的字符格式化我们也很容易地算出本年度的第一天和最后一天  
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).ToShortDateString();  
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(1).AddDays(-1).ToShortDateString();  
//上年度，不用再解释了吧  
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(-1).ToShortDateString();  
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddDays(-1).ToShortDateString();  
//下年度  
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(1).ToShortDateString();  
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(2).AddDays(-1).ToShortDateString();  
   
//本季度，很多人都会觉得这里难点，需要写个长长的过程来判断。其实不用的，我们都知道一年四个季度，一个季度三个月  
//首先我们先把日期推到本季度第一个月，然后这个月的第一天就是本季度的第一天了  
DateTime.Now.AddMonths(0 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01");  
//同理，本季度的最后一天就是下季度的第一天减一  
DateTime.Parse(DateTime.Now.AddMonths(3 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();  
//下季度
DateTime.Now.AddMonths(3 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01");  
DateTime.Parse(DateTime.Now.AddMonths(6 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();  
//上季度  
DateTime.Now.AddMonths(-3 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01");  
DateTime.Parse(DateTime.Now.AddMonths(0 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();