.net获取年初，年末。从一年的第一天输出到年末。从1月1号开始输出到12月31号。从一年的第一天输出到当然日期。输出1到12月。月初时间和月末时间。时间日期相关。某个月最后一天。本周周一与周日。本周，本月，每周，每月

电脑版发表于：2020/11/19 18:29

[TOC]

## 获取年初，年末，从一年的第一天输出到年末
### 方法1
```
DateTime startYear = new DateTime(DateTime.Now.Year, 1, 1);   //本年年初
DateTime endYear = new DateTime(DateTime.Now.Year, 12, 31);   //本年年末

//获取一年的天数
int days = (DateTime.IsLeapYear(DateTime.Now.Year) ? 366 : 365);

//从一年的第一天输出到年末
for (int i = 0; i < days; i++)
{    
    Console.WriteLine(startYear.Date.AddDays(i).ToShortDateString());
}
```
**效果如下**
从1月1号开始
![](https://img.tnblog.net/arcimg/aojiancc2/d06f71edc7ae4f6b8a090a28ef4252eb.png)
输出到12月31号
![](https://img.tnblog.net/arcimg/aojiancc2/b0ba97f610d0408882c76a67b52e3b6b.png)

### 方法2：
```
DateTime startYear = new DateTime(DateTime.Now.Year, 1, 1);   //本年年初
DateTime endYear = new DateTime(DateTime.Now.Year, 12, 31);   //本年年末

//通过日期差来计算天数
double days = (endYear - startYear).TotalDays;
Console.WriteLine(days);

//从一年的第一天输出到年末
for (int i = 0; i <= days; i++)
{    
    Console.WriteLine(startYear.Date.AddDays(i).ToShortDateString());
}
```
## 从一年的第一天输出到当前日期
```
DateTime startYear = new DateTime(DateTime.Now.Year, 1, 1);   //本年年初
//通过日期差来计算天数
double days = (DateTime.Now - startYear).TotalDays;
Console.WriteLine(days);

//从一年的第一天输出到当然日期
for (int i = 0; i <= days; i++)
{    
    Console.WriteLine(startYear.Date.AddDays(i).ToShortDateString());
}
```
## 输出1到12月
```
DateTime startYear = new DateTime(DateTime.Now.Year, 1, 1);   //本年年初

for (int i = 0; i < 12; i++)
{
    Console.WriteLine(startYear.AddMonths(i).ToString("yyyy-MM-dd"));
}
```
![](https://img.tnblog.net/arcimg/aojiancc2/b825e295ecfe4319aa942e40918ffef5.png)


## 根据传过来的月份，计算这个月最后一天
```
/// <summary>
/// 根据传过来的月份，计算这个月最后一天
/// </summary>
/// <param name="month"></param>
/// <returns></returns>
public  DateTime GetMonthEndTime(DateTime month)
{
    //本月第一天时间      
    DateTime stime = month.AddDays(1 - (month.Day));
    //获得某年某月的天数    
    int y = month.Date.Year;
    int m = month.Date.Month;
    int dayCount = DateTime.DaysInMonth(y, m);
    DateTime endtime = stime.AddDays(dayCount - 1);
    return endtime;
}
```

## 输出某月的月初时间和月末时间
**封装一个方法**
```
/// <summary>
/// 根据时间点计算当月开始时间和结束时间
/// </summary>
/// <param name="date"></param>
/// <returns></returns>
public static DateTime[] GetMonthStatTimeAndEndTime(DateTime date)
{
    //你可能需要处理一下时区
    //date = date.ToCstTime();

    //本月第一天时间      
    DateTime stime = date.AddDays(1 - (date.Day));
    //获得某年某月的天数    
    int y = date.Date.Year;
    int m = date.Date.Month;
    int dayCount = DateTime.DaysInMonth(y, m);
    DateTime etime = stime.AddDays(dayCount - 1);

    return new List<DateTime>() { stime, etime }.ToArray();
    //return new List<DateTime>() { DateTime.Parse("2000-1-1"), DateTime.Parse("2022-4-9") }.ToArray();
}
```
调用：
![](https://img.tnblog.net/arcimg/aojiancc2/2d542a6f9e4348328d65914a077afc2d.png)

## 获取从1月至12月的月初时间和月末时间
```
DateTime startYear = new DateTime(DateTime.Now.Year, 1, 1);   //本年年初

for (int i = 0; i < 12; i++)
{
    DateTime[] dateTimes = DateTimeTools.GetMonthStatTimeAndEndTime(startYear.AddMonths(i));
    Console.WriteLine(dateTimes[0].ToString("yyyy-MM-dd") + "--" + dateTimes[1].ToString("yyyy-MM-dd"));
}
```
![](https://img.tnblog.net/arcimg/aojiancc2/898bfd02da574df596d99ebb72ca0f4a.png)


## 获取从1月至当前月的月初时间和月末时间
```
DateTime startYear = new DateTime(DateTime.Now.Year, 1, 1);   //本年年初

//获取当前月
int month = DateTime.Now.Month;

for (int i = 0; i < month; i++)
{
    DateTime[] dateTimes = DateTimeTools.GetMonthStatTimeAndEndTime(startYear.AddMonths(i));
    Console.WriteLine(dateTimes[0].ToString("yyyy-MM-dd") + "--" + dateTimes[1].ToString("yyyy-MM-dd"));
}
```
![](https://img.tnblog.net/arcimg/aojiancc2/97a2f5909ca446c58a2203279fb06b0a.png)

## C#获取本周的周一以及周日
```
/// <summary>
/// C#获取本周的周一以及周日
/// </summary>
/// <returns></returns>
public static DateTime[] GetWeekStartAndEnd()
{
    DateTime dt = DateTime.Now;
    int dayOfWeek = -1 * (int)dt.Date.DayOfWeek;
    //Sunday = 0,Monday = 1,Tuesday = 2,Wednesday = 3,Thursday = 4,Friday = 5,Saturday = 6,

    DateTime weekStartTime = dt.AddDays(dayOfWeek + 1);//取本周一
    if (dayOfWeek == 0) //如果今天是周日，则开始时间是上周一
    {
        weekStartTime = weekStartTime.AddDays(-7);
    }

    return new List<DateTime>() { weekStartTime.Date, weekStartTime.Date.AddDays(6) }.ToArray();
}
```

## 按本日，本周，本月的时间范围查询
```
DateTime beginDate = DateTime.Now.Date;
DateTime endDate = _params.dateTime.Date.AddDays(1);

// 按天统计
if (_params.Type == "dateParamDay")
{
    endDate = beginDate.Date.AddDays(1);
}

// 按周统计
if (_params.Type == "dateParamWeek")
{
    int dayOfWeek = -1 * (int)beginDate.Date.DayOfWeek;

    DateTime weekStartTime = beginDate.AddDays(dayOfWeek + 1);//取本周一
    if (dayOfWeek == 0) //如果今天是周日，则开始时间是上周一
    {
        weekStartTime = weekStartTime.AddDays(-7);
    }

    beginDate = weekStartTime;
    endDate = weekStartTime.Date.AddDays(7);
}

// 按月统计
if (_params.Type == "dateParamMonth")
{
    //本月第一天时间      
    DateTime stime = beginDate.AddDays(1 - (beginDate.Day));
    beginDate = stime;
    endDate = beginDate.AddMonths(1);
}

// 根据选择的时间范围查询
List<StuDailyAssignment> stuDailyAssignments = BaseDal.Db.Queryable<StuDailyAssignment>().Where(a => studentIDList.Contains(a.StuID) && a.DAStatus != 1 && a.CreateTime >= beginDate && a.CreateTime < endDate).ToList();
```

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