使用日期。添加并添加带有您想添加的新时间的New TimeSpan

DateTime dt = DateTime.Now
dt.Date.Add(new TimeSpan(12,15,00))

 Using an extencion to DateTime:  

        public enum eTimeFragment
        {
            hours,
            minutes,
            seconds,
            milliseconds
        }
        public static DateTime ClearTimeFrom(this DateTime dateToClear, eTimeFragment etf)
        {
            DateTime dtRet = dateToClear;
            switch (etf)
            {
                case eTimeFragment.hours:
                    dtRet = dateToClear.Date;
                    break;
                case eTimeFragment.minutes:
                    dtRet = dateToClear.AddMinutes(dateToClear.Minute * -1);
                    dtRet = dtRet.ClearTimeFrom(eTimeFragment.seconds);
                    break;
                case eTimeFragment.seconds:
                    dtRet = dateToClear.AddSeconds(dateToClear.Second * -1);
                    dtRet = dtRet.ClearTimeFrom(eTimeFragment.milliseconds);
                    break;
                case eTimeFragment.milliseconds:
                    dtRet = dateToClear.AddMilliseconds(dateToClear.Millisecond * -1);
                    break;
            }
            return dtRet;

        }

像这样使用:

游戏机。WriteLine (DateTime。Now ClearTimeFrom (eTimeFragment时间)。

这个必须返回: 2016-06-06 00:00:00.000

int year = 2012;
int month = 12;
int day = 24;
int hour = 0;
int min = 0;
int second = 23;
DateTime dt = new DateTime(year, month, day, hour, min, second);

由于DateTime是不可变的，所以当需要更改日期组件时，必须创建一个新实例。不幸的是，没有内置功能来设置DateTime实例的各个组件。

使用以下扩展方法

public static DateTime SetPart(this DateTime dateTime, int? year, int? month, int? day, int? hour, int? minute, int? second)
{
    return new DateTime(
        year ?? dateTime.Year,
        month ?? dateTime.Month,
        day ?? dateTime.Day,
        hour ?? dateTime.Hour,
        minute ?? dateTime.Minute,
        second ?? dateTime.Second
    );
}

public static DateTime SetYear(this DateTime dateTime, int year)
{
    return dateTime.SetPart(year, null, null, null, null, null);
}

public static DateTime SetMonth(this DateTime dateTime, int month)
{
    return dateTime.SetPart(null, month, null, null, null, null);
}

public static DateTime SetDay(this DateTime dateTime, int day)
{
    return dateTime.SetPart(null, null, day, null, null, null);
}

public static DateTime SetHour(this DateTime dateTime, int hour)
{
    return dateTime.SetPart(null, null, null, hour, null, null);
}

public static DateTime SetMinute(this DateTime dateTime, int minute)
{
    return dateTime.SetPart(null, null, null, null, minute, null);
}

public static DateTime SetSecond(this DateTime dateTime, int second)
{
    return dateTime.SetPart(null, null, null, null, null, second);
}

您可以设置单独的DateTime组件，如

var now = DateTime.Now;

now.SetSecond(0);

我刚刚遇到这篇文章，因为我有一个类似的问题，我想在MVC中为一个实体框架对象设置时间，从视图(datepicker)中获取日期，所以时间组件是00:00:00，但我需要它是当前时间。根据这篇文章中的回答，我想出了:

myEntity.FromDate += DateTime.Now.TimeOfDay;

DateTime出了什么问题。AddSeconds方法，您可以添加或减去秒?