How to change time in DateTime?

问题:

How can I change only the time in my DateTime variable "s"?

DateTime s = some datetime;

回答1:

You can't change a DateTime value - it's immutable. However, you can change the variable to have a new value. The easiest way of doing that to change just the time is to create a TimeSpan with the relevant time, and use the DateTime.Date property:

DateTime s = ...;
TimeSpan ts = new TimeSpan(10, 30, 0);
s = s.Date + ts;

s will now be the same date, but at 10.30am.

Note that DateTime disregards daylight saving time transitions, representing "naive" Gregorian time in both directions (see Remarks section in the DateTime docs). The only exceptions are .Now and .Today: they retrieve current system time which reflects these events as they occur.

This is the kind of thing which motivated me to start the Noda Time project, which is now production-ready. Its ZonedDateTime type is made "aware" by linking it to a tz database entry.

回答2:

Alright I'm diving in with my suggestion, an extension method:

public static DateTime ChangeTime(this DateTime dateTime, int hours, int minutes, int seconds, int milliseconds)
{
    return new DateTime(
        dateTime.Year,
        dateTime.Month,
        dateTime.Day,
        hours,
        minutes,
        seconds,
        milliseconds,
        dateTime.Kind);
}

Then call:

DateTime myDate = DateTime.Now.ChangeTime(10,10,10,0);

It's important to note that this extension returns a new date object, so you can't do this:

DateTime myDate = DateTime.Now;
myDate.ChangeTime(10,10,10,0);

But you can do this:

DateTime myDate = DateTime.Now;
myDate = myDate.ChangeTime(10,10,10,0);

回答3:

s = s.Date.AddHours(x).AddMinutes(y).AddSeconds(z);

In this way you preserve your date, while inserting a new hours, minutes and seconds part to your liking.

回答4:

one liner

var date = DateTime.Now.Date.Add(new TimeSpan(4, 30, 0));

would bring back todays date with a time of 4:30:00, replace DateTime.Now with any date object

回答5:

DateTime is an immutable type, so you can't change it.

However, you can create a new DateTime instance based on your previous instance. In your case, it sounds like you need the Date property, and you can then add a TimeSpan that represents the time of day.

Something like this:

var newDt = s.Date + TimeSpan.FromHours(2);

回答6:

If you already have the time stored in another DateTime object you can use the Add method.

DateTime dateToUse = DateTime.Now();
DateTime timeToUse = new DateTime(2012, 2, 4, 10, 15, 30); //10:15:30 AM

DateTime dateWithRightTime = dateToUse.Date.Add(timeToUse.TimeOfDay);

The TimeOfDay property is a TimeSpan object and can be passed to the Add method. And since we use the Date property of the dateToUse variable we get just the date and add the time span.

回答7:

Simplest solution :

DateTime s = //some Datetime that you want to change time for 8:36:44 ;
s = new DateTime(s.Year, s.Month, s.Day, 8, 36, 44);

And if you need a specific Date and Time Format :

s = new DateTime(s.Year, s.Month, s.Day, 8, 36, 44).ToString("yyyy-MM-dd h:mm:ss");

回答8:

Happened upon this post as I was looking for the same functionality this could possibly do what the guy wanted. Take the original date and replace the time part

DateTime dayOpen = DateTime.Parse(processDay.ToShortDateString() + " 05:00 AM");

回答9:

DateTime ts = DateTime.Now;
ts = new DateTime ( ts.Year, ts.Month, ts.Day, 0, 0, 0 ) ;
Console.WriteLine ( "Today = " + ts.ToString("M/dd/yy HH:mm:ss") ) ;

Executed: Today = 9/04/15 00:00:00

回答10:

If you have a DateTime like 2014/02/05 18:19:51 and want just 2014/02/05, you can do that:

_yourDateTime = new DateTime(_yourDateTime.Year, _yourDateTime.Month, _yourDateTime.Day)

回答11:

Adding .Date to your date sets it to midnight (00:00).

MyDate.Date

Note The equivavalent SQL is CONVERT(DATETIME, CONVERT(DATE, @MyDate))

What makes this method so good is that it's both quick to type and easy to read. A bonus is that there is no conversion from strings.

I.e. To set today's date to 23:30, use:

DateTime.Now.Date.AddHours(23).AddMinutes(30)

You can of course replace DateTime.Now or MyDate with any date of your choice.

回答12:

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);

回答13:

Use Date.Add and add a New TimeSpan with the new time you want to add

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

回答14:

In fact, you can't change the time once it's created. But you can create it easily with many constructors: https://docs.microsoft.com/en-us/dotnet/api/system.datetime.-ctor?view=netframework-4.7.2

For example, if you want to create a DateTime changing Seconds, you can just do this:

DateTime now = DateTime.Now;
DateTime secondschanged = new DateTime(now.Year, now.Month, now.Day, now.Hour, now.Minute, yourseconds);

回答15:

Here is a method you could use to do it for you, use it like this

DateTime newDataTime = ChangeDateTimePart(oldDateTime, DateTimePart.Seconds, 0);

Here is the method, there is probably a better way, but I just whipped this up:

public enum DateTimePart { Years, Months, Days, Hours, Minutes, Seconds };
public DateTime ChangeDateTimePart(DateTime dt, DateTimePart part, int newValue)
{
    return new DateTime(
        part == DateTimePart.Years ? newValue : dt.Year,
        part == DateTimePart.Months ? newValue : dt.Month,
        part == DateTimePart.Days ? newValue : dt.Day,
        part == DateTimePart.Hours ? newValue : dt.Hour,
        part == DateTimePart.Minutes ? newValue : dt.Minute,
        part == DateTimePart.Seconds ? newValue : dt.Second
        );
}

回答16:

I have just come across this post because I had a similar issue whereby I wanted to set the time for an Entity Framework object in MVC that gets the date from a view (datepicker) so the time component is 00:00:00 but I need it to be the current time. Based on the answers in this post I came up with:

myEntity.FromDate += DateTime.Now.TimeOfDay;

回答17:

//The fastest way to copy time            

DateTime justDate = new DateTime(2011, 1, 1); // 1/1/2011 12:00:00AM the date you will be adding time to, time ticks = 0
DateTime timeSource = new DateTime(1999, 2, 4, 10, 15, 30); // 2/4/1999 10:15:30AM - time tick = x

justDate = new DateTime(justDate.Date.Ticks + timeSource.TimeOfDay.Ticks);

Console.WriteLine(justDate); // 1/1/2011 10:15:30AM
Console.Read();

回答18:

Since DateTime is immutable, a new instance has to be created when a date component needs to be changed. Unfortunately, there is no built-in functionality to set individual components of a DateTime instance.

Using the following extension methods

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);
}

you can set individual DateTime components like

var now = DateTime.Now;

now.SetSecond(0);

回答19:

What's wrong with DateTime.AddSeconds method where you can add or substract seconds?

回答20:

When you construct your DateTime object, use a constructor that allows you to specify time:

var myDateTime = new DateTime(2000, 01, 01, 13, 37, 42);  // 2000-01-01 13:37:42

If you already have a DateTime object and wish to change the time, uou can add minutes, hours or seconds to your DateTime using simple methods:

var myDateTime = new DateTime(2000, 01, 01);              // 2000-01-01 00:00:00
myDateTime = myDateTime.AddHours(13);                     // 2000-01-01 13:00:00
myDateTime = myDateTime.AddMinutes(37);                   // 2000-01-01 13:37:00
myDateTime = myDateTime.AddSecounds(42);                  // 2000-01-01 13:37:42

Notice how we have to "save" the result from each method call to the myDateTime variable. This is because the DateTime is immutable, and its methods simply create new instances with the extra hours/minutes/seconds added.

If you need to add both hours and minutes (and/or seconds) and the same time, you can simplify the code by adding a TimeSpan to the original DateTime instead:

var myDateTime = new DateTime(2000, 01, 01);              // 2000-01-01 00:00:00
myDateTime += new TimeSpan(13, 37, 42);                   // 2000-01-01 13:37:42

If you want to set absolute hours/minues/seconds, rather than adding to the existing values, you can use the aforementioned DateTime constructor, and reuse values for year/month/day from earlier:

myDateTime = new DateTime(myDateTime.Year, myDateTime.Month, myDateTime.Day,
                          20, 33, 19)                     // 2000-01-01 20:33:19

回答21:

Doesn't that fix your problems??

Dateime dt = DateTime.Now;
dt = dt.AddSeconds(10);

回答22:

I prefer this:

DateTime s = //get some datetime;
s = new DateTime(s.Year, s.Month,s.Day,s.Hour,s.Minute,0);

回答23:

 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;

        }

Use like this:

Console.WriteLine (DateTime.Now.ClearTimeFrom(eTimeFragment.hours))

this has to return: 2016-06-06 00:00:00.000

回答24:

  DateTime s;
//s = datevalue
                s = s.AddMilliseconds(10);
                s = s.AddMinutes(10);
                s = s.AddSeconds(10);
                s = s.AddHours(10);

you could add +ve/-ve values in parameter.

s.Add(new TimeSpan(1, 1, 1));

回答25:

The best solution is:

currdate.AddMilliseconds(currdate.Millisecond * -1).AddSeconds(currdate.Second * -1).AddMinutes(currdate.Minute * -1).AddHours(currdate.Hour * -1);

回答26:

Try this one

var NewDate = Convert.ToDateTime(DateTime.Now.ToString("dd/MMM/yyyy")+" "+"10:15 PM")/*Add your time here*/;

回答27:

here is a ghetto way, but it works :)

DateTime dt = DateTime.Now; //get a DateTime variable for the example
string newSecondsValue = "00";
dt = Convert.ToDateTime(dt.ToString("MM/dd/yyyy hh:mm:" + newSecondsValue));