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How to check if a timespan in negative. C#

The title says it all. I'm subtracting two DateTimes and I want to see if the returned Timespan is negative. How do I do this?
// dt1 and dt2 are DateTimes.
TimeSpan ts = dt1.Subtract(dt2);
ts.isNegative() // or something like that

TimeSpan has a Compare method on it, or you can do < TimeSpan.Zero or you could have just compared the two DateTimes in the first place and skipped creating the TimeSpan entirely.

Subtract days from a DateTime

I have the following code in my C# program.
DateTime dateForButton = DateTime.Now;
dateForButton = dateForButton.AddDays(-1); // ERROR: un-representable DateTime
Whenever I run it, I get the following error:
The added or subtracted value results in an un-representable DateTime.
Parameter name: value
Iv'e never seen this error message before, and don't understand why I'm seeing it. From the answers Iv'e read so far, I'm lead to believe that I can use -1 in an add operation to subtract days, but as my question shows this is not the case for what I'm attempting to do.

DateTime dateForButton = DateTime.Now.AddDays(-1);

That error usually occurs when you try to subtract an interval from DateTime.MinValue or you want to add something to DateTime.MaxValue (or you try to instantiate a date outside this min-max interval). Are you sure you're not assigning MinValue somewhere?

You can do:
DateTime.Today.AddDays(-1)

You can use the following code:
dateForButton = dateForButton.Subtract(TimeSpan.FromDays(1));

The dateTime.AddDays(-1) does not subtract that one day from the dateTime reference. It will return a new instance, with that one day subtracted from the original reference.
DateTime dateTime = DateTime.Now;
DateTime otherDateTime = dateTime.AddDays(-1);

Instead of directly decreasing number of days from the date object directly, first get date value then subtract days. See below example:
DateTime SevenDaysFromEndDate = someDate.Value.AddDays(-1);
Here, someDate is a variable of type DateTime.

The object (i.e. destination variable) for the AddDays method can't be the same as the source.
Instead of:
DateTime today = DateTime.Today;
today.AddDays(-7);
Try this instead:
DateTime today = DateTime.Today;
DateTime sevenDaysEarlier = today.AddDays(-7);

I've had issues using AddDays(-1).
My solution is TimeSpan.
DateTime.Now - TimeSpan.FromDays(1);

Using AddDays(-1) worked for me until I tried to cross months. When I tried to subtract 2 days from 2017-01-01 the result was 2016-00-30. It could not handle the month change correctly (though the year seemed to be fine).
I used date = Convert.ToDateTime(date).Subtract(TimeSpan.FromDays(2)).ToString("yyyy-mm-dd");
and have no issues.

Convert Date to Milliseconds

I am working with Visual Studio 2010, MVC 3 and C#. I am creating some highcharts and need to have the x-axis be a date. I am pulling the dates from a database and adding them to and array that will then be passed to highcharts. I think highcharts requires the dates to be in millisecond format. Ho do I go about converting a DateTime of '12/20/2011 5:10:13 PM" for example to milliseconds?

Once you figure out what you want to calculate milliseconds from, you can just take one DateTime object from another to get a TimeSpan object. From TimeSpan you can get TotalMilliseconds.
In other words, if start and end are DateTime objects, you can do this:
double milliseconds = (end - start).TotalMilliseconds;

You can use the DateTime.Ticks property and convert the value to milliseconds.
The value of this property represents the number of 100-nanosecond intervals that have elapsed since 12:00:00 midnight, January 1, 0001, which represents DateTime.MinValue. It does not include the number of ticks that are attributable to leap seconds.
A single tick represents one hundred nanoseconds or one ten-millionth of a second. There are 10,000 ticks in a millisecond.

The .Ticks in C# DateTime gives you the value of any time in ticks. You can thereafter convert to milliseconds as shown below:
long dateticks = DateTime.Now.Ticks;
long datemilliseconds = dateticks / TimeSpan.TicksPerMillisecond;

DateTime[] dates = ;
var minDate = dates.Min();
var msDates = dates.Select(date => (date - minDate).TotalMilliseconds).ToArray();

Silverlight convert datePicker to DateTime

can someone tell me how to conver DatePicker value to DateTime value...
I have this variables:
DateTime now = DateTime.Now;
DatePicker rd = rd_datePicker;
I would like to get difference in days betwen this two dates, can you help me with this too?

Have you tried using DatePicker.SelectedDate?
Once you've got the two DateTime values (you may want to use DateTime.Today instead of DateTime.Now) you can subtract one from the other to get a TimeSpan, and then use TimeSpan.TotalDays to find out the number of days in the period.
(As DateTime is effectively a "local" representation, you don't need to worry about time zones or variable day lengths in this particular case. Date and time arithmetic in general is rather tricky...)

DatePicker dp = new DatePicker();
DateTime dt=new DateTime();
dp.Text = dt.Date.ToString("yyyy/MM/dd");

How do you calculate accumulative time in C#?

I want to calculate the time span between 2 times which I saved in a database.
So literally I want to know the length of time between the 2 values.
14:10:20 - 10:05:15 = 02:05:05
So the result would be 02:05:05.
How would I be able to achieve this using C#?
14:10:20 is the format I saved it in in my database.

Read the two time values into TimeSpan variables, then perform a .Subtract() on the bigger TimeSpan variable to get the TimeSpan result.
E.g. TimeSpan difference = t1.Subtract(t2);.

Your first step will be to get the timevalues stored in your database into .NET DateTime structs.
If you stored them as SQL-DateTime values in the database you can get them directly as DateTime. It would look something like this:
SQLCommand getTimeCommand = new SQLCommand("SELECT time FROM table", dbConnection);
SQLDataReader myReader = getTimeCommand.ExecuteReader();
while (myReader.Read())
{
DateTime time = myReader.GetDateTime(0);
}
myReader.Close();
Your implementation might differ, refer to the ADO.NET documentation in the MSDN library.
If you already got a string representing the time you can parse the string into a DateTime using the static methods
DateTime.Parse
or
DateTime.ParseExact
In your case you might need to use ParseExact, which can pe provided with a format-string defining how to read the string. Examples should be found in the MSDN library.
Durations in .NET are stored inside a TimeSpan struct. Getting the elapsed time between to datetimes is easy:
DateTime time1, time2; //filled with your timevalues from the db
TimeSpan elapsed = d2 - d1;
elapsed now contains the timespan between the two DateTimes. There are several members for the struct to access the TimeSpan. Look into the MSDN-Library to find the ones you need.

DateTime objects support the "-" operator so you can just read your times into such objects and subtract them. To test, check this out:
DateTime then = DateTime.Now;
Thread.Sleep(500);
DateTime now = DateTime.Now;
TimeSpan time = now - then;
MessageBox.Show(time.ToString());