Convert Long to DateTime give false value

Question

I just tried to convert a date stored as a long value into a DateTime but it gives me the date {2/01/0001 7:35:22 PM} whereas it should be {23/09/2019 4:30:23} (GMT +10)

Here is the long value 1569220232761 created on initialising the object. Here is the code that returns 2/01/0001

SeshStart = new DateTime(CurrentSession.startDate, DateTimeKind.Local);

With CurrentSession.startDate equal 1569220232761.

Answer 1

What you have is a Unix Time, not the number of Ticks (which would be orders of magnitudes larger)

_{i.e 637,048,098,230,000,000 apposed to 1,569,220,232,761}

Unix time

Unix time (also known as Epoch time, POSIX time, seconds since the Epoch, or UNIX Epoch time) is a system for describing a point in time. It is the number of seconds that have elapsed since the Unix epoch, that is the time 00:00:00 UTC on 1 January 1970,

DateTime(Int64)

Initializes a new instance of the DateTime structure to a specified number of ticks.

Try something like this

public static DateTime UnixTimeToDateTime(long unixtime)
{
   var dtDateTime = new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc);
   return dtDateTime.AddMilliseconds(unixtime).ToLocalTime();
}

Answer 2

Because you are calling DateTime(Int64, DateTimeKind) overload and as stated;

Parameters

ticks

Int64

A date and time expressed in the number of 100-nanosecond intervals that have elapsed since January 1, 0001 at 00:00:00.000 in the Gregorian calendar.

As a Ticks, 1569220232761 is equal to Monday, 23 September 2019 06:30:32.761 GTM and you can calculate your value exactly how explained on How can I convert a Unix timestamp to DateTime and vice versa? question.

Also be aware, with .NET 4.6 version, two method introduced as DateTimeOffset.FromUnixTimeSeconds(Int64) and DateTimeOffset.ToUnixTimeSeconds.