Question

I need to convert UTC date strings to DateTimeOffsets.

This must work with a timezone which differs from the computers timezone.
E.g. current computer timezone is +02:00, but I want to create a DateTimeOffset with offset -4:00.

I already read lot of questions here on stackoverflow, but none of them solved my problem.

That is what I need to do:

Input: “2012-11-20T00:00:00Z”

Output: DateTimeOffset with:

• UtcDateTime of 2012-11-20 00:00
• the correct Utc offset for the defined timezone (01:00 in this example)
• LocalDateTime: 2012-11-20 01:00 (= UtcDateTime + Offset)

Of course daylight saving must be taken into account.

edit:
To make things even clearer, please try to complete the following code snippet:

DateTimeOffset result;
const string dateString = "2012-11-20T00:00:00Z";
var timezone = TimeZoneInfo.FindSystemTimeZoneById("W. Europe Standard Time"); //this timezone has an offset of +01:00:00 on this date

//do conversion here

Assert.AreEqual(result.Offset, new TimeSpan(1, 0, 0));  //the correct utc offset, in this case +01:00:00
Assert.AreEqual(result.UtcDateTime, new DateTime(2012, 11, 20, 0, 0, 0)); //equals the original date
Assert.AreEqual(result.LocalDateTime, new DateTime(2012, 11, 20, 1, 0, 0));

Answer 1

Here is the solution you are looking for:

const string dateString = "2012-11-20T00:00:00Z";
TimeZoneInfo timezone = TimeZoneInfo.FindSystemTimeZoneById("W. Europe Standard Time"); //this timezone has an offset of +01:00:00 on this date

DateTimeOffset utc = DateTimeOffset.Parse(dateString);
DateTimeOffset result = TimeZoneInfo.ConvertTime(utc, timezone);
        
Assert.AreEqual(result.Offset, new TimeSpan(1, 0, 0));  //the correct utc offset, in this case +01:00:00
Assert.AreEqual(result.UtcDateTime, new DateTime(2012, 11, 20, 0, 0, 0)); //equals the original date
Assert.AreEqual(result.DateTime, new DateTime(2012, 11, 20, 1, 0, 0));

Note that you were incorrectly testing the .LocalDateTime property – which is always going to convert the result to the local time zone of the computer. You simply need the .DateTime property instead.