Question

I have the following ASP.Net MVC Controller method:

public ActionResult DoSomething(DateTime utcDate)
{
   var localTime = utcDate.ToLocalTime();
}

The problem is that localTime will have the exact same value as utcDate. I assume this is because utcDate doesn’t know it has a UTC value. So my question is how can I convert utcDate (which I KNOW is UTC) into local?

Answer 1

If you know the DateTime contains a UTC value, you can use the following:

DateTime iKnowThisIsUtc = whatever;
DateTime runtimeKnowsThisIsUtc = DateTime.SpecifyKind(
    iKnowThisIsUtc,
    DateTimeKind.Utc);
DateTime localVersion = runtimeKnowsThisIsUtc.ToLocalTime();

For example, in my current application, I create timestamps in my database with SQL’s utcnow, but when I read them into my C# application the Kind proeprty is always Unknown. I created a wrapper function to read the timestamp, deliberately set its Kind to Utc, and then convert it to local time – essentially as above.

Note that DateTime.ToLocalTime() only doesn’t affect the value if one (or both) of the following holds:

• The DateTime‘s Kind property is DateTimeKind.Local
• Your local timezone is such that “no change” is the correct conversion

I think we can assume the second point isn’t true. Thus it seems that iKnowThisIsUtc‘s Kind property is set to Local already. You need to figure out why whatever is supplying you with these DateTimes thinks they are local.