DateTime错误从0小时减去

Question

Using C# DateTime, I'd like to subtract a time past 0 (or midnight). However, I get an error when doing so. I'm trying to create a timeline where you can zoom in and out and scroll through the times. I get the following error: "The added or subtracted value results in an un-representable DateTime."

I guess DateTime doesn't know how to wrap back around from 0 to 23? How do I get around this?

Answer 1

If you subtract a TimeSpan from a DateTime , it will "wrap around" past midnight:

> var d1 = DateTime.Parse("4/11/2012 12:30:00 AM");
> var d2 = d1.Subtract(new TimeSpan(1, 15, 0));
> 
> d2
[4/10/2012 11:15:00 PM]

Answer 2

My guess is that you're using the date which starts at DateTime.MinValue . If you subtract time such that it would go before DateTime.MinValue , you'll get that exception.

// This is equal to DateTime.MinValue - maybe you're doing this?
DateTime date = new DateTime();
// Bang
date = date.AddHours(-1);

If you really want a "just a time" representation, consider using Noda Time , my pseudo-port of Joda Time with a rather richer type system than just DateTime .