NodaTime supports relative time display?

Question

I have a situation where the relative time is more important to a user than an absolute time. So it's more important to be able to quickly say "event happened 5 days and 5 hours ago" than "event happened at 1 PM CDT and it's 5 PM CST 5 days later now."

We store our dates in UTC and convert to display for the user:

pDateTime = DateTime.SpecifyKind(pDateTime, DateTimeKind.Utc);
DateTimeZone dateTimeZone = DateTimeZoneProviders.Tzdb[pCurrentUser.PreferredTimezone];
return Instant.FromDateTimeUtc(pDateTime).InZone(dateTimeZone).ToString("HH':'mm':'ss' 'MM'/'dd'/'yy' 'x", CultureInfo.InvariantCulture);

We'll be using NodaTime 1.2 when it's fully out and just used vanilla ToString before.

However, times using this pattern end up using the daylight status of the time as opposed to the current daylight status. This means that times look something like: 16:15:32 10/25/13 CDT even though we have now transitioned to CST.

It is an absolute measure of the time. This forces the user to do the logic: "How long ago was that? Is it daylight saving time now? If so, the difference is x. If not, I have to add or subtract an hour? That makes the difference y."

Meanwhile, a relative measure of the time would display 15:15:32 10/25/13 CST in the absence of DST. This forces the user to do no conversions and allows them to compute what that time means in context much easier.

In a display that has numerous dates, it can get tricky to do the absolute time logic over the entire set. Doing it once is tricky to get right. However, a friendly relative string like "posted 5 hours ago" also forces them to resolve both the date and time themselves - that information is still important.

A compromise might be to do the posted blank hours/minutes ago for the first 24 hours or to include both the friendly string and absolute time - these are both patterns I've seen done.

But ignoring those, is there a way in NodaTime to imbue a time with a specific daylight status in order to get times displaying in a relative context?

Answer 1

However, times using this pattern end up using the daylight status of the time as opposed to the current daylight status. This means that times look something like: 16:15:32 10/25/13 CDT even though we have now transitioned to CST.

Yes, and it should. Displaying a date/time with CST despite that date/time occurring in CDT would be very odd, IMO.

So it's more important to be able to quickly say "event happened 5 days and 5 hours ago" than "event happened at 1 PM CDT and it's 5 PM CST 5 days later now."

In that case you shouldn't be displaying a date/time at all, in my view. Convert both ZonedDateTime values to Instant, take the Duration between them, and then you can see that it's 5 days and 5 hours ago. (I can't remember how much help we provide with that - you may need to manually take the number of ticks and divide by NodaConstants.TicksPerStandardDay etc. Look at DurationPattern to see if it helps though.)

Alternatively, if you really want to display a date and time, but still easily be able to extract the difference between them mentally, two options suggest themselves:

• Use OffsetDateTime instead; there you could force the offsets to be the same, although I still think it would be odd to display an offset which wasn't actually the current offset in the zone you were observing the time in. Or you could just display the relevant offset at the time, so -5 for CST and -4 for CDT.
• Just display everything in UTC, so that daylight saving transitions are irrelevant.

Note that you can't get months between the two ZonedDateTime values, as we're dealing with an elapsed time (a duration) rather than calendar-logical arithmetic (a period).