Get list of time zones for a given offset in minutes using Noda Time

I am trying to design the following timezone solution using Noda Time:

A user would use a mobile app or web app to log in to the system. At the time of login a web API would be called with offset from UTC (let's say x minutes) as a parameter.

Now if the offset (x minutes) is different from offset (and timezone) saved in database, then the user would be shown a list of timezones which are x minutes away from UTC, so that they can select one out of them. The selected timezone and corresponding offset (x minutes) would then be saved in the database as the user's latest timezone.

How do I get a list of timezones which are x minutes away from UTC using Noda Time?

For example, if the user is +330 minutes away from UTC, then the user would get this prompt:

We have found that you're 5 hrs 30 minutes ahead of GMT. Please select your current timezone: "Asia/Colombo", "Asia/Kolkata"

2 Answers
2

You can do something like this:

TimeZoneInfo.GetSystemTimeZones()
.Where(x => x.GetUtcOffset(DateTime.Now).TotalMinutes == 330)


And now you have a collection of the time zones! You can replace DateTime.Now with some other date or a DateTimeOffset depending on your situation.

DateTime.Now

DateTimeOffset

In Noda Time, you can do this:

using NodaTime;
using NodaTime.TimeZones;

TzdbDateTimeZoneSource.Default.GetIds()
.Select(x => TzdbDateTimeZoneSource.Default.ForId(x))
.Where(x =>
x.GetUtcOffset(SystemClock.Instance.GetCurrentInstant()).ToTimeSpan().TotalMinutes == 330)


A slightly alternative approach to Sweeper's code, using a target offset instead of converting each offset to a TimeSpan, using a single computation of "now" (for consistent results) and using the IDateTimeZoneProvider.GetAllZones extension method.

TimeSpan

IDateTimeZoneProvider.GetAllZones

using System;
using System.Linq;
using NodaTime;
using NodaTime.Extensions;

class Test

static void Main()

// No FromMinutes method for some reason...
var target = Offset.FromSeconds(330 * 60);
var now = SystemClock.Instance.GetCurrentInstant();
var zones = DateTimeZoneProviders.Tzdb.GetAllZones()
.Where(zone => zone.GetUtcOffset(now) == target);
foreach (var zone in zones)

Console.WriteLine(zone.Id);





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