MichaelMarner / timezone

Time zone database and time zone aware DateTime object for Dart.

TimeZone

This package provides the IANA time zone database and time zone aware DateTime class, TZDateTime.

The current Time Zone database version is 2019a. See the announcement for details.

Initialization

TimeZone objects require time zone data, so the first step is to load one of our time zone databases.

We provide two different APIs to load a database: one for browsers and one standalone environments.

Initialization for browser environment

Import package:timezone/browser.dart library and run async function Future initializeTimeZone([String path]).

import 'package:timezone/browser.dart';

Future<Null> setup() async {
  final detroit = getLocation('America/Detroit');
  final now = new TZDateTime.now(detroit);
});

Initialization for standalone environment

Import package:timezone/standalone.dart library and run async function Future initializeTimeZone([String path]).

import 'package:timezone/standalone.dart';

Future<Null> setup() async {
  await initializeTimeZone();
  final detroit = getLocation('America/Detroit');
  final now = new TZDateTime.now(detroit);
}

Local Location

By default, when library is initialized, local location will be UTC.

To overwrite local location you can use setLocalLocation(Location location) function.

Future<Null> setup() async {
  await initializeTimeZone();
  final detroit = getLocation('America/Detroit');
  setLocalLocation(detroit);
}

Initialization for Flutter Apps

Flutter apps need to be initialized slightly differently, as the timezone database file needs to be bundled with your application assets.

Add the database to your pubspec.yaml

Under the assets section of your application's pubspec.yaml, add a reference to the timezone database file:

assets:
  - packages/timezone/data/2019a.tzf

If you don't want to have to change the bundled filename when this library updates, you can have flutter bundle the directory instead:

assets:
  - packages/timezone/data/

Initialize the library in your application startup

The database needs to be loaded before using the library. A good place to do this is in your app's main function before running the Flutter app. Here we load the database file from assets, and initialize the library.

import 'package:timezone/timezone.dart';

void main() async {
  var byteData = await rootBundle
      .load('packages/timezone/data/${tzDataDefaultFilename}');
  initializeDatabase(byteData.buffer.asUint8List());
  runApp(MyApp());
}

API

Location

Each location in the database represents a national region where all clocks keeping local time have agreed since 1970. Locations are identified by continent or ocean and then by the name of the location, which is typically the largest city within the region. For example, America/New_York represents most of the US eastern time zone; America/Phoenix represents most of Arizona, which uses mountain time without daylight saving time (DST); America/Detroit represents most of Michigan, which uses eastern time but with different DST rules in 1975; and other entries represent smaller regions like Starke County, Indiana, which switched from central to eastern time in 1991 and switched back in 2006.

The tz database

Get location by Olsen time zone ID

final detroit = getLocation('America/Detroit');

We don't provide any functions to get locations by time zone abbreviations because of the ambiguities.

Alphabetic time zone abbreviations should not be used as unique identifiers for UTC offsets as they are ambiguous in practice. For example, "EST" denotes 5 hours behind UTC in English-speaking North America, but it denotes 10 or 11 hours ahead of UTC in Australia; and French-speaking North Americans prefer "HNE" to "EST".

The tz database

TimeZone

TimeZone objects represents time zone and contains offset, DST flag, and name in the abbreviated form.

final timeInUtc = new DateTime.utc(1995, 1, 1);
final timeZone = detroit.timeZone(timeInUtc.millisecondsSinceEpoch);

TimeZone aware DateTime

The TZDateTime class implements the DateTime interface from dart:core, and contains information about location and time zone.

final date = new TZDateTime(detroit, 2014, 11, 17);

Converting DateTimes between time zones

To convert between time zones, just create a new TZDateTime object using from constructor and pass Location and DateTime to the constructor.

final localTime = new DateTime(2010, 1, 1);
final detroitTime = new TZDateTime.from(time, detroit);

This constructor supports any objects that implement DateTime interface, so you can pass a native DateTime object or our TZDateTime.

Time Zone databases

We are using IANA Time Zone Database to build our databases.

We are currently building three different database variants:

• default (doesn't contain deprecated and historical zones with some exceptions like US/Eastern). 351kb
• all (contains all data from the IANA time zone database). 433kb
• 2010-2020 (default database that contains historical data from 2010 until 2020). 86kb

Updating Time Zone databases

Script for updating Time Zone database, it will automatically download the IANA time zone database and compile into our native format.

$ pub run tool/get -s 2014h

The argument -s is for specifying source version.