How do I create a DateTime instance in a specific timezone? - dart

Question

I am calling a legacy service that returns all times in a string format assuming that the timezone is EST. How do I create a DateTime instance and specify that the timezone is EST? When I display the times to the user's I will translate to their device timezone.

Answer 1

I wrote a package for this. It's called Instant, and it can fetch the latest DateTime in any given zone worldwide. Take a detailed look at https://aditya-kishore.gitbook.io/instant/
The basic usage to get a DateTime in a timezone is fairly simple.
Note: I assume below that your legacy service delivers a String with format HH:MM in 24 hr time, and that it doesn't deliver a date. If any of the following is untrue, lemme know and I'll change the code sample.
List<int> _hourmin (String parse) {
List<int> timeinint = [];
if (parse.length == 5) {
//if parse is something like 10:00
timeinint.add(int.parse(parse.substring(0,2))); //Add hours (10)
timeinint.add(int.parse(parse.substring(3,5))); //Add minutes (0)
} //hours >= 10
if (parse.length == 4) {
//if parse is something like 4:06
timeinint.add(int.parse(parse.substring(0,1))); //Add hours (4)
timeinint.add(int.parse(parse.substring(2,4))); //Add minutes (6)
} //hours < 10
return timeinint;
}
DateTime utcDateTimeFromZone(
{#required String zone,
int year = 0,
int month = 0,
int day = 0,
int hour = 0,
int minute = 0,
int second = 0,
int millisecond = 0,
int microsecond = 0}) {
hour = (hour - timeZoneOffsets[zone].truncate()) % 24; //Convert to UTC from timezone
if (hour<0) {
hour = 24 + hour;
}
minute = (minute - ((timeZoneOffsets[zone]%1)*60).round()) % 60;
if (minute<0) {
minute = 60 + minute;
}
//Convert to UTC from timezone
DateTime inUTC = DateTime.utc(year, month, day, hour, minute, second, millisecond, microsecond); //Initialize in UTC time
return inUTC;
}
//We get an array containing the hours minutes
List<int> time = _hourmin("4:25"); //put your API call as the param here
//This is what you need
DateTime finished = utcDateTimeFromZone(zone: "EST", hour: time[0], minute: time[1]);
print(formatTime(time: finished.toLocal())); //1:25 for me, because I'm PST, but this works with any local timezone
Hope that clears it up!

Answer 2

The included DateTime class only supports the local timezone or UTC but no specific timezone.
https://pub.dartlang.org/packages/timezone would provide that but it looks like it needs an update for Dart 2.0.0
https://pub.dartlang.org/packages/time_machine is a newer one.