CODEWITHSUNDEEP
dart
Jaczura Zoltán
Jaczura Zoltán

Reputation: 343

dart DateTime.add add 1 hours from a specific date

I Would have a dart questions.

print(DateTime(2020,03,12).add(new Duration(days: 17)));
print(DateTime(2020,03,12).add(new Duration(days: 18)));

Results:

2020-03-29 00:00:00.000

2020-03-30 01:00:00.000

I don't understand the second result. Why 01:00:00?

This is the result running on Flutter test and dartpad.dev online, although if I run it from flutter application it shows 00:00:00 correctly. Why?

print(DateTime(2019,03,12).add(new Duration(days: 17)));

print(DateTime(2019,03,12).add(new Duration(days: 18)));

shows:

2019-03-29 00:00:00.000

2019-03-30 00:00:00.000

print(DateTime(2021,03,12).add(new Duration(days: 17)));

print(DateTime(2021,03,12).add(new Duration(days: 18)));

shows:

2021-03-29 01:00:00.000

2021-03-30 01:00:00.000

Upvotes: 2

Views: 3490

Answers (2)

Bobin
Bobin

Reputation: 445

The recommended way to add 1 day to a DateTime is like this:

DateTime other = ...;
DateTime nextDay = DateTime(other.year, other.month, other.day + 1, other.hour, other.minute)

You can write an extension method like this:

extension DateTimeExtension on DateTime {
  DateTime addDays(int days) => DateTime(year, month, day + days, hour, minute);
}

Also works when day + days is greater than 31.

Upvotes: 1

julemand101
julemand101

Reputation: 31219

The reason is properly Daylight Saving Time since the add method does only understand seconds as documented in the API and the Duration are therefore converted to seconds before it is used:

Notice that the duration being added is actually 50 * 24 * 60 * 60 seconds. If the resulting DateTime has a different daylight saving offset than this, then the result won't have the same time-of-day as this, and may not even hit the calendar date 50 days later.

Be careful when working with dates in local time.

https://api.dart.dev/stable/2.7.2/dart-core/DateTime/add.html

Upvotes: 2

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