dart - Dart:日期添加不一致

Question

向2020-09-18添加一天时，我得到2020-09-19 00:00:00.000，但是当我添加3天(或更多天)时，我得到2020-09-20 23:00:00.000，哪一个先获得23小时？第二次加3天到18是21而不是20!
问题是什么？

void main() {
  var dateOne = DateTime.parse('2020-09-18 00:00:00.000');
  var dateTwo = dateOne.add(Duration(days: 1 )); // 2020-09-19 00:00:00.000
  var dateThree = dateOne.add(Duration(days: 3 )); // 2020-09-20 23:00:00.000
  print(dateTwo);
  print(dateThree);
}

Answer 1

原因是Daylight Saving Time，因为add方法只理解API中记录的秒，因此Duration在使用前会转换为秒:

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
正如您自己提到的那样，您可以改用UTC来解决此问题。