Dart DateFormat inconsistency

Question

I'm trying to parse date string that looks like this Feb0920221500 (month, day in month, year, hours, minutes). But when I use MMMddyyyyHmm pattern I always get a FormatException. Furthermore intl's DateFormat fails to parse back a date which it has formatted before:

import 'package:intl/intl.dart';

void main() {
  final dateFormat = DateFormat("MMMddyyyyHmm");
  final dateString = dateFormat.format(DateTime.now());
  print(dateString);
  final date = dateFormat.parse(dateString);
  print(date);
}

Output:

Feb0920221511
Uncaught Error: FormatException: Trying to read yyyy from Feb0920221511 at position 13

What am I doing wrong?

Answer 1

You are running into this issue: https://github.com/dart-lang/intl/issues/210

TL/DR: Both methods are not designed to work fully reversible, if I understood the package maintainers correctly.

Try to introduce field separators like a space or a dot as a workaround:

  final dateFormat = DateFormat("MMM dd yyyy H mm");
  final dateString = dateFormat.format(DateTime.now());
  print(dateString);
  print(dateFormat.parseStdaterict(dateString));

If the format of the given date String cannot be changed, you still have the possibility to make it work with a hack like this. Just make sure to handle errors gracefully.

import 'package:intl/intl.dart';

Future<void> main() async {
  final parsedDate = 'Feb0920221511'.parseToDate();
  print(parsedDate.toIso8601String());
}

extension CustomDateParser on String {
  DateTime parseToDate() {
    try {
      final month = substring(0, 3);
      final day = substring(3, 5);
      final year = substring(5, 9);
      final hour = substring(9, 11);
      final minute = substring(11, 13);

      final paddedDateString = '$month $day $year $hour $minute';
      final dateFormat = DateFormat('MMM dd yyyy H mm');
      return dateFormat.parse(paddedDateString);
    } catch (e) {
      // handle error
      print(e);
      rethrow;
    }
  }
}