Dart DateFormat inconsistency - flutter

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;
}
}
}