由于flutter常用的Datetime库不知道德国的区域设置——de、de、de_DE、de- de或任何其他组合都不知道，例如，如果您希望用人类可读的字符串编写月份名称或日期名称，我建议您使用以下代码。

安装pub flutter pub add date_format

String formattedDate = formatDate(DateTime(year, month, day),[dd,'. ', MM, ' ', yyyy], locale: GermanDateLocale());

要获得一个用户友好的字符串，包括日期和时间，你可以使用这个:

import 'package:intl/intl.dart';

main() {
  final DateTime someDateTime = DateTime(2017, 9, 7, 17, 30);
  final DateFormat formatter = DateFormat.yMMMd().add_jms();
  final String formatted = formatter.format(someDateTime);
  print(formatted); // Sep 7, 2017 5:30:00 PM (in the US)
}

这就给你提供了社交网络中的日期:[“今天”，“昨天”，“星期的哪一天”，等等。]

void main() {
      DateTime now = new DateTime(2018,6,26);
      print(date(now));
    }
    
    String date(DateTime tm) {
      DateTime today = new DateTime.now();
      Duration oneDay = new Duration(days: 1);
      Duration twoDay = new Duration(days: 2);
      Duration oneWeek = new Duration(days: 7);
      String month;
      switch (tm.month) {
        case 1:
          month = "january";
          break;
        case 2:
          month = "february";
          break;
        case 3:
          month = "march";
          break;
        case 4:
          month = "april";
          break;
        case 5:
          month = "may";
          break;
        case 6:
          month = "june";
          break;
        case 7:
          month = "july";
          break;
        case 8:
          month = "august";
          break;
        case 9:
          month = "september";
          break;
        case 10:
          month = "october";
          break;
        case 11:
          month = "november";
          break;
        case 12:
          month = "december";
          break;
      }
    
      Duration difference = today.difference(tm);
    
      if (difference.compareTo(oneDay) < 1) {
        return "today";
      } else if (difference.compareTo(twoDay) < 1) {
        return "yesterday";
      } else if (difference.compareTo(oneWeek) < 1) {
        switch (tm.weekday) {
          case 1:
            return "monday";
          case 2:
            return "tuesday";
          case 3:
            return "wednesday";
          case 4:
            return "thursday";
          case 5:
            return "friday";
          case 6:
            return "saturday";
          case 7:
            return "sunday";
        }
      } else if (tm.year == today.year) {
        return '${tm.day} $month';
      } else {
        return '${tm.day} $month ${tm.year}';
      }
    }

另一种方法，使用intl包。

创建DateTime的扩展:

date_time_extension.dart

import 'package:intl/date_symbol_data_local.dart';
import 'package:intl/intl.dart';

extension DateTimeExtension on DateTime {
  String format([String pattern = 'dd/MM/yyyy', String? locale]) {
    if (locale != null && locale.isNotEmpty) {
      initializeDateFormatting(locale);
    }
    return DateFormat(pattern, locale).format(this);
  }
}

导入你要使用DateTime类型的文件，你可以这样使用它:

DateTime.now().format();

DateTime.now().format('MM/yyyy');

DateTime.now().format('MM/yyyy', 'es');

如果不想添加另一个库，也可以使用此方法

  DateTime dateTime = DateTime.now();
  String YYYY_MM_DD = dateTime.toIso8601String().split('T').first;
  print(YYYY_MM_DD); //2020-11-23

如果有人想将字符串格式的日期转换为其他字符串格式，首先使用DateTime.parse("2019-09-30")，然后将其传递给DateFormat("date pattern").format()

dateFormate = DateFormat("dd-MM-yyyy").format(DateTime.parse("2019-09-30"));

参考:Dart -如何将简单的日期字符串格式从yyyy-MM-dd更改为dd-MM-yyyy