How do I format a date with Dart?

问题:

I have an instance of DateTime and I would like to format that to a String. How do I do that? I want to turn the date into a string, something like "2013-04-20".

回答1:

You can use the intl package (installer) to format dates.

For en_US formats, it's quite simple:

import 'package:intl/intl.dart';

main() {
  var now = new DateTime.now();
  var formatter = new DateFormat('yyyy-MM-dd');
  String formatted = formatter.format(now);
  print(formatted); // something like 2013-04-20
}

There are many options for formatting. From the docs:

 ICU Name                   Skeleton
 --------                   --------
 DAY                          d
 ABBR_WEEKDAY                 E
 WEEKDAY                      EEEE
 ABBR_STANDALONE_MONTH        LLL
 STANDALONE_MONTH             LLLL
 NUM_MONTH                    M
 NUM_MONTH_DAY                Md
 NUM_MONTH_WEEKDAY_DAY        MEd
 ABBR_MONTH                   MMM
 ABBR_MONTH_DAY               MMMd
 ABBR_MONTH_WEEKDAY_DAY       MMMEd
 MONTH                        MMMM
 MONTH_DAY                    MMMMd
 MONTH_WEEKDAY_DAY            MMMMEEEEd
 ABBR_QUARTER                 QQQ
 QUARTER                      QQQQ
 YEAR                         y
 YEAR_NUM_MONTH               yM
 YEAR_NUM_MONTH_DAY           yMd
 YEAR_NUM_MONTH_WEEKDAY_DAY   yMEd
 YEAR_ABBR_MONTH              yMMM
 YEAR_ABBR_MONTH_DAY          yMMMd
 YEAR_ABBR_MONTH_WEEKDAY_DAY  yMMMEd
 YEAR_MONTH                   yMMMM
 YEAR_MONTH_DAY               yMMMMd
 YEAR_MONTH_WEEKDAY_DAY       yMMMMEEEEd
 YEAR_ABBR_QUARTER            yQQQ
 YEAR_QUARTER                 yQQQQ
 HOUR24                       H
 HOUR24_MINUTE                Hm
 HOUR24_MINUTE_SECOND         Hms
 HOUR                         j
 HOUR_MINUTE                  jm
 HOUR_MINUTE_SECOND           jms
 HOUR_MINUTE_GENERIC_TZ       jmv
 HOUR_MINUTE_TZ               jmz
 HOUR_GENERIC_TZ              jv
 HOUR_TZ                      jz
 MINUTE                       m
 MINUTE_SECOND                ms
 SECOND                       s

For non-en_US dates, you need to explicitly load in the locale. See https://www.dartdocs.org/documentation/intl/latest/intl/DateFormat-class.html for more info.

回答2:

This will work too:

DateTime today = new DateTime.now();
String dateSlug ="${today.year.toString()}-${today.month.toString().padLeft(2,'0')}-${today.day.toString().padLeft(2,'0')}";
print(dateSlug);

回答3:

This give you the date like in a social network : ["today","yesterday","dayoftheweek",etc..]

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 "thurdsday";
          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}';
      }
      return "";
    }

回答4:

You can also specify the date format like stated earlier: https://pub.dartlang.org/documentation/intl/latest/intl/DateFormat-class.html

import 'package:intl/intl.dart';
String formatDate(DateTime date) => new DateFormat("MMMM d").format(date);

Produces: March 4