如何从DateTime Dart对象获取一年中的某一天,一年中的一周

Question

我需要从飞镖DateTime对象获取一年中的一天(第1天是1月1日),一年中的一周和一年中的一个月.

我没有找到任何可用的库.任何的想法 ？

Answer 1

一年中的一天

final date = someDate;
final diff = now.difference(new DateTime(date.year, 1, 1, 0, 0));
final diffInDays = diff.inDays;

一周的一周

final date = someDate;
final startOfYear = new DateTime(date.year, 1, 1, 0, 0);
final firstMonday = startOfYear.weekday;
final daysInFirstWeek = 8 - firstMonday;
final diff = date.difference(startOfYear);
var weeks = ((diff.inDays - daysInFirstWeek) / 7).ceil();
// It might differ how you want to treat the first week
if(daysInFirstWeek > 3) {
  weeks += 1;
}

一年中的一个月

final monthOfYear = new DateTime.now().month;

警告:这不是经过实战考验的代码.

Answer 2

一年中的第几周：

/// Calculates week number from a date as per https://en.wikipedia.org/wiki/ISO_week_date#Calculation
int weekNumber(DateTime date) {
  int dayOfYear = int.parse(DateFormat("D").format(date));
  return ((dayOfYear - date.weekday + 10) / 7).floor();
}

其余的可通过DateFormat（intl包的一部分）获得。

Answer 3

试试这个非常简单的 dart 包，Jiffy。下面的代码会有所帮助

获取一年中的日期

// This will return the day of year from now
Jiffy().dayOfYear; // 295

// You can also pass in a dateTime object
Jiffy(DateTime(2019, 1, 3)).dayOfYear; // 3

获得一年中的一周

Jiffy().week; // 43

// You can also pass in an Array or Map
Jiffy([2019, 1, 3]).week; // 1

获得一年中的月份

Jiffy().month; // 10

Jiffy({
    "year": 2019,
    "month": 1,
    "day": 3
  }).month; // 1

希望这个答案有帮助

Answer 4

根据 ISO 8601 的周数

int isoWeekNumber(DateTime date) {
    int daysToAdd = DateTime.thursday - date.weekday;
    DateTime thursdayDate = daysToAdd > 0 ? date.add(Duration(days: daysToAdd)) : date.subtract(Duration(days: daysToAdd.abs()));
    int dayOfYearThursday = dayOfYear(thursdayDate);
    return 1 + ((dayOfYearThursday - 1) / 7).floor();
}
int dayOfYear(DateTime date) {
    return date.difference(DateTime(date.year, 1, 1)).inDays;
}

Answer 5

这是我在Dart中实施的ISO 8601年度周：

int getWeekOfYear(DateTime date) {
  final weekYearStartDate = getWeekYearStartDateForDate(date);
  final dayDiff = date.difference(weekYearStartDate).inDays;
  return ((dayDiff + 1) / 7).ceil();
}

DateTime getWeekYearStartDateForDate(DateTime date) {
  int weekYear = getWeekYear(date);
  return getWeekYearStartDate(weekYear);
}

int getWeekYear(DateTime date) {
  assert(date.isUtc);

  final weekYearStartDate = getWeekYearStartDate(date.year);

  // in previous week year?
  if(weekYearStartDate.isAfter(date)) {
    return date.year - 1;
  }

  // in next week year?
  final nextWeekYearStartDate = getWeekYearStartDate(date.year + 1);
  if(isBeforeOrEqual(nextWeekYearStartDate, date)) {
    return date.year + 1;
  }

  return date.year;
}

DateTime getWeekYearStartDate(int year) {
  final firstDayOfYear = DateTime.utc(year, 1, 1);
  final dayOfWeek = firstDayOfYear.weekday;
  if(dayOfWeek <= DateTime.thursday) {
    return addDays(firstDayOfYear, 1 - dayOfWeek);
  }
  else {
    return addDays(firstDayOfYear, 8 - dayOfWeek);
  }
}

请注意，“周年”并不总是日历年，也可以是之前或之后的一年：

void printWeekOfYear(DateTime date) {
  print('week ${getWeekOfYear(date)} in year ${getWeekYear(date)}');
}

printWeekOfYear(DateTime.utc(2017, 1, 1));
// --> week 52 in year 2016

printWeekOfYear(DateTime.utc(2019, 12, 31));
// --> week 1 in year 2020

Answer 6

Dart SDK2.8.4 及更高版本：
一年中的某一天，没有软件包：

void main(){
  final now = new DateTime.now();
  final todayInDays = now.difference(new DateTime(now.year,1,1,0,0)).inDays; //return 157
}

参考（官方）> inDays，来自 Dart 官方文档