firstDayInWeek method

DateTime firstDayInWeek([
  1. int firstWeekDay = 1
])

本周第一天

firstWeekDay - 设置每周起始日, assert(firstWeekDay > 0 && firstWeekDay < 7)

Implementation

DateTime firstDayInWeek([int firstWeekDay = 1]) {
  assert(firstWeekDay > 0 && firstWeekDay < 7);
  DateTime _day =
      this.subtract(Duration(days: (7 + weekday - firstWeekDay) % 7));
  return DateTime(_day.year, _day.month, _day.day);
}