lastDayInMonth method

DateTime lastDayInMonth([
  1. int firstDay = 1
])

当月最后一天

firstDay - 每月起算日期，assert(firstDay > 0 && firstDay < 29)

Implementation

DateTime lastDayInMonth([int firstDay = 1]) {
  assert(firstDay > 0 && firstDay < 29);
  if (firstDay <= day) {
    return DateTime(
        year,
        month + 1,
        min(firstDay - 1,
            DateTime(year, month + 2).subtract(Duration(days: 1)).day));
  } else {
    return DateTime(
        year,
        month,
        min(firstDay - 1,
            DateTime(year, month + 1).subtract(Duration(days: 1)).day));
  }
}