firstDayInNextMonth method

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

下月第一天

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

Implementation

DateTime firstDayInNextMonth([int firstDay = 1]) {
  return lastDayInMonth(firstDay).add(Duration(days: 1));
}