flutter 获取今天是这个月第几周

int getWeekIndex() {
    var time = DateTime.now(); //当前时间
    int day = time.day; //今天几号：1~31
    int week = time.weekday; // 今天周几：1~7
    int weekIndex = 0;
    for (int i=day; i>=1; i--) {
      week--;
      if (week <= 0) { // 到了周天，要+1
        week = 7;
        weekIndex++;
      }
    }
    if (week != 7) { // 第一天不是周日的话，要+1
      weekIndex++;
    }
    return weekIndex;
  }