c# - 计算一个月的最后一天

Question

给定 DateTime 和 DayOfWeek 应该返回该月最后一个 DayOfWeek 的日期。

例如2009 年 3 月 1 日和星期日将返回 2009 年 3 月 29 日

Answer 1

找不到方便的单线，但这个有效:

static DateTime LastDayOfWeekInMonth(DateTime day, DayOfWeek dow)
{
    DateTime lastDay = new DateTime(day.Year, day.Month, 1).AddMonths(1).AddDays(-1);
    DayOfWeek lastDow = lastDay.DayOfWeek;

    int diff = dow - lastDow;

    if (diff > 0) diff -= 7;

    System.Diagnostics.Debug.Assert(diff <= 0);

    return lastDay.AddDays(diff);
}