///
///
///
/// 年（1 到 9999）
/// 周（1 到 53）
/// 确定首周的规则
/// 当此方法返回时，则包含参数 year 和 weeks 指定的周的开始日期的 System.DateTime 值；如果失败，则为 System.DateTime.MinValue。如果参数 year 或 weeks 超出有效范围，则操作失败。该参数未经初始化即被传递。
/// 当此方法返回时，则包含参数 year 和 weeks 指定的周的结束日期的 System.DateTime 值；如果失败，则为 System.DateTime.MinValue。如果参数 year 或 weeks 超出有效范围，则操作失败。该参数未经初始化即被传递。
///
public static bool GetDaysOfWeeks(int year, int weeks, CalendarWeekRule weekrule, out DateTime first, out DateTime last)
{
//初始化 out 参数
first = DateTime.MinValue;
last = DateTime.MinValue;
//不用解释了吧...
if (year < 1 | year > 9999)
return false;
//一年最多53周地球人都知道...
if (weeks < 1 | weeks > 53)
return false;
//取当年首日为基准...为什么？容易得呗...
DateTime firstCurr = new DateTime(year, 1, 1);
//取下一年首日用于计算...
DateTime firstNext = new DateTime(year + 1, 1, 1);
//将当年首日星期几转换为数字...星期日特别处理...ISO 8601 标准...
int dayOfWeekFirst = (int)firstCurr.DayOfWeek;
if (dayOfWeekFirst == 0) dayOfWeekFirst = 7;
//得到未经验证的周首日...
first = firstCurr.AddDays((weeks - 1) * 7 - dayOfWeekFirst + 1);
//周首日是上一年日期的情况...
if (first.Year < year)
{
switch (weekrule)
{
case CalendarWeekRule.FirstDay:
//不用解释了吧...
first = firstCurr;
break;
case CalendarWeekRule.FirstFullWeek:
//顺延一周...
first = first.AddDays(7);
break;
case CalendarWeekRule.FirstFourDayWeek:
//周首日距年首日不足4天则顺延一周...
if (firstCurr.Subtract(first).Days > 3)
{
first = first.AddDays(7);
}
break;
default:
break;
}
}
//得到未经验证的周末日...
last = first.AddDays(7).AddSeconds(-1);
switch (weekrule)
{
case CalendarWeekRule.FirstDay:
//周末日是下一年日期的情况...
if (last.Year > year)
last = firstNext.AddSeconds(-1);
else if (last.DayOfWeek != DayOfWeek.Monday)
last = first.AddDays(7 - (int)first.DayOfWeek).AddSeconds(-1);
break;
case CalendarWeekRule.FirstFourDayWeek:
//周末日距下一年首日不足4天则提前一周...
if (last.Year > year && firstNext.Subtract(first).Days < 4)
{
first = first.AddDays(-7);
last = last.AddDays(-7);
}
break;
default:
break;
}
return true;
}
///
///
///
///
private int GetWeekOfYear(DateTime dt)
{
GregorianCalendar gc = new GregorianCalendar();
return gc.GetWeekOfYear(dt, CalendarWeekRule.FirstDay, DayOfWeek.Monday);
}