# .Net时间计算函数，统计某一天是一年的第几周，这一周从哪天开始到哪天结束

/// <summary>

/// 计算某年第一周的天数
/// </summary>
/// <param name="dt">某年中的一个时间</param>
/// <returns></returns>
public static int DaysInFirstweekInYear(DateTime dt)
{
DateTime FirstDate = Convert.ToDateTime(string.Format("{0}-1-1", dt.Year));
int DayOfWeekInYear = DayOfWeek(FirstDate);
int DaysInFirstWeek = 8 - DayOfWeekInYear;
return DaysInFirstWeek;
}

/// <summary>
/// 一年中的第几周
/// </summary>
/// <param name="dt"></param>
/// <returns></returns>
public static int WeekOfYear(DateTime dt)
{
int days = DaysInFirstweekInYear(dt);
int dayofyear = dt.DayOfYear;
if (dayofyear < days) return 1;
else
{
int week2 = (int)Math.Ceiling((double)(dayofyear - days) / (double)7);
return week2 + 1;
}
}
/// <summary>
/// 传入某一天，输出这一周的起始日期
/// </summary>
/// <param name="dt"></param>
/// <returns></returns>
public static DateTime[] DatesIncludeDay(DateTime dt)
{
DateTime[] dts = new DateTime[2];
int dayofweek = DayOfWeek(dt);
return dts;
}
/// <summary>
/// 计算星期几，转换为数字
/// </summary>
/// <param name="dt">某天的日期</param>
/// <returns></returns>
public static int DayOfWeek(DateTime dt)
{
string strDayOfWeek = dt.DayOfWeek.ToString().ToLower();
int intDayOfWeek = 0;
switch (strDayOfWeek)
{
case "monday":
intDayOfWeek = 1;
break;
case "tuesday":
intDayOfWeek = 2;
break;
case "wednesday":
intDayOfWeek = 3;
break;
case "thursday":
intDayOfWeek = 4;
break;
case "friday":
intDayOfWeek = 5;
break;
case "saturday":
intDayOfWeek = 6;
break;
case "sunday":
intDayOfWeek = 7;
break;
}
return intDayOfWeek;

}

DateTime dt = Convert.ToDateTime("2013-1-6");
Dictionary<string, DateTime> dict = new Dictionary<string, DateTime>();
string str = "";
foreach(KeyValuePair<string,DateTime> kv in dict)
{
DateTime[] dts = Common.OperateText.DatesIncludeDay(kv.Value);
str = str + string.Format("{0},第{1}周,时间{2:yyyy-MM-dd},本周从{3:yyyy-MM-dd}到{4:yyyy-MM-dd} <br/>",kv.Key,Common.OperateText.WeekOfYear(kv.Value),kv.Value,dts[0],dts[1]);
}

Response.Write(str);

+ 订阅