取当前日期是在一年中的第几周

C#里有GregorianCalendar这样一个类，只需要两行代码：

using System.Globalization;

GregorianCalendar gc = new GregorianCalendar();
int weekOfYear = gc.GetWeekOfYear(DateTime.Now, CalendarWeekRule.FirstDay, DayOfWeek.Monday);

写成通用的方法，获取某一日期是该年中的第几周

using System.Globalization;

/// <summary>
/// 获取某一日期是该年中的第几周
/// </summary>
/// <param name="dt">日期</param>
/// <returns>该日期在该年中的周数</returns>
private int GetWeekOfYear(DateTime dt)
{
GregorianCalendar gc = new GregorianCalendar();
return gc.GetWeekOfYear(dt, CalendarWeekRule.FirstDay, DayOfWeek.Monday);
}

以前还在CSDN上遇到这样一个问题，就是计算某一年有多少周，同样可以用这个类的方法来解决

using System.Globalization;

/// <summary>
/// 获取某一年有多少周
/// </summary>
/// <param name="year">年份</param>
/// <returns>该年周数</returns>
private int GetWeekAmount(int year)
{
DateTime end = new DateTime(year, 12, 31); //该年最后一天
System.Globalization.GregorianCalendar gc = new GregorianCalendar();
return gc.GetWeekOfYear(end, CalendarWeekRule.FirstDay, DayOfWeek.Monday); //该年星期数
}