1 /// <summary> 2 /// 获得今天是今年的第几周 3 /// </summary> 4 /// <param name="year"></param> 5 /// <returns></returns> 6 public string GetWeekOfYear(DateTime today) 7 { 8 int days = today.DayOfYear; 9 int remainder = days % 7; 10 if (remainder == 0) 11 return Convert.ToString(days / 7); 12 else 13 return Convert.ToString(days / 7 + 1); 14 }
-------------上面的代码没有考虑到当年的1月1号，并非是周一，所以算出来的会有误差
下面是参考博客园唔愛吃蘋果的代码。
1 public string GetWeekOfYear(DateTime today) 2 { 3 int weeknow = Convert.ToInt32(today.DayOfWeek);//today是周几 4 int daydiff = (-1) * (weeknow + 1);//今日与上周末的天数差 5 int days = today.AddDays(daydiff).DayOfYear;//上周末是本年第几天 6 int weeks = days / 7; 7 if (days % 7 != 0) 8 { 9 weeks++; 10 } 11 //此时，weeks为上周是本年的第几周 12 return Convert.ToString(weeks + 1); 13 }
他这边就巧妙的用上周末的来计算之前的周数
可是也存在比如本年的1月1号是周三，那么上周的周末是去年的，导致计算出错。
再加入判断，修改后代码如下：
1 /// <summary> 2 /// 获得今天是今年的第几周 3 /// </summary> 4 /// <param name="today"></param> 5 /// <returns></returns> 6 public string GetWeekOfYear(DateTime today) 7 { 8 int NewYear = Convert.ToInt32(today.Year); //今年的年份 9 int weeknow = Convert.ToInt32(today.DayOfWeek);//today是周几 10 int daydiff = (-1 * weeknow);//今日与上周末的天数差 11 int days = today.AddDays(daydiff).DayOfYear;//上周末是本年第几天 12 int OldYear = Convert.ToInt32(today.AddDays(daydiff).Year); //上周末的年份 13 if (NewYear == OldYear) 14 { 15 int weeks = days / 7; 16 if (days % 7 != 0) 17 { 18 weeks++; 19 } 20 //此时，weeks为上周是本年的第几周 21 return Convert.ToString(weeks + 1); 22 } 23 else 24 return "1"; 25 }