C# Linq语句中的序列不包含匹配元素错误
我试图调试我的方法,但我不知道它出了什么问题 有时它会抛出一个错误,有时它会没事。我不知道怎么了 以下是我的方法:C# Linq语句中的序列不包含匹配元素错误,c#,.net,linq,C#,.net,Linq,我试图调试我的方法,但我不知道它出了什么问题 有时它会抛出一个错误,有时它会没事。我不知道怎么了 以下是我的方法: private void GetWorkingWeek(int month, int year) { var cal = System.Globalization.CultureInfo.CurrentCulture.Calendar; var daysInMonth = Enumerable.Range(1, cal.GetDaysIn
private void GetWorkingWeek(int month, int year)
{
var cal = System.Globalization.CultureInfo.CurrentCulture.Calendar;
var daysInMonth = Enumerable.Range(1, cal.GetDaysInMonth(year, month));
var listOfWorkWeeks = daysInMonth
.Select(day => new DateTime(year, month, day))
.GroupBy(d => cal.GetWeekOfYear(d, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday))
.Select(g => Tuple.Create(g.Key, g.First(), g.Last(d => d.DayOfWeek != DayOfWeek.Saturday && d.DayOfWeek != DayOfWeek.Sunday)))
.ToList();
foreach (var weekGroup in listOfWorkWeeks)
{
Console.WriteLine("Week{0} = {1} {2} to {1} {3}"
, weekNum++
, System.Globalization.CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(month)
, weekGroup.Item2.Day
, weekGroup.Item3.Day);
}
}
这是出现错误的行:
var listOfWorkWeeks = daysInMonth
.Select(day => new DateTime(year, month, day))
.GroupBy(d => cal.GetWeekOfYear(d, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday))
.Select(g => Tuple.Create(g.Key, g.First(), g.Last(d => d.DayOfWeek != DayOfWeek.Saturday && d.DayOfWeek != DayOfWeek.Sunday)))
.ToList();
这就是错误:
InvalidOperationException : Sequence contains no matching element
尝试使用FirstOrDefault
和LastOrDefault
而不是First
和Last
,如果没有元素与作为参数提供的lambda表达式匹配,这些方法将返回调用它们的类型的默认值
在
g.FirstOrDefault()
的情况下,如果g为空,将返回默认值;在g.FirstOrDefault的情况下(d=>d.DayOfWeek!=DayOfWeek.Saturday&&d.DayOfWeek!=DayOfWeek.Sunday)
如果所有天都是星期六或星期日,将返回默认值。我猜是第一天()还是最后一天()方法抛出错误。您可以尝试替换FirstOrDefault()和LastOrDefault(),这将为空数据集返回null,而不是触发异常。解释可能重复1+
var listOfWorkWeeks = daysInMonth
.Select(day => new DateTime(year, month, day))
.GroupBy(d => cal.GetWeekOfYear(d, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday))
.Select(g => Tuple.Create(g.Key, g.FirstOrDefault(), g.LastOrDefault(d => d.DayOfWeek != DayOfWeek.Saturday && d.DayOfWeek != DayOfWeek.Sunday)))
.ToList();