[英]Visual basic LINQ error
有人知道我为什么会有这个错误吗?
我收到以下错误:
你调用的对象是空的
这是有问题的LINQ。 感谢您的任何帮助。
Dim q = From line In seats
Let data = line.Split(New [Char]() {" "c}, StringSplitOptions.RemoveEmptyEntries) ' it occurs in this line '
Let seatA = data(0)
Let seatB = data(1)
Let seatC = data(2)
Let seatD = data(3)
Let seatE = data(4)
Let seatF = data(5)
Where seatA Is "."
Where seatB Is "."
Select seatA, seatF
如果将第一行更改为:
Dim windowSeatQuery = From line In seats.Where(function (s) s isnot nothing)
这表示席位列表中存在空值,并且上面的Where
lambda应该将其删除。
您的Where子句对我来说很奇怪。 您不应该使用=运算符,而不是:
Dim q = From line In seats
Let data = line.Split(New [Char]() {" "c}, StringSplitOptions.RemoveEmptyEntries) ' it occurs in this line '
Let seatA = data(0)
Let seatB = data(1)
Let seatC = data(2)
Let seatD = data(3)
Let seatE = data(4)
Let seatF = data(5)
Where seatA = "." AndAlso seatB = "." '<------ Use = on this line not Is
Select seatA, seatF
并且您确定每一行都用空格而不是其他空格分隔吗? 即使其中存在Is也不会导致Null Ref。
这是我的示例程序,似乎有效(在LinqPad中测试,该程序似乎不支持隐式的行连续字符):
Sub Main
Dim seats As New List(Of String)()
seats.Add("1 2 3 4 5 6")
seats.Add(". . 9 8 7 6")
seats.Add(". . 5 5 5 5")
seats.Add("1 2 3 4 5 6")
seats.Add(". . 2 4 6 8")
seats.Add("1 2 3 4 5 6")
Dim q = From line In seats _
Let data = line.Split(New [Char]() {" "c}, StringSplitOptions.RemoveEmptyEntries) _
Let seatA = data(0) _
Let seatB = data(1) _
Let seatC = data(2) _
Let seatD = data(3) _
Let seatE = data(4) _
Let seatF = data(5) _
Where seatA = "." AndAlso seatB = "." _
Select seatA, seatF
q.Dump()
End Sub
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.