Question

我有以下模型，我将其加载到IList集合并运行Linq查询。我遇到的问题是Linq查询将OPCServer成员作为IEnumerable（Char）返回。有没有理由不返回基础字符串？

如果我用For Each迭代集合，那么它会按预期返回字符串。

我是否必须手动将其转换回工作代码部分中显示的内容？

模型

Friend Class OpcDataTags

    Public Property Host As String
    Public Property HostLive As Boolean
    Public Property OpcServer As String
    Public Property OpcChannel As String
    Public Property PlcDns As String
    Public Property PlcIP As String
    Public Property Zone As String
    Public Property DataBlock As String
    Public Property StartByte As Int16
    Public Property ByteSize As Int16
    Public Property DataType As String
    Public Property Subscribed As Boolean
    Public Property Description As String
    Public Property ArraySize As Nullable(Of Int32)
    Public Property Abbreviation As String
    Public Property PlcID As Int32

End Class

集合

Friend Property OpcTags As IList(Of OpcDataTags)

LinqQuery

Dim server = From o In OpcTags.First.OpcServer

工作代码

Dim result = From o In OpcTags.First.OpcServer
Dim server As String = New String(result.ToArray)

Answer 1

你真正想要实现的是：

' From LINQ's point of view, OpcTags is an IEnumerable< OpcDataTags >
Dim serverQuery = From o In OpcTags Select o.OpcServer
' And now you've narrowed it down to an IEnumerable< String >

Dim firstOne = serverQuery.First
' And now you're selecting the first String from that enumeration of strings

请注意，如果枚举不产生任何字符串，则会抛出异常。

如果这种情况是可能的，那么效果也会令人不愉快您可以使用FirstOrDefault代替

Dim firstOne_OrNothingIfNone = serverQuery.FirstOrDefault

String类实现IEnumerable< Char >，你实际上是强制它看起来像是更多值的来源（因此隐式地将其投射到最佳IEnumerable匹配，即IEnumerable< Char >）

Linq查询IList <t>字符串成员</t>

1 个答案: