Question

请参阅以下代码：

Public Shared Sub LinqTest()
        Dim t1 As New TestPerson
        t1.id = 1
        t1.name = "Ian"

        Dim t2 As New TestPerson
        t2.id = 2
        t2.name = "Lauren"

        Dim list As List(Of TestPerson) = New List(Of TestPerson)
        list.Add(t1)
        list.Add(t2)

        Dim list2 As List(Of TestPerson) = New List(Of TestPerson)
        list2.Add(t1)

        Dim linqresult = From p1 In list Join p2 In list2 On New With {Key p1.id, Key p1.name} Equals New With {Key p2.id, Key p2.name} Select p1.id, p1.name

    End Sub

我意识到我可以这样做：

 Dim list3 As New List(Of TestPerson)
        For Each var In test
            Dim tyPerson As New TestPerson
            tyPerson.id = var.id
            tyPerson.name = var.name
            list3.Add(tyPerson)
        Next

是否可以将.ToList与通用列表一起使用？

更新继Ed Ednketts的评论之后;我试过这个：

 Dim linqresult As List(Of TestPerson) = test.ToList

我得到的编译错误是：

Value of type 'System.Collections.Generic.List(Of <anonymous type>)' cannot be converted to 'System.Collections.Generic.List(Of com.Genie.PresentationLayer.Console.TestPerson)

我也试过这个：

   Dim linqresult = test.ToList
                For Each var As TestPerson In linqresult

                Next

我得到的错误是：

Value of type '<anonymous type> (line 36)' cannot be converted to 'com.Genie.PresentationLayer.Console.TestPerson

Answer 1

ToList不是你的问题。您正在生成匿名类型，并尝试将其存储在已知类型的列表中。

将Linq查询更改为投影到已知类型

Dim linqresult = From p1 In list _
                 Join p2 In list2 _
                   On New With {Key p1.id, Key p1.name} _
                   Equals New With {Key p2.id, Key p2.name} _
                   Select New TestPerson With {Id = p1.id, Name = p1.name}

或

Dim linqresult = From p1 In list _
                 Join p2 In list2 _
                   On New With {Key p1.id, Key p1.name} _
                   Equals New With {Key p2.id, Key p2.name} _
                   Select p1

如果您想要列表中的实际项而不是新项。

Enumerable.tolist返回一个通用列表

1 个答案: