使用Linq表达式键入预期错误

Question

我正在尝试在VB.net中编写一个linq查询，该查询按字符串对自定义对象列表进行分组并对数量进行求和。我一直在使用101 Linq示例，但在尝试处理集合时遇到了Type Expected错误。

这是我的Linq查询：

Dim summedAndGrouped = From s As GLLine In _ListOfGLLines
                       Group s By s.SEDOL Into grouped = Group
                       Select SEDOL, TotalIncome = grouped.Sum(Function(s) s.Income)

改编自Linq 101样本：http://msdn.microsoft.com/en-us/vstudio/bb737904#sumgroup

我非常感谢任何建议。下面是我的测试项目，我正在尝试解决这个问题：

Imports System.Text
Imports Microsoft.VisualStudio.TestTools.UnitTesting

<TestClass()>
Public Class UnitTest1

    Private _ListOfGLLines As New List(Of GLLine)

    <TestInitialize()>
        Public Sub Setup()
        SetupGLLinesCollection()
    End Sub

    <TestMethod()>
    Public Sub TestMethod1()
        Dim summedAndGrouped = From s As GLLine In _ListOfGLLines
                               Group s By s.SEDOL Into grouped = Group
                               Select SEDOL, TotalIncome = grouped.Sum(Function(s)    s.Income)

        Assert.AreEqual(summedAndGrouped.Count, 3)
    End Sub

    Public Sub SetupGLLinesCollection()
        _ListOfGLLines.Add(New GLLine("Bob1", 20, 10, 4, 6))
        _ListOfGLLines.Add(New GLLine("Bob1", 20, 10, 4, 6))
        _ListOfGLLines.Add(New GLLine("Bob2", 20, 10, 4, 6))
        _ListOfGLLines.Add(New GLLine("Bob2", 20, 10, 4, 6))
        _ListOfGLLines.Add(New GLLine("Bob3", 20, 10, 4, 6))
        _ListOfGLLines.Add(New GLLine("Bob3", 20, 10, 4, 6))
    End Sub

End Class

Public Class GLLine
    Public Property SEDOL As String
    Public Property Income As Decimal
    Public Property PID As Decimal
    Public Property Interest As Decimal
    Public Property Dividend As Decimal

    Public Sub New(SEDOL, Income, PID, Interest, Dividend)
        _SEDOL = SEDOL
        _Income = Income
        _PID = PID
        _Interest = Interest
        _Dividend = Dividend
    End Sub
End Class

编辑：看起来这个查询评估很好，我的混淆是因为当我将鼠标悬停在summedAndGrouped变量上时它给出了Type Expected错误，我认为是由于编译器需要先推断迭代器的类型它可以评估查询。我仍然希望确认为什么会发生这种情况以及如何避免它。