Question

我完全不知道为什么linq抛出一个Unable来强制转换'System.Int32'类型的对象来输入'System.String'异常。该代码是泛型函数的一部分，用于将DataTextField和DataValueField从无类型DataTable中拉出，并将它们放在KeyValuePair（string，string）列表中。我为linq查询上方的每个循环添加了一个以逐步执行每个项目，并且工作正常。为DataValueField返回的数据是数字，但它在无类型集中。我在字段上尝试了ToString（），不知道接下来要尝试什么。任何帮助将不胜感激。

    Private Function GetCurrentBoundControlDT(ByVal StoredProcedure As String, ByVal ParamList As String, ByVal DataTextField As String, ByVal DataValueField As String) As List(Of KeyValuePair(Of String, String))
        Dim ds As DataSet = Nothing
        Dim dt As DataTable = Nothing
        Dim BoundControlDataList As List(Of KeyValuePair(Of String, String)) = Nothing

        If ParamList.Trim <> String.Empty Then
            StoredProcedure = String.Format("{0} {1}", StoredProcedure, ParamList)
        End If

        ds = RG.GetDS(StoredProcedure)

        If Not ds Is Nothing AndAlso ds.Tables.Count > 0 Then
            dt = ds.Tables(0)

            'This works fine
            For Each r As DataRow In dt.Rows
                Dim test1 As String = r(DataTextField)
                Dim test2 As String = r(DataValueField)
                Dim kv As New KeyValuePair(Of String, String)(test1, test2)
            Next
            'Blows up here...
            BoundControlDataList = (From ThisTable In dt.AsEnumerable() _
                    Select New KeyValuePair(Of String, String)(ThisTable.Field(Of String)(DataTextField).ToString(), _
                                               ThisTable.Field(Of String)(DataValueField).ToString())).ToList()
        End If

        Return BoundControlDataList
    End Function

Answer 1

管理解决问题。它不是很漂亮，但有效。似乎（字符串）不是一个演员而是建议。我猜（对象）应该正确处理任何原始数据，并在字段周围包装Convert.ToString（）。以下变化是它做了什么......

            BoundControlDataList = (From t In dt.AsEnumerable() _
                                    Select New KeyValuePair(Of String, String)(Convert.ToString(t.Field(Of Object)(DataTextField).ToString()), _
                                     Convert.ToString(t.Field(Of Object)(DataValueField).ToString()))).ToList()

Linq to Untyped Datatable中的对象无法将类型为'System.Int32'的对象强制转换为'System.String'类型

1 个答案: