Linq to Untyped Datatable中的對象無法將類型爲'System.Int32'的對象轉換爲鍵入'System.String'

Question

我完全不知道爲什麼linq會拋出一個「System.Int32」鍵入'System.String'異常。該代碼是通用函數的一部分，用於將DataTextField和DataValueField從無類型的DataTable中提取出來，並將它們放在KeyValuePair（string，string）的列表中。我爲linq查詢上的每個循環添加了一個遍歷每個項目的代碼，並且工作正常。爲DataValueField返回的數據是數字，但是它是在一個無類型的集合中。我在字段上嘗試了ToString（），不確定接下來要嘗試什麼。任何幫助，將不勝感激。

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

管理弄清楚。這不完全漂亮，但工程。似乎（字符串）並不像一個建議。我猜（對象）應該正確處理任何原始數據，並且圍繞該字段包裝Convert.ToString（）。以下變化是什麼...

  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()