ASP.Net 错误 - 无法转换类型为“System.String”的对象输入“System.Data.DataTable”

Question

我收到以下错误

无法将“System.String”类型的对象转换为“System.Data.DataTable”类型。

这是我使用的代码

Dim str As String = String.Empty

    If (Session("Brief") IsNot Nothing) Then

        Dim dt As DataTable = Session("Brief")
        If (dt.Rows.Count > 0) Then
            For Each dr As DataRow In dt.Rows
                If (str.Length > 0) Then str += ","
                str += dr("talentID").ToString()
            Next
        End If

    End If

    Return str

谢谢

Answer 1

我不是 VB 人员，但我认为您需要将会话变量转换为正确的类型（DataTable）：

Dim dt As DataTable = CType(Session("Brief"), DataTable);

Answer 2

我认为您需要“投射”Session(“Brief”)：

Dim dt As DataTable = CType(Session("Brief"), Datatable)

参见示例 此处

Answer 3

这个怎么样：

Dim str As String = ""

If Not Session("Brief") Is Nothing Then
  Dim dt As DataTable = TryCast(Session("Brief"), DataTable)

  If Not dt Is Nothing AndAlso dt.Rows.Count > 0 Then
    For Each dr As DataRow In dt.Rows
      If (str.Length > 0) Then
        str += ","
      End If

      str += dr("talentID").ToString()
    Next
  End If
End If

Return str

使用 TryCast 并检查强制转换是否成功...

下面的版本添加了一些 LINQ 以进行良好的测量：

Dim str As String = ""

If Not Session("Brief") Is Nothing Then
  Dim dt As DataTable = TryCast(Session("Brief"), DataTable)

  If Not dt Is Nothing AndAlso dt.Rows.Count > 0 Then
    str = Join((From r In dt Select CStr(r("talentID"))).ToArray, ",")
  End If
End If

Return str