datagrid无法编辑更新列值

  小弟初学，套用的书上的源代码改成我部门自用，在此部分代码中，更新datagrid中的数据innumstr值，不论怎么更改，该值都保持不变，望高手指教。
Sub Grid1_Update(ByVal Sender As Object, ByVal E As DataGridCommandEventArgs)

        Dim PaperCodeStr As String = E.Item.Cells(10).Text
        Dim InNumStr As String = CType(E.Item.Cells(8).Controls(0), TextBox).Text
        Dim CodeStr As String = E.Item.Cells(0).Text
        Dim sql As String
        If IsNumeric(InNumStr) Then
            Cnn = New SqlConnection(ConfigurationSettings.AppSettings("connection"))
            Cnn.Open()
            sql = "update paperinstoresheet set instorenum=" & CInt(InNumStr) & " where code='" & CodeStr & "' and papercode='" & PaperCodeStr & "'"         
            cmd = New SqlCommand(sql, Cnn)
            cmd.ExecuteNonQuery()
            Cnn.Close()
        End If
        DataGrid1.EditItemIndex = -1
        BindGrid()


    End Sub