自定义类继承自DataSet,引用后第二次再引用而保存里面的数据的问题

Public Class lid401data_fh_rftr : Inherits DataSet
'定义一数据结构类,为其他层提供统一的接口
Public Const table_name As String = "FH_rftr"
Public Const ID_field As String = "ID"
Public Const ZDID_field As String = "ZDID"
Public Const RFID_field As String = "RFID"
Public Const TRDS_field As String = "TRDS"
Public Const BFDS_field As String = "BFDS"
Private Function buildtable()
Dim mytable As New DataTable(table_name)
mytable.Columns.Add(ID_field, System.Type.GetType("System.String"))
mytable.Columns.Add(ZDID_field, System.Type.GetType("System.String"))
mytable.Columns.Add(RFID_field, System.Type.GetType("System.String"))
mytable.Columns.Add(TRDS_field, System.Type.GetType("System.String"))
mytable.Columns.Add(BFDS_field, System.Type.GetType("System.String"))
Tables.Add(mytable)
End Function
Public Sub lid401data_fh_rftr()
buildtable()
End Sub
End Class

第一次引用
Private Sub create_rftrnew()
'创建数据表
Dim zdtrdata As Common.lid401data_fh_rftr = New Common.lid401data_fh_rftr()

Dim mytb As DataTable = zdtrdata.Tables(zdtrdata.table_name)
zdtrdata.lid401data_fh_rftr()
Dim row As DataRow = mytb.NewRow
'读取页面控件数据填充数据表
row(zdtrdata.TRDS_field) = Trim(TextBox_trds.Text)
row(zdtrdata.BFDS_field) = Trim(TextBox_bfds.Text)

mytb.Rows.Add(row)
DataGrid1.DataSource = zdtrdata
End Sub

然后我第二次引用应该怎么引用法,而不让第一次的数据丢失而是在原来的基本上再加上一行?
我是没提交到数据库的