window.opener.document.getelementbyid vb.net มันไม่ส่งค่ากลับมาอะค่ะ

<script type="text/javascript">
function OpenPopup() {
    window.open("PurchaseRec.aspx","List","scrollbars=no,resizable=no,width=500,height=400");
    return false;
}
</script>

<script language="javascript">
function GetRowValue(val)
{
    // hardcoded value used to minimize the code.
    // ControlID can instead be passed as query string to the popup window
    window.opener.document.getElementById("txtPur_id").value = val;
    window.close();
}
</script>

Imports System.Data
Imports System.Data.SqlClient
Partial Public Class PurchaseRec
    Inherits System.Web.UI.Page
    Dim ConnStr As String = "server=(local);database=DB_CMS;uid=AdminCMS;password=qaz123"
    Dim Conn As New SqlConnection(ConnStr)
    Dim Myda As New SqlDataAdapter("Select * From Tl_Stock", Conn)
    Dim CmdStock, CmdCompany, CmdBuy, Cmdrecieve As SqlCommand
    Dim Ds As New DataSet
    Dim sql As String
    Dim Cmd As SqlCommand
    Dim Ad As SqlDataAdapter
    Dim dview As DataView

    Sub showdatagrid()
        sql = "SELECT Tl_Purchase.St_id, Tl_Stock.St_name,Tl_Stock.St_Price, Tl_Purchase.Pur_amount ,Tl_Purchase.Pur_id FROM   Tl_Purchase INNER JOIN  Tl_Stock ON Tl_Purchase.St_id = Tl_Stock.St_Id order by Tl_Purchase.Pur_id "
        '//กำหนด Sqlสำหรับอ่านข้อมูล
        Ad = New SqlDataAdapter(Sql, Conn) '///ประมวลผลคำสั่งอ่านข้อมูล
        Ad.Fill(Ds, "Table1") '///นำข้อมูลที่อ่านข้อมูลได้ไปให้กับDsแบบดาต้าเซต
        dview = Ds.Tables("Table1").DefaultView '///นำข้อมูลในDsแบบดาต้าเซตไปให้ดาต้าวิว
        sql = "SELECT Tl_Purchase.St_id, Tl_Stock.St_name,Tl_Stock.St_Price, Tl_Purchase.Pur_amount ,Tl_Purchase.Pur_id FROM   Tl_Purchase INNER JOIN  Tl_Stock ON Tl_Purchase.St_id = Tl_Stock.St_Id order by Tl_Purchase.Pur_id"
        Ad = New SqlDataAdapter(sql, Conn)
        Ad.Fill(Ds, "MyData")
        GridView1.DataSource = Ds.Tables("MyData")
        GridView1.DataBind()
        BtnCloseDisplay.Visible = True

    End Sub
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        showdatagrid()

    End Sub

    Protected Sub BtnCloseDisplay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnCloseDisplay.Click
        Response.Redirect("Add_Recieve.aspx")
    End Sub

    Private Sub GridView1_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles GridView1.RowDataBound
        If (e.Row.RowType = DataControlRowType.DataRow) Then
            'assuming that the required value column is the second column in gridview
            DirectCast(e.Row.FindControl("LinkButton2"), LinkButton).Attributes.Add("onclick", "javascript:GetRowValue('" & e.Row.Cells(0).Text & "')")
        End If
    End Sub
End Class