สร้างปุ่ม imagebutton ขึ้น แล้วต้องการให้ client คลิก ลิ้งไปอีกไฟล์

<asp:TextBox ID="txtPur_id" runat="server"></asp:TextBox>
                    <asp:ImageButton ID="btnpurid" runat="server" Height="22px" ImageUrl="~/Select-Button.gif" Width="28px" OnClientClick="window.open('PurchaseRec.aspx')" /></td>

Protected Sub txtPur_id_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtPur_id.TextChanged
        Dim idx As String = Request.QueryString("Pur_id")
        txtPur_id.Text = idx
        Dim sql As String = "SELECT Tl_Purchase.St_id, Tl_Stock.St_name, Tl_Purchase.Pur_amount ,Tl_Purchase.Pur_id FROM   Tl_Purchase INNER JOIN  Tl_Stock ON Tl_Purchase.St_id = Tl_Stock.St_Id WHERE Tl_Purchase.Pur_id ='" & txtPur_id.Text & "'"
        'Dim purid As String = DDLPurid.SelectedValue
        'Response.Write(purid)
        'Response.End()
        Dim mycommand As New SqlCommand(sql, Conn)
        Conn.Open()
        Dim mydatareader As SqlDataReader = mycommand.ExecuteReader()
        Dim found As Boolean = False
        While mydatareader.Read()
            found = True
        End While
        Conn.Close()
        If found = True Then
            txtPur_id.Enabled = False
            Showitempurchase()
        End If
    End Sub
 Sub Showitempurchase()
        'แสดงรายการของสินค้าให้เลือก
        DGRecieve.Visible = True
        Dim AdapterStock As New SqlDataAdapter("SELECT Tl_Purchase.St_id, Tl_Stock.St_name, Tl_Purchase.Pur_amount ,Tl_Purchase.Pur_id FROM   Tl_Purchase INNER JOIN  Tl_Stock ON Tl_Purchase.St_id = Tl_Stock.St_Id WHERE Tl_Purchase.Pur_id ='" & txtPur_id.Text & "'", Conn)
        'Response.Write(AdapterStock)
        'Response.End()
        AdapterStock.Fill(Ds, "DataPurchase")
        DGRecieve.DataSource = Ds.Tables("DataPurchase")
        DGRecieve.DataKeyField = "St_id"
        DGRecieve.DataBind()
    End Sub