How to select a value from a child form and send it to parent form?

page1
<asp:TextBox id="txtSelect" style="Z-INDEX: 101; LEFT: 186px; POSITION: absolute; TOP: 19px"
runat="server"></asp:TextBox>
<a href="javascript:my_window=window.open('page2.aspx ?formname=Form1.txtSelect','my_window','width=300, height=300');my_window.focus()">
Select CategoryName</a>

page2

<aspropDownList id="DropDownList1" style="Z-INDEX: 101; LEFT: 180px; POSITION: absolute; TOP: 66px"
runat="server" AutoPostBack="True">
<asp:Label id="Label1" style="Z-INDEX: 102; LEFT: 16px; POSITION: absolute; TOP: 66px" runat="server">Select Category Name
<asp:Literal id="Literal1" runat="server">


private void Page_Load(object sender, System.EventArgs e)
{
// Put user code to initialize the page here
if (!Page.IsPostBack )
{
//Fill DataSet
DropDownList1.DataSource = ds.Tables[0];
DropDownList1.DataTextField = "CategoryName";
DropDownList1.DataValueField = "CategoryId";
DropDownList1.DataBind();
}
}

private void DropDownList1_SelectedIndexChanged(object sender, System.EventArgs e)
{
try
{
string strjscript = @"<script language=""javascript"">";
strjscript = strjscript + "window.opener." + HttpContext.Current.Request.QueryString["formname"].ToString () + ".value = '" + DropDownList1.SelectedItem.Text + "';window.close();";
strjscript = strjscript + "</script>";
Literal1.Text = strjscript;
}
catch(Exception ex)
{
Response.Write (ex.Message );
}
}

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