How to retain selected value of dropdownlist inside repeater controls after postback?

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ASP.NET

I have used two dropdown list inside repeater control of asp.net. I want to retain selected value of drop down which i selected before postback of the page.Please suggest what would be solution.



I have used this code inside itemdatabound events of repeter controls.

my code below:-

What should be add in this event to retaining the selected value after posting the page of dropdown list inside repeater contorols.

 protected void rptCustomers_ItemDataBound(object sender, RepeaterItemEventArgs e)
    {
                        DropDownList drplist = e.Item.FindControl("drpList") as DropDownList;
                        DropDownList drpSublist = e.Item.FindControl("drpSubcategory") as DropDownList;
 cmd.CommandType = CommandType.Text;
                        con.Open();
                        SqlDataReader idr = cmd.ExecuteReader();
                        DataTable dtcat = new DataTable();

                        dtcat.Load(idr);
                        if (dtcat.Rows.Count > 0)
                        {       
                            drplist.DataSource = dtcat;
                            drplist.DataValueField = "description";
                            drplist.DataTextField = "description";
                            drplist.DataBind();
                            idr.Close();
                            con.Close();
                        }    


 SqlDataReader idr2 = cmd.ExecuteReader();
                        DataTable dtcat2 = new DataTable();
                        dtcat2.Load(idr2);
                        if (dtcat.Rows.Count > 0)
                        {
                            drpSublist.DataSource = dtcat2;
                            drpSublist.DataValueField = "description";
                            drpSublist.DataTextField = "description";
                            drpSublist.DataBind();
                            idr.Close();
                            con.Close();
                        }
}

please suggest some solution of retaing selected value of dropdown list inside repeter after postback.

Thanks and regard.