How to dropdown value remain after refresh page

void BindState()
   {
       DCI_Assign_Inspectors_DetailsClient client = new DCI_Assign_Inspectors_DetailsClient();
       DataSet ds = new DataSet();
       Prop objprop = new Prop();
       client.Open();
       objprop.Mode = "1";
       objprop.StateCode = "";

       try
       {
           ds = client.BindState(objprop);

           if (ds.Tables[0].Rows.Count > 0)
           {
               DrpState.DataSource = ds;
               DrpState.DataTextField = "State_Name";
               DrpState.DataValueField = "State_Code";
               DrpState.DataBind();
               DrpState.Items.Insert(0, new ListItem("--Please Select--", "All"));
           }

       }
       catch (Exception ex)
       {
           ScriptManager.RegisterStartupScript(Page, Page.GetType(), "InvalidArgs", "alert(" + ex.Message + ");", true);

       }
       finally
       {
           ds.Dispose();
           client.Close();
           objprop = null;
       }
   }