How to keep DropDownList1 selected value after postback?
<p>I have two DropDownLists. Once a DropDownList1 value is selected, DropDownList2 will populate based on Dropdownlist1.</p>

<p>But after the page refreshes, the dropdownlist1 selected value is changed to the top-most value (the DropDownList is populate by a database).</p>

<p>.aspx:</p>

<pre><code>&lt;asp:DropDownList ID="DropDownList1" runat="server" Width="300px" CssClass="makeselect" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged" AutoPostBack="True" AppendDataBoundItems="true"&gt;
&lt;/asp:DropDownList&gt;
</code></pre>

<p>.cs:</p>

<pre><code>protected void Page_Load(object sender, EventArgs e) {      

    DataTable subjects = new DataTable();

    if (Page.IsPostBack == false) {
        using (SqlConnection con = new SqlConnection(constring)) {

            SqlDataAdapter adapter = new SqlDataAdapter("SELECT VehicleMake FROM VehicleDB", con);
            adapter.Fill(subjects);

            con.Open();

            DropDownList1.DataSource = subjects;
            DropDownList1.DataTextField = "VehicleMake";
            DropDownList1.DataValueField = "";
            DropDownList1.DataBind();

            con.Close();
        }
    }
}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e) {
    string makename = DropDownList1.SelectedItem.Value;
    keepname = makename;

    Response.Redirect("default.aspx?QSVehicleMake="+makename);
}
</code></pre>