How to add selected Value from GridView to DropDownList in ASP.Net

This way,

HTML:

<form id="form1" runat="server">
    <cc1:ToolkitScriptManager runat="server">
    </cc1:ToolkitScriptManager>
    <div>
        <asp:DropDownList ID="ddlNames" runat="server">
        </asp:DropDownList>
        <asp:Button ID="btnClick" runat="server" Text="Click Me" />
        <asp:Panel runat="server" ID="panel1" CssClass="modalPopup" align="center">
            <asp:GridView ID="gvNames" runat="server" AutoGenerateColumns="false">
                <Columns>
                    <asp:BoundField DataField="Name" HeaderText="Name" />
                    <asp:TemplateField>
                        <ItemTemplate>
                            <asp:Button ID="btnSelectName" runat="server" Text="Select" OnClick="SelectValue" />
                        </ItemTemplate>
                    </asp:TemplateField>
                </Columns>
            </asp:GridView>
            <asp:Button ID="btnCancel" runat="server" Text="Cancel" />
        </asp:Panel>
        <cc1:ModalPopupExtender BackgroundCssClass="modalBackground" runat="server" ID="mpeShow"
            TargetControlID="btnClick" PopupControlID="panel1" CancelControlID="btncancel">
        </cc1:ModalPopupExtender>
    </div>
    </form>

C#:

protected void Page_Load(object sender, EventArgs e)
        {
            if (!this.IsPostBack)
            {
                this.PopulateGrid();
            }
        }

        private void PopulateGrid()
        {
            DataTable dt = new DataTable();
            dt.Columns.AddRange(new DataColumn[1] { new DataColumn("Name", typeof(string)) });
            dt.Rows.Add("John");
            dt.Rows.Add("Jack");
            dt.Rows.Add("Micheal");
            dt.Rows.Add("Mike");
            dt.Rows.Add("Drak");
            this.gvNames.DataSource = dt;
            this.gvNames.DataBind();
        }

        protected void SelectValue(object sender, EventArgs e)
        {
            GridViewRow row = ((sender as Button).NamingContainer as GridViewRow);
            this.ddlNames.Items.Add(new ListItem(row.Cells[0].Text, row.Cells[0].Text));
        }

STYLE:

<style type="text/css">
        .modalBackground
        {
            background-color: Black;
            filter: alpha(opacity=40);
            opacity: 0.4;
        }
        .modalPopup
        {
            background-color: #FFFFFF;
            width: 300px;
            border: 3px solid #0DA9D0;
        }
    </style>