Copy Row Cell values from GridView to ListBox on button click in ASP.Net

Please refer this code

<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
    runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField DataField="Id" HeaderText="Id" ItemStyle-Width="30" />
        <asp:BoundField DataField="Name" HeaderText="Name" ItemStyle-Width="150" />
        <asp:BoundField DataField="Country" HeaderText="Country" ItemStyle-Width="150" />
    </Columns>
</asp:GridView>
<hr />
Select column
<asp:DropDownList ID="ddlColumns" runat="server">
</asp:DropDownList>
<br />
<asp:LinkButton Text="Show colums data in ListBox" OnClick="ShowColumnData" runat="server"></asp:LinkButton>
<br />
<asp:ListBox ID="lbColumns" runat="server"></asp:ListBox>

Namespace

using System.Data;

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id", typeof(int)),
                        new DataColumn("Name", typeof(string)),
                        new DataColumn("Country",typeof(string)) });
        dt.Rows.Add(1, "John Hammond", "United States");
        dt.Rows.Add(2, "Mudassar Khan", "India");
        dt.Rows.Add(3, "Suzanne Mathews", "France");
        dt.Rows.Add(4, "Robert Schidner", "Russia");
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
    for (int i = 0; i < this.GridView1.HeaderRow.Cells.Count; i++)
    {
        this.ddlColumns.Items.Add(new ListItem(this.GridView1.HeaderRow.Cells[i].Text, i.ToString()));
    }
}

protected void ShowColumnData(object sender, EventArgs e)
{
    int cellIndex = Convert.ToInt32(this.ddlColumns.SelectedItem.Value);
    foreach (GridViewRow row in this.GridView1.Rows)
    {
        this.lbColumns.Items.Add(new ListItem(row.Cells[cellIndex].Text));
    }
}

Screenshot