Bind dropdownlist in gridview at run time

add one dropdownlist in templatefield
<asp:TemplateField>
<HeaderTemplate>Emp</HeaderTemplate>
<ItemTemplate ><asp:DropDownList ID="ddlStudent" runat ="server" OnLoad ="ddlStudent_load"></asp:DropDownList></ItemTemplate>
</asp:TemplateField>

Code is:
protected void ddlStudent_load(object sender, EventArgs e)
{
SqlDataAdapter da = new SqlDataAdapter("select sname,sno from student", cn);
DataTable dt = new DataTable();
da.Fill(dt);
DropDownList ddl = (DropDownList)sender;
ddl.DataSource = dt;
ddl.DataTextField = "sname";
ddl.DataValueField = "sno";
ddl.DataBind();
}