设置DropDownList默认选中值

string called = Request.QueryString["Called"].ToString();
if (called != "" && called != null && called != "undefined")
{
        ListItem li = null;
        li = ddlHotPhoneNo.Items.FindByText(called);
        if (li != null)
        {
               int index = ddlHotPhoneNo.Items.IndexOf(li);
               ddlHotPhoneNo.SelectedIndex = index;
        }
}