我无法在gridview的第一行添加下拉列表

我添加了gridview，它与存储在会话变量中的csv文件数据绑定:

 dgData.DataSource = Session["csvdata"];
 dgData.DataBind();

它能完美结合。但我需要添加下拉列表在gridview的第一行数据库列名与网格标题的映射。我使用这个代码来添加下拉列表。但是下拉菜单被添加到页眉而不是第一行。

 protected void dgData_RowCreated(object sender, GridViewRowEventArgs e)
{
      if (e.Row.RowType == DataControlRowType.Header )
    {
        for (Int32 i = 0; i < e.Row.Cells.Count; i++)
        {
            DropDownList ddl = new DropDownList();
            ddl.ID = "ddlCol" + i.ToString ();
            e.Row.Cells[i].Controls.Add(ddl);
        }
    }
}

 protected void dgData_RowDataBound(object sender, GridViewRowEventArgs e)
 {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            DropDownList ddl;
            if (e.Row.RowIndex == 0)
            {
                for (Int32 i = 0; i < e.Row.Cells.Count; i++)
                {
                    ddl = new DropDownList();
                    ddl.ID = "ddlCol" + i.ToString ();
                    e.Row.Cells[i].Controls.Add(ddl);
                }
            }
       }
}