如何遍历Calendar控件内的子控件

我给日历控件里面的每个日期下面增加了个下拉框给用户选择
 protected void ShiftDateCalendar_DayRender(object sender, DayRenderEventArgs e)
    {
        if (e.Day.IsOtherMonth)
        {
            e.Cell.Controls.Clear();
        }
        if (e.Day.Date > DateTime.Now && !e.Day.IsOtherMonth)
        {
            DropDownList ddl = new DropDownList();
            ddl.ID = "ddlShifts";
            if (ViewState["myds"] != null)
            {
                ddl.DataSource = (DataSet)ViewState["myds"];
                ddl.DataTextField = "ShiftCode";
                ddl.DataValueField = "ShiftCode";
                ddl.DataBind();
            }
            ListItem item = new ListItem("休息", "");
            ddl.Items.Add(item);            e.Cell.Controls.Add(new LiteralControl("<br/>"));
            e.Cell.Controls.Add(ddl);
        }    }现在想获取这些下拉框对应的日期及选择内容，然后批量保存到数据库。怎么遍历Calendar控件内的子控件获取呢？