不能在DropDownList 中选择多个项

在绑定DropDownList时如果出现多次绑定，会出错以下错误：

“不能在DropDownList 中选择多个项”

经了解，只需要在选中值是清空选择即可：xxDropDownList.ClearSelection() ；

/// <summary>
    /// 设定选中项
    /// </summary>
    /// <param name="list"></param>
    public static void SetListControl(ListControl list, string selectedValues)
    {
        if (string.IsNullOrEmpty(selectedValues))
            return;
        list.ClearSelection();
        foreach (string var in selectedValues.Split(','))
        {
            string value = var.Trim();
            if (value.Length > 0)
            {
                foreach (ListItem item in list.Items)
                {
                    if (item.Value == value)
                    {
                        item.Selected = true;
                        break;
                    }
                }
            }
        }
    }