DataTable dt = Utility.Getrole();
DroList.DataSource = dt;
DroList.DataTextField = "description";
DroList.DataValueField = "name";
DroList.DataBind();
DroList.Items.Insert(0, new ListItem("请选择", "请选择"));
SetDropListDefaultStatus（DroList）

//触发事件
AutoPostBack设置为True，SelectedIndexChanged事件里写你需要做的代码

//下拉框缺省为空
public void SetDropListDefaultStatus(DropDownList list)
{
　　list.Items.Insert(0, new ListItem(String.Empty, String.Empty));
　　list.SelectedIndex = 0;
}

绑定下拉控件