Dropdownlist有关问题?

Dropdownlist问题??在线等
Dropdownlist1.DataSource   =   ds;
                Dropdownlist1.DataTextField   =   "province ";
                Dropdownlist1.DataValueField   =   "leter ";
                Dropdownlist1.DataBind();

  我帮定以后默认是第一条怎么能让它默认为空就是不选中状态

------解决方案--------------------------------------------------------
再加一个item，Index设置为-1，程序取值的时候判断一下

------解决方案--------------------------------------------------------
ListItem itemNull = new ListItem();
itemNull.Text = string.Empty;
itemNull.Index = -1;

ddl.Items.Add(itemNull);
------解决方案--------------------------------------------------------
ListItem itemNull = new ListItem();
itemNull.Text = string.Empty;
itemNull.Value = -1;

ddl.Items.Add(itemNull);

应该是这样，sorry

------解决方案--------------------------------------------------------
ddl.Items.Insert(0,new ListItem( " ", "-1 "));
------解决方案--------------------------------------------------------
都行
------解决方案--------------------------------------------------------
Dropdownlist1.Item.add(new Item( "... ", "-1 "));


Dropdownlist1.DataSource = ds;

Dropdownlist1.DataTextField = "province ";
Dropdownlist1.DataValueField = "leter ";
Dropdownlist1.DataBind();


------解决方案--------------------------------------------------------
ListItem itemNull = new ListItem();
itemNull.Text = "请选择... ";
itemNull.Index = -1;

ddl.Items.Add(itemNull);

------解决方案--------------------------------------------------------
一般这样比较好
ddl.Items.Insert(0,new ListItem( "请选择 ", "-1 "));