dropdownlist的动态绑定数据然后怎么添加默认项“请选择”或空值

有两种方法：一种是用dual表查空值，然后绑定。另一种是先动态绑定数据后，然后插入一列默认项。 eg1: string selectQuery = select null extattrid,null extattrname from dual union all select extattrid,extattrname from VExtAttrDetail where extattrsn in (22); DataSet ds=dboperReq.GetDSet(selectQuery); ddlTrantype.DataTextField = extattrname; ddlTrantype.DataValueField=extattrid; ddlTrantype.DataSource=ds.Tables[0].DefaultView; ddlTrantype.DataBind();eg2: string selectQuery = select extattrid,extattrname from VExtAttrDetail where extattrsn in (22); DataSet ds=dboperReq.GetDSet(selectQuery); ddlTrantype.DataTextField = extattrname; ddlTrantype.DataValueField=extattrid; ddlTrantype.DataSource=ds.Tables[0].DefaultView; ddlTrantype.DataBind(); ddlTrantype.Items.Insert(0,new ListItem( , ));//或者ListItem it = new ListItem(请选择, 0); //mydroplist.Items.Insert(0,it);或者ListItem lt = new ListItem(); //lt.Text = 请选择;//lt.Value = 00;