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";

//lt.Selected = true;

//ddp.Items.Add(lt);