dropdownlist的动态绑定数据然后怎么添加默认项“请选择”以及如何清空成“请选择”

- 日理万妓 2022-09-21 04:51 123阅读 0赞

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); 红色是关键代码，那么如何选择请选择呢？也是两种方式，我比较倾向于后一种方式： 
     
      
       
      Default.aspx
     
      1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Web; 5 using System.Web.UI; 6 using System.Web.UI.WebControls; 7 
     8 namespace Wolfy.DropDownListDemo 9 { 10     public partial class Default : System.Web.UI.Page 11 { 12         protected void Page_Load(object sender, EventArgs e) 13 { 14             DropDownListProvince.DataSource = GetList(); 15             DropDownListProvince.DataTextField = "Name"; 16             DropDownListProvince.DataValueField = "ID"; 17 DropDownListProvince.DataBind(); 18             RepeaterList.DataSource = GetList(); 19 RepeaterList.DataBind(); 20 } 21         protected List<Province> GetList() 22 { 23             List<Province> list = new List<Province>(); 24             list.Add(new Province() { ID = 1, Name = "北京", Pid = 0 }); 25             list.Add(new Province() { ID = 2, Name = "上海", Pid = 0 }); 26             list.Add(new Province() { ID = 3, Name = "河南", Pid = 0 }); 27             list.Add(new Province() { ID = 4, Name = "河北", Pid = 0 }); 28             list.Add(new Province() { ID = 5, Name = "湖南", Pid = 0 }); 29             list.Add(new Province() { ID = 6, Name = "湖北", Pid = 0 }); 30             return list; 31 } 32 
    33         protected void LinkUpdate_Click(object sender, EventArgs e) 34 { 35             LinkButton link = sender as LinkButton; 36             if (link != null) 37 { 38                 int id = Convert.ToInt32(link.CommandArgument); 39                 Province pro = GetList().Find(a => a.ID == id); 40                 this.LiteralID.Text = pro.ID.ToString(); 41                 this.LiteralLevel.Text = pro.Pid.ToString(); 42                 //DropDownList的index是从零开始的 而绑定的数据的ID是从1开始的，所以为了对应需减一 43                 //改变默认选中项
    44                 this.DropDownListProvince.SelectedIndex = pro.ID-1; 45 } 46 } 47 } 48 } 方式二 1         protected void LinkUpdate_Click(object sender, EventArgs e) 2 { 3             LinkButton link = sender as LinkButton; 4             if (link != null) 5 { 6                 int id = Convert.ToInt32(link.CommandArgument); 7                 Province pro = GetList().Find(a => a.ID == id); 8                 this.LiteralID.Text = pro.ID.ToString(); 9                 this.LiteralLevel.Text = pro.Pid.ToString(); 10                 //方式二
    11                 ListItem item = DropDownListProvince.Items.FindByText(pro.Name);
    12                 if (item != null)
    13                 {
    14                     //防止出现多选的情况，将选中项 清除
    15                     DropDownListProvince.ClearSelection();
    16                     item.Selected = true;
    17                 }
    18             }
    19         }