【IT168 技术文档】在ASP.NET 2.0中，可以在数据绑定时，通过设置DropDownList的AppendDataBoundItems属性为true,在数据绑定之前添加一个新的项目，并且这个新加的项目会保存在ViewState之中。下面就是一个实现的例子：
<%@ Page Language="VB" AutoEventWireup="true" %><%@ Import Namespace =Namespace="System.Data" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><script runat="server"> Protected Sub Button1_Click()Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Response.Write("<li>DropDownList1 您选择的项目：" + DropDownList1.SelectedValue + _ " ; " + DropDownList1.SelectedItem.Text) Response.Write("<li>DropDownList2 您选择的项目：" + DropDownList2.SelectedValue + _ " ; " + DropDownList2.SelectedItem.Text) End Sub Protected Sub Page_Load()Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) If Not IsPostBack Then DropDownList1.AppendDataBoundItems = True DropDownList1.Items.Add(New ListItem("-- 请选择一个选择项 --", "")) DropDownList2.DataSource = CreateDataSource() DropDownList1.DataSource = CreateDataSource() DropDownList2.DataTextField = "text" DropDownList1.DataTextField = "text" DropDownList2.DataValueField = "id" DropDownList1.DataValueField = "id" DropDownList1.DataBind() DropDownList2.DataBind() End If End Sub Function CreateDataSource()Function CreateDataSource() As ICollection Dim dt As DataTable = New DataTable() Dim dr As DataRow dt.Columns.Add(New DataColumn("id", GetType(System.Int32))) dt.Columns.Add(New DataColumn("text", GetType(String))) For i As Integer = 0 To 6 dr = dt.NewRow() dr(0) = i dr(1) = "列表项目 " + i.ToString() dt.Rows.Add(dr) Next Dim dv As DataView = New DataView(dt) Return dv End Function</script><html xmlns="http://www.w3.org/1999/xhtml"><head id="Head1" runat="server"> <title>DropDownList 补充例子</title></head><body> <form id="form1" runat="server"> <asp:DropDownList ID="DropDownList1" runat="server"> </asp:DropDownList> <asp:DropDownList ID="DropDownList2" runat="server" AppendDataBoundItems="true"> <asp:ListItem Text="请选择" Value=""></asp:ListItem> </asp:DropDownList> <asp:Button ID="Button1" runat="server" Text="得到选择的值" OnClick="Button1_Click" /> </form></body></html> 
