用Javascript为DropDownList控件下拉式选择添加一个Item至定义索引位置。

准备数据，创建一个对象，将是存储DropDownList控件每个Item数据。

复制代码 代码如下:

Imports Microsoft.VisualBasic

Namespace Insus.NET

Public Class Catalog

Private _ID As Integer

Private _Name As String

Public Property ID As Integer

Get

Return _ID

End Get

Set(value As Integer)

_ID = value

End Set

End Property

Public Property Name As String

Get

Return _Name

End Get

Set(value As String)

_Name = value

End Set

End Property

End Class

End Namespace

在.aspx放置一个DropDownList控件：

复制代码 代码如下:

<asp:DropDownList ID="DropDownListCatalog" runat="server"></asp:DropDownList>

在.aspx.vb绑定数据：

复制代码 代码如下:

Imports Insus.NET

Partial Class _Default

Inherits System.Web.UI.Page

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load

If Not IsPostBack Then

Data_Binding()

End If

End Sub

Private Sub Data_Binding()

Me.DropDownListCatalog.DataSource = GetData()

Me.DropDownListCatalog.DataValueField = "ID"

Me.DropDownListCatalog.DataTextField = "Name"

Me.DropDownListCatalog.DataBind()

End Sub

Private Function GetData() As List(Of Catalog)

Dim cls As New List(Of Catalog)

Dim cl As Catalog = New Catalog()

cl.ID = 1

cl.Name = "新闻频道"

cls.Add(cl)

cl = New Catalog()

cl.ID = 2

cl.Name = "体育频道"

cls.Add(cl)

cl = New Catalog()

cl.ID = 3

cl.Name = "军事频道"

cls.Add(cl)

cl = New Catalog()

cl.ID = 4

cl.Name = "教育频道"

cls.Add(cl)

Return cls

End Function

End Class

准备数据与环境后，写Javascript:

复制代码 代码如下:

window.onload = function () {

var catalog = document.getElementById("<%=DropDownListCatalog.ClientID%>");

var obj = document.createElement("option")

obj.text = "请选择..."

obj.value = 0

catalog.options.insertBefore(obj, catalog.options[0]);

}

DEMO: