ListItemCollection 类
列表控件中的 ListItem 对象的集合。无法继承此类。
**命名空间:**System.Web.UI.WebControls
**程序集:**System.Web（在 system.web.dll 中）
语法
声明
Public NotInheritable Class ListItemCollection
Implements IList, ICollection, IEnumerable, IStateManager
用法
Dim instance As ListItemCollection
public sealed class ListItemCollection : IList, ICollection, IEnumerable,
IStateManager
public ref class ListItemCollection sealed : IList, ICollection, IEnumerable,
IStateManager
public final class ListItemCollection implements IList, ICollection,
IEnumerable, IStateManager
public final class ListItemCollection implements IList, ICollection,
IEnumerable, IStateManager
备注
ListItemCollection 类表示 ListItem 对象的集合。ListItem 对象反过来表示显示在列表控件中的项，如 ListBox。若要以编程方式从列表控件中检索 ListItem 对象，请使用以下方法之一：
利用数组表示法使用索引器从集合中获取单个 ListItem。
使用 CopyTo 方法将集合的内容复制到 System.Array 对象，然后可以使用该对象获取集合中的项。
使用 GetEnumerator 方法创建一个实现了 System.Collections.IEnumerator 的对象，然后可以使用该对象从集合中获取项。
使用 foreach (C#) 或 For Each (Visual Basic) 循环访问集合。
Count 属性指定集合中项的总数，常用于确定集合的上限。通过使用 Add 和 Remove 方法，可以将项添加到该集合和从该集合中移除项。
示例
下面的代码示例演示如何创建 ListItemCollection 对象、将项添加到集合中以及从集合中移除项。该示例中，名为 listBoxData 的 ListItemCollection 用作名为 ListBox1 的 ListBox 控件的数据源，而名为 ddBoxData 的 ListItemCollection 则用作名为 DropDownList1 的 DropDownList 控件的数据源。
<%@ Page language="VB" AutoEventWireup="true" %>
<%@ Import Namespace="System.Data" %>
<HTML>
<HEAD>
<SCRIPT runat="server">
Private Sub Page_Load(sender As Object, e As System.EventArgs) Handles MyBase.Load
' If this isn't the first time the page is loaded in this session,
' then don't recreate the DataTables.
If Not IsPostBack Then
' Create a new ListItemCollection.
Dim listBoxData As New ListItemCollection()
' Add items to the collection.
listBoxData.Add(New ListItem("apples"))
listBoxData.Add(New ListItem("bananas"))
listBoxData.Add(New ListItem("cherries"))
listBoxData.Add("grapes")
listBoxData.Add("mangos")
listBoxData.Add("oranges")
' Set the ListItemCollection as the data source for ListBox1.
ListBox1.DataSource = listBoxData
ListBox1.DataBind()
' Create a new ListItemCollection.
Dim ddBoxData As New ListItemCollection()
' For now, just bind the data to the DropDownList.
DropDownList1.DataSource = ddBoxData
DropDownList1.DataBind()
End If
End Sub 'Page_Load
Private Sub moveButton1_Click(sender As Object, e As System.EventArgs)
'Set the SelectedIndex to -1 so no items are selected.
' The new item will be set as the selected item when it is added.
DropDownList1.SelectedIndex = - 1
' Add the selected item to DropDownList1.
DropDownList1.Items.Add(ListBox1.SelectedItem)
' Delete the selected item from ListBox1.
ListBox1.Items.Remove(ListBox1.SelectedItem)
End Sub 'moveButton1_Click
Private Sub moveButton2_Click(sender As Object, e As System.EventArgs)
'Set the SelectedIndex to -1 so no items are selected.
' The new item will be set as the selected item when it is added.
ListBox1.SelectedIndex = - 1
' Add the selected item to ListBox1.
ListBox1.Items.Add(DropDownList1.SelectedItem)
'Delete the selected item from DropDownList1.
DropDownList1.Items.Remove(DropDownList1.SelectedItem)
End Sub 'moveButton2_Click
</SCRIPT>
</HEAD>
<BODY>
<form runat="server">
<table cellpadding="6" border="0">
<tr>
<td rowspan="2" valign="top">
<asp:ListBox id="ListBox1" runat="server"
SelectionMode="Single" Width="100px">
</asp:ListBox>
</td>
<td>
<asp:Button id="moveButton1" runat="server" Text="Move -->"
Width="100px" OnClick="moveButton1_Click"></asp:Button>
</td>
<td rowspan="2" valign="top">
<asp:DropDownList Runat="server" ID="DropDownList1"
Width="100px">
</asp:DropDownList>
</td>
</tr>
<tr>
<td>
<asp:Button ID="moveButton2" Runat="server" Text="<-- Move"
Width="100px" onClick="moveButton2_Click"></asp:Button>
</td>
</tr>
</table>
</form>
</BODY>
</HTML>
<%@ Page language="C#" AutoEventWireup="true" %>
<%@ Import Namespace="System.Data" %>
<HTML>
<HEAD>
<SCRIPT runat="server">
private void Page_Load(object sender, System.EventArgs e)
{
// If this isn't the first time the page is loaded in this session,
// then don't recreate the DataTables.
if (!IsPostBack)
{
// Create a new ListItemCollection.
ListItemCollection listBoxData = new ListItemCollection();
// Add items to the collection.
listBoxData.Add(new ListItem("apples"));
listBoxData.Add(new ListItem("bananas"));
listBoxData.Add(new ListItem("cherries"));
listBoxData.Add("grapes");
listBoxData.Add("mangos");
listBoxData.Add("oranges");
// Set the ListItemCollection as the data source for ListBox1.
ListBox1.DataSource = listBoxData;
ListBox1.DataBind();
// Create a new ListItemCollection.
ListItemCollection ddBoxData = new ListItemCollection();
// For now, just bind the data to the DropDownList.
DropDownList1.DataSource = ddBoxData;
DropDownList1.DataBind();
}
}
private void moveButton1_Click(object sender, System.EventArgs e)
{
//Set the SelectedIndex to -1 so no items are selected.
// The new item will be set as the selected item when it is added.
DropDownList1.SelectedIndex = -1;
// Add the selected item to DropDownList1.
DropDownList1.Items.Add(ListBox1.SelectedItem);
// Delete the selected item from ListBox1.
ListBox1.Items.Remove(ListBox1.SelectedItem);
}
private void moveButton2_Click(object sender, System.EventArgs e)
{
//Set the SelectedIndex to -1 so no items are selected.
// The new item will be set as the selected item when it is added.
ListBox1.SelectedIndex = -1;
// Add the selected item to ListBox1.
ListBox1.Items.Add(DropDownList1.SelectedItem);
//Delete the selected item from DropDownList1.
DropDownList1.Items.Remove(DropDownList1.SelectedItem);
}
</SCRIPT>
</HEAD>
<BODY>
<form runat="server">
<table cellpadding="6" border="0">
<tr>
<td rowspan="2" valign="top">
<asp:ListBox id="ListBox1" runat="server"
SelectionMode="Single" Width="100px">
</asp:ListBox>
</td>
<td>
<asp:Button id="moveButton1" runat="server" Text="Move -->"
Width="100px" OnClick="moveButton1_Click"></asp:Button>
</td>
<td rowspan="2" valign="top">
<asp:DropDownList Runat="server" ID="DropDownList1"
Width="100px">
</asp:DropDownList>
</td>
</tr>
<tr>
<td>
<asp:Button ID="moveButton2" Runat="server" Text="<-- Move"
Width="100px" onClick="moveButton2_Click"></asp:Button>
</td>
</tr>
</table>
</form>
</BODY>
</HTML>
<!-- This example demonstrates how to select multiple items from a DataList
and add the selected items to a DataGrid. The example uses a For Each loop
to iterate through the ListItem objects in the ListItemCollection of ListBox1. -->
<!-- This example demonstrates how to select multiple items from a DataList and add the
selected items to a DataGrid. The example uses a foreach loop to iterate through
the ListItem objects in the ListItemCollection of ListBox1. -->
<%@ Page language="VB" AutoEventWireup="true"%>
<%@ Import Namespace="System.Data" %>
<HTML>
<HEAD>
<SCRIPT runat="server">
' Global Variables.
Private dv As DataView
Private dt As New DataTable()
Private Sub Page_Load(sender As Object, e As System.EventArgs)
' Set the number of rows displayed in the ListBox to be
' the number of items in the ListBoxCollection.
ListBox1.Rows = ListBox1.Items.Count
' If the DataTable is already stored in the Web form's default
' HttpSessionState variable, then don't recreate the DataTable.
If Session("data") Is Nothing Then
' Add columns to the DataTable.
dt.Columns.Add(New DataColumn("Item"))
dt.Columns.Add(New DataColumn("Price"))
' Store the DataTable in the Session variable so it can be
' accessed again later.
Session("data") = dt
' Use the table to create a DataView, because the DataGrid
' can only bind to a data source that implements IEnumerable.
dv = New DataView(dt)
' Set the DataView as the data source, and bind it to the DataGrid.
DataGrid1.DataSource = dv
DataGrid1.DataBind()
End If
End Sub
Private Sub addButton_Click(sender As Object, e As System.EventArgs)
' Add the items selected in ListBox1 to DataGrid1.
Dim item As ListItem
For Each item In ListBox1.Items
If item.Selected Then
' Add the item to the DataGrid.
' First, get the DataTable from the Session variable.
dt = CType(Session("data"), DataTable)
If Not (dt Is Nothing) Then
' Create a new DataRow in the DataTable.
Dim dr As DataRow
dr = dt.NewRow()
' Add the item to the new DataRow.
dr("Item") = item.Text
' Add the item's value to the DataRow.
dr("Price") = item.Value
' Add the DataRow to the DataTable.
dt.Rows.Add(dr)
' Rebind the data to DataGrid1.
dv = new DataView(dt)
DataGrid1.DataSource = dv
DataGrid1.DataBind()
End If
End If
Next item
End Sub
</SCRIPT>
</HEAD>
<BODY>
<form runat="server">
<h3> ListItemCollection Example </h3>
<table cellpadding="6" border="0">
<tr>
<td valign="top">
<asp:ListBox id="ListBox1" runat="server" SelectionMode="Multiple">
<asp:ListItem Value=".89">apples</asp:ListItem>
<asp:ListItem Value=".49">bananas</asp:ListItem>
<asp:ListItem Value="2.99">cherries</asp:ListItem>
<asp:ListItem Value="1.49">grapes</asp:ListItem>
<asp:ListItem Value="2.00">mangos</asp:ListItem>
<asp:ListItem Value="1.09">oranges</asp:ListItem>
</asp:ListBox>
</td>
<td valign="top">
<asp:Button id="addButton" runat="server" Text="Add -->"
Width="100px" OnClick="addButton_Click"></asp:Button>
</td>
<td valign="top">
<asp:DataGrid Runat="server" ID="DataGrid1" CellPadding="4">
</asp:DataGrid>
</td>
</tr>
</table>
</form>
</body>
</HTML>
<%@ Page language="c#" AutoEventWireup="true"%>
<%@ Import Namespace="System.Data" %>
<HTML>
<HEAD>
<SCRIPT language="C#" runat="server">
// Global Variables.
private DataView dv;
private DataTable dt = new DataTable();
private void Page_Load(object sender, System.EventArgs e)
{
// Set the number of rows displayed in the ListBox to be
// the number of items in the ListBoxCollection.
ListBox1.Rows = ListBox1.Items.Count;
// If the DataTable is already stored in the Web form's default
// HttpSessionState variable, then don't recreate the DataTable.
if (Session["data"] == null)
{
// Add columns to the DataTable.
dt.Columns.Add(new DataColumn("Item"));
dt.Columns.Add(new DataColumn("Price"));
// Store the DataTable in the Session variable so it can
// be accessed again later.
Session["data"] = dt;
// Use the table to create a DataView, because the DataGrid
// can only bind to a data source that implements IEnumerable.
dv = new DataView(dt);
// Set the DataView as the data source, and bind it to the DataGrid.
DataGrid1.DataSource = dv;
DataGrid1.DataBind();
}
}
private void addButton_Click(object sender, System.EventArgs e)
{
// Add the items selected in ListBox1 to DataGrid1.
foreach (ListItem item in ListBox1.Items)
{
if (item.Selected)
{
// Add the item to the DataGrid.
// First, get the DataTable from the Session variable.
dt = (DataTable)Session["data"];
if (dt != null)
{
// Create a new DataRow in the DataTable.
DataRow dr = dt.NewRow();
// Add the item to the new DataRow.
dr["Item"] = item.Text;
// Add the item's value to the DataRow.
dr["Price"] = item.Value;
// Add the DataRow to the DataTable.
dt.Rows.Add(dr);
// Rebind the data to DataGrid1.
dv = new DataView(dt);
DataGrid1.DataSource = dv;
DataGrid1.DataBind();
}
}
}
}
</SCRIPT>
</HEAD>
<BODY>
<form runat="server">
<h3> ListItemCollection Example </h3>
<table cellpadding="6" border="0">
<tr>
<td valign="top">
<asp:ListBox id="ListBox1" runat="server" SelectionMode="Multiple">
<asp:ListItem Value=".89">apples</asp:ListItem>
<asp:ListItem Value=".49">bananas</asp:ListItem>
<asp:ListItem Value="2.99">cherries</asp:ListItem>
<asp:ListItem Value="1.49">grapes</asp:ListItem>
<asp:ListItem Value="2.00">mangos</asp:ListItem>
<asp:ListItem Value="1.09">oranges</asp:ListItem>
</asp:ListBox>
</td>
<td valign="top">
<asp:Button id="addButton" runat="server" Text="Add -->"
Width="100px" OnClick="addButton_Click"></asp:Button>
</td>
<td valign="top">
<asp:DataGrid Runat="server" ID="DataGrid1" CellPadding="4">
</asp:DataGrid>
</td>
</tr>
</table>
</form>
</body>
</HTML>
继承层次结构
System.Object
System.Web.UI.WebControls.ListItemCollection
线程安全
此类型的任何公共静态（Visual Basic 中的 Shared）成员都是线程安全的，但不保证所有实例成员都是线程安全的。
平台
Windows 98、Windows 2000 SP4、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0
请参见
参考
ListItemCollection 成员
System.Web.UI.WebControls 命名空间
ListItem 类
ListBox 类
CopyTo
GetEnumerator
System.Collections.IEnumerator
Count
Add
Remove