ListControl.SelectedIndex Property (System.Web.UI.WebControls)

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Lightweight
ScriptFree
.NET Framework Class Library
ListControl.SelectedIndex Property

Gets or sets the lowest ordinal index of the selected items in the list.

Namespace:  System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)
Syntax
Visual Basic
<ThemeableAttribute(False)> _
<BindableAttribute(True)> _
<BrowsableAttribute(False)> _
Public Overridable Property SelectedIndex As Integer
C#
[ThemeableAttribute(false)]
[BindableAttribute(true)]
[BrowsableAttribute(false)]
public virtual int SelectedIndex { get; set; }
Visual C++
[ThemeableAttribute(false)]
[BindableAttribute(true)]
[BrowsableAttribute(false)]
public:
virtual property int SelectedIndex {
	int get ();
	void set (int value);
}
F#
[<ThemeableAttribute(false)>]
[<BindableAttribute(true)>]
[<BrowsableAttribute(false)>]
abstract SelectedIndex : int with get, set
[<ThemeableAttribute(false)>]
[<BindableAttribute(true)>]
[<BrowsableAttribute(false)>]
override SelectedIndex : int with get, set
ASP.NET
<asp:ListControl SelectedIndex="Int32" />

Property Value

Type: System.Int32
The lowest ordinal index of the selected items in the list. The default is -1, which indicates that nothing is selected.
Exceptions
Exception Condition
ArgumentOutOfRangeException

The index was set to less than -1, or greater than or equal to the number of items on the list at the time the list is rendered.

Remarks

Use this property to determine the index of the currently selected item in the list if the list control allows only one selection. If the list control supports multiple selections, use this property to determine the lowest index of the selected items.

The value of the SelectedIndex property is not specifically saved on postback. It is restored on postback using the SelectedValue property. For example, if the SelectedValue property is 4, on postback, the SelectedIndex property is set to the index of the ListItem object that has a Value property of 4. If more than one ListItem object has a Value property of 4, the first item in the Items collection is selected.

This property cannot be set by themes or style sheet themes. For more information, see ThemeableAttribute and ASP.NET Themes and Skins.

Examples

The following example demonstrates how to use SelectedIndex to determine the lowest index of the selected items in the CheckBoxList.

Visual Basic

<%@ Page Language="VB" AutoEventWireup="True" %>
<%@ Import Namespace="System.Data" %>

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
 <script language="vb" runat="server">

    Function CreateDataSource() As ICollection
        Dim dt As New DataTable()
        Dim dr As DataRow

        dt.Columns.Add(New DataColumn("IntegerValue", GetType(Int32)))
        dt.Columns.Add(New DataColumn("StringValue", GetType(String)))
        dt.Columns.Add(New DataColumn("DateTimeValue", GetType(DateTime)))
        dt.Columns.Add(New DataColumn("BoolValue", GetType(Boolean)))
        dt.Columns.Add(New DataColumn("CurrencyValue", GetType(Double)))

        Dim i As Integer
        For i = 0 To 8
            dr = dt.NewRow()

            dr(0) = i
            dr(1) = "Item " + i.ToString()
            dr(2) = DateTime.Now
            If (i Mod 2) <> 0 Then
                dr(3) = True
            Else
                dr(3) = False
            End If
            dr(4) = 1.23 *(i + 1)

            dt.Rows.Add(dr)
        Next i

        Dim dv As New DataView(dt)
        Return dv
    End Function

    Sub Page_Load(sender As Object, e As EventArgs)
        If Not IsPostBack Then
            CheckBoxList1.DataSource = CreateDataSource()
            CheckBoxList1.DataTextField = "StringValue"
            CheckBoxList1.DataValueField = "CurrencyValue"
            CheckBoxList1.DataBind()
        End If
    End Sub

    Sub Index_Changed(sender As Object, e As EventArgs)        
        Label1.Text = "The index of the first item selected is: " & _
            CheckBoxList1.SelectedIndex.ToString()
    End Sub

 </script>

 <head runat="server">
    <title>ASP.NET Example</title>
</head>
<body>

    <form id="form1" runat="server">

       <asp:CheckBoxList id="CheckBoxList1" 
            OnSelectedIndexChanged="Index_Changed"
            AutoPostBack="true"
            runat="server"/>

       <br />

       <asp:Label id="Label1" runat="server"/>

    </form>

 </body>
 </html>
C#

<%@ Page Language="C#" AutoEventWireup="True" %>
<%@ Import Namespace="System.Data" %>

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
 <script language="c#" runat="server">

    ICollection CreateDataSource() {
       DataTable dt = new DataTable();
       DataRow dr;

       dt.Columns.Add(new DataColumn("IntegerValue", typeof(Int32)));
       dt.Columns.Add(new DataColumn("StringValue", typeof(string)));
       dt.Columns.Add(new DataColumn("DateTimeValue", typeof(DateTime)));
       dt.Columns.Add(new DataColumn("BoolValue", typeof(bool)));
       dt.Columns.Add(new DataColumn("CurrencyValue", typeof(double)));

       for (int i = 0; i < 9; i++) {
          dr = dt.NewRow();

          dr[0] = i;
          dr[1] = "Item " + i.ToString();
          dr[2] = DateTime.Now;
          dr[3] = (i % 2 != 0) ? true : false;
          dr[4] = 1.23 * (i+1);

          dt.Rows.Add(dr);
       }

       DataView dv = new DataView(dt);
       return dv;
    }

    void Page_Load(Object sender, EventArgs e) {
       if (!IsPostBack) {
          CheckBoxList1.DataSource = CreateDataSource();
          CheckBoxList1.DataTextField="StringValue";
          CheckBoxList1.DataValueField="CurrencyValue";
          CheckBoxList1.DataBind();
       }
    }

    void Index_Changed(Object sender, EventArgs e) {

       Label1.Text = "The index of the first item selected is: " + 
                     CheckBoxList1.SelectedIndex.ToString(); 

    }

 </script>

 <head runat="server">
    <title>ASP.NET Example</title>
</head>
<body>

    <form id="form1" runat="server">

       <asp:CheckBoxList id="CheckBoxList1" 
            OnSelectedIndexChanged="Index_Changed"
            AutoPostBack="true"
            runat="server"/>

       <br />

       <asp:Label id="Label1" runat="server"/>

    </form>

 </body>
 </html>
Version Information

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0
Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
See Also

Reference

ListControl Class
System.Web.UI.WebControls Namespace
CheckBoxList