ListBox.SelectedValue always returns nothing

johnuk1 · Sep 26, 2004

I have a asp.net page with a listbox, a textbox and a button. I simply populate the listbox on the page_load method with a couple of items. I then click an item however the textbox never gets populated. If i instead populate the textbox with the selectedindex of the listbox. In this case i always get -1 ie nothing selected.
in addition if i change the code behing the button to set the textbox go Listbox1.items.count it return 1 ie there is an item there!!!

why can i set another textbox to the correct number of items in the listbox but cannot reference the selected item directly?

johnuk1 · Sep 26, 2004

here is the hhtml for the page

<%@ Page language="c#" Codebehind="test.aspx.cs" AutoEventWireup="false" Inherits="test" enableViewState="False"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<title>test</title>
<link href="template.css" type="text/css" rel="stylesheet">
<meta name="GENERATOR" Content="Microsoft Visual Studio .NET 7.1">
<meta name="CODE_LANGUAGE" Content="C#">
<meta name="vs_defaultClientScript" content="JavaScript">
<meta name="vs_targetSchema" content="

http://schemas.microsoft.com/intellisense/ie5">

</HEAD>
<body MS_POSITIONING="GridLayout" bgColor="steelblue">
<form id="Form1" method="post" runat="server">
<asp:ListBox id="ListBox1" style="Z-INDEX: 101; LEFT: 0px; POSITION: absolute; TOP: 40px" runat="server"
Width="300px" Height="120px" SelectionMode="Multiple"></asp:ListBox>
<asp:Button id="btEscalate" style="Z-INDEX: 102; LEFT: 88px; POSITION: absolute; TOP: 176px"
runat="server" Width="100px" Height="24px" Text="OK" CausesValidation="False"></asp:Button>
<asp:TextBox id="TextBox2" style="Z-INDEX: 103; LEFT: 24px; POSITION: absolute; TOP: 216px" runat="server"
Width="264px"></asp:TextBox>
<asp:Button id="btCancel" style="Z-INDEX: 104; LEFT: 200px; POSITION: absolute; TOP: 176px"
runat="server" Height="24px" Width="100px" Text="Cancel"></asp:Button>
<asp:Label id="Label1" style="Z-INDEX: 105; LEFT: 0px; POSITION: absolute; TOP: 0px" runat="server"
Height="40px" Width="300px" BackColor="CornflowerBlue" Font-Bold="True">Escalate to Queue</asp:Label>
</form>
</body>
</HTML>

adamroof · Sep 27, 2004

Heres how i handle multiple selection of email address to add to a cc field...

Code:

Dim item As ListItem
Dim strCC As String
   For Each item In ccLBox.Items
      If item.Selected Then
	strCC = strCC & item.Value & ";"
      End If
   Next item

its gotta be in your code, not your html

jmeckley · Sep 27, 2004

I believe there is also a SelectedItems property to a list box control.

Code:

Dim item As ListItem
Dim strCC As New System.Text.StringBuilder

  For Each item In ccLBox.SelectedItems
    strCC.append(item.Value & ";")
  Next item

  ccTextBox.Text =  strCC.ToString

see faq855-1882 [tt]String Concatenation in VB.NET [/tt]for why I chose a stringbuilder data type over a string data type

Jason Meckley
Database Analyst
WITF

BoulderBum · Sep 27, 2004

why can i set another textbox to the correct number of items in the listbox but cannot reference the selected item directly?"

You're probably resetting the items each time in Page_Load, which resets the index.

If you have a line of code like:

myListBox.DataBind();

Make sure that you only populate it once by checking for !IsPostBack before binding:

if( !Page.IsPostBack )
{
myListBox.DataBind();
}

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ListBox.SelectedValue always returns nothing

johnuk1

MIS

johnuk1

MIS

adamroof

Programmer

jmeckley

Programmer

BoulderBum

Programmer

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