Det virker som sådan - jeg skal bare trykke to gange, for at få det til at virke......hver gang - og det bliver folk jo trætte af....
Du får koden:
Default.aspx:
<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>
<html xmlns="
http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
         Test af menustruktur<br />
        <br />
        <br />
        <br />
        <asp:TreeView ID="TreeView1" runat="server" OnSelectedNodeChanged="TreeView1_SelectedNodeChanged"
            ShowExpandCollapse="False">
            <Nodes>
                <asp:TreeNode Expanded="False" PopulateOnDemand="True" SelectAction="SelectExpand"
                    Text="Heste" Value="Heste">
                    <asp:TreeNode Text="Føl 1" Value="Føl 1"></asp:TreeNode>
                    <asp:TreeNode Text="Føl 2" Value="Føl 2"></asp:TreeNode>
                </asp:TreeNode>
                <asp:TreeNode Expanded="False" PopulateOnDemand="True" SelectAction="SelectExpand"
                    Text="Hunde" Value="Hunde">
                    <asp:TreeNode Text="Hvalpe 1" Value="Hvalpe 1"></asp:TreeNode>
                    <asp:TreeNode Text="Hvalpe 2" Value="Hvalpe 2"></asp:TreeNode>
                    <asp:TreeNode Text="Hvalpe 3" Value="Hvalpe 3"></asp:TreeNode>
                </asp:TreeNode>
            </Nodes>
        </asp:TreeView>
        <br />
    </div>
    </form>
</body>
</html>
Default.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.OleDb;
using System.Xml;
using System.Xml.Xsl;
using System.Xml.XPath;
using System.IO;
public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {       
    }
    protected void TreeView1_SelectedNodeChanged(object sender, EventArgs e)
    {
        if (TreeView1.SelectedNode.Expanded == true)
        {
            TreeView1.SelectedNode.CollapseAll();
        }
        else
        {
            TreeView1.SelectedNode.ExpandAll();
        }
    }
}