ASP.NET

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <div id="HomeLink">
        <asp:HyperLink ID="HyperLink1" runat="server" CssClass="home" ImageUrl="~/Images/105329-3d-glossy-orange-orb-icon-business-home5.png"
            NavigateUrl="~/Default.aspx">
        </asp:HyperLink>
    </div>
    <asp:Panel ID="TreeArea" runat="server" CssClass="TreeArea">
        <%-- Here ExpandDepth="0" for eleminates the expansion of the added treenodes --%>
        <asp:TreeView ID="TreeViewSettings" runat="server" ExpandDepth="0" PopulateNodesFromClient="False"
            CssClass="TreeViewSettings" OnSelectedNodeChanged="TreeViewSettings_SelectedNodeChanged">
        </asp:TreeView>
    </asp:Panel>
    <asp:Panel ID="EditFormArea" runat="server" CssClass="SettingsFormArea">
        <asp:UpdatePanel ID="UpdatePanelEdit" runat="server">
            <ContentTemplate>
                <asp:Panel ID="PanelEdit" runat="server">
                </asp:Panel>
            </ContentTemplate>
            <Triggers>
                <asp:AsyncPostBackTrigger ControlID="TreeViewSettings" EventName="SelectedNodeChanged">
                </asp:AsyncPostBackTrigger>
            </Triggers>
        </asp:UpdatePanel>
    </asp:Panel>
</asp:Content>

protected void TreeViewSettings_SelectedNodeChanged(object sender, EventArgs e)
{
    reload();
}
protected void reload(){
    TreeNode selection = TreeViewSettings.SelectedNode;
    string[] SelectedDetails = selection.Value.Split(new char[] {'|'});
    RegionEditor RegionEditorForm = LoadControl("~/TheSettings/RegionEditor.ascx") as RegionEditor;
    RegionEditorForm.RegionID = int.Parse(SelectedDetails[1]);
    RegionEditorForm.CancelClick += new EventHandler(RegionEditorForm_CancelClick);
    PanelEdit.Controls.Add(RegionEditorForm);
    AsyncPostBackTrigger CancelTrigger = new AsyncPostBackTrigger();
    CancelTrigger.ControlID = RegionEditorForm.UniqueID;
    CancelTrigger.EventName = "CancelClick";
    UpdatePanelEdit.Triggers.Add(CancelTrigger);
}
void RegionEditorForm_CancelClick(object sender, EventArgs e)
{
    reload();
}

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="RegionEditor.ascx.cs"
    Inherits="Shedulinator.TheSettings.RegionEditor" %>
<% if (false)
   { %>
<link rel="Stylesheet" type="text/css" href="../Styles/Site.css" />
<% } %>
<asp:Image ID="Image1" runat="server" ImageUrl="~/Images/106660-3d-glossy-orange-orb-icon-transport-travel-compass2.png"
    CssClass="SettingsIcon" />
<asp:Panel ID="Panel1" runat="server" CssClass="SettingsFormPanel">
    <asp:Label ID="LabelRegion" runat="server" Text="Region Name:"></asp:Label>
    <asp:TextBox ID="TextBoxRegionName" runat="server"></asp:TextBox>
    <asp:Button ID="ButtonCancel" runat="server" CssClass="SettingsButton" 
        Text="Cancel" onclick="ButtonCancel_Click" />
    <asp:Button ID="ButtonOK" runat="server" CssClass="SettingsButton" Text="OK" 
        onclick="ButtonOK_Click" />
</asp:Panel>

public partial class RegionEditor : System.Web.UI.UserControl
{
    public event EventHandler CancelClick;
    protected void Page_Load(object sender, EventArgs e)
    {
    }
    protected void ButtonCancel_Click(object sender, EventArgs e)
    {
        if (CancelClick != null)
        {
            CancelClick(this, new EventArgs());
        }
    }
}