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TreeView.TreeNodeExpanded Event

Note: This event is new in the .NET Framework version 2.0.

Occurs when a node is expanded in the TreeView control.

Namespace: System.Web.UI.WebControls
Assembly: System.Web (in system.web.dll)

Public Event TreeNodeExpanded As TreeNodeEventHandler
Dim instance As TreeView
Dim handler As TreeNodeEventHandler

AddHandler instance.TreeNodeExpanded, handler

/** @event */
public void add_TreeNodeExpanded (TreeNodeEventHandler value)

/** @event */
public void remove_TreeNodeExpanded (TreeNodeEventHandler value)

JScript supports the use of events, but not the declaration of new ones.

The TreeNodeExpanded event is raised when a node is expanded in the TreeView control. This allows you to provide an event-handling method that performs a custom routine whenever this event occurs.


If the SelectAction property for a node is set to TreeNodeSelectAction.Expand or TreeNodeSelectAction.SelectExpand, the TreeNodeExpanded event is also raised when that node is clicked in the TreeView control.

For more information about handling events, see Consuming Events.

The following code example demonstrates how to use the TreeNodeExpanded event to update the content of a Label control when the user expands a node in the TreeView control.

<%@ Page Language="VB" %>

<script runat="server">

  Sub Node_Expand(ByVal sender As Object, ByVal e As TreeNodeEventArgs)

    Message.Text = "You expanded the " & e.Node.Text & " node."

  End Sub

  Sub Node_Collapse(ByVal sender As Object, ByVal e As TreeNodeEventArgs)

    Message.Text = "You collapsed the " & e.Node.Text & " node."

  End Sub



    <form runat="server">
      <h3>TreeView TreeNodeExpand and TreeNodeCollapse Example</h3>
      <asp:TreeView id="BookTreeView"
          <asp:TreeNode Value="Chapter 1" 
            Text="Chapter 1">
            <asp:TreeNode Value="Section 1"
              Text="Section 1">
              <asp:TreeNode Value="Paragraph 1" 
                Text="Paragraph 1">
            <asp:TreeNode Value="Section 2" 
              Text="Section 2">
      <asp:Label id="Message" runat="server"/>


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

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

.NET Framework

Supported in: 2.0