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TreeView.TreeNodeExpanded Event

Occurs when a node is expanded in the TreeView control.

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

public event TreeNodeEventHandler TreeNodeExpanded

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.

NoteNote

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="C#" %>

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

  void Node_Expand(Object sender, TreeNodeEventArgs e)
  {

    Message.Text = "You expanded the " + e.Node.Text + " node.";

  }

  void Node_Collapse(Object sender, TreeNodeEventArgs e)
  {

    Message.Text = "You collapsed the " + e.Node.Text + " node.";

  }

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >

  <head runat="server">
    <title>TreeView TreeNodeExpand and TreeNodeCollapse Example</title>
</head>
<body>
    <form id="form1" runat="server">

      <h3>TreeView TreeNodeExpand and TreeNodeCollapse Example</h3>

      <asp:TreeView id="BookTreeView"
        ExpandDepth="1"
        OnTreeNodeExpanded="Node_Expand"
        OnTreeNodeCollapsed="Node_Collapse"
        runat="server">

        <Nodes>

          <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>

            </asp:TreeNode>

            <asp:TreeNode Value="Section 2" 
              Text="Section 2">
            </asp:TreeNode>

          </asp:TreeNode>

        </Nodes>

      </asp:TreeView>

      <br />

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

    </form>
  </body>
</html>

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0
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