ASPxTreeView.ExpandedChanging Event

Fires before the expansion state of a node is changed by end-user interaction.

Namespace: DevExpress.Web

Assembly: DevExpress.Web.v19.1.dll

Declaration

C#

public event TreeViewNodeCancelEventHandler ExpandedChanging

VB.NET

Public Event ExpandedChanging As TreeViewNodeCancelEventHandler

Event Data

The ExpandedChanging event's data class is TreeViewNodeCancelEventArgs. The following properties provide information specific to this event:

Property	Description
Cancel	Gets or sets a value indicating whether the action that raised the event should be canceled.
Node	Gets a node object related to the event. Inherited from TreeViewNodeEventArgs.

Remarks

Write an ExpandedChanging event handler to perform specific actions before each time a node’s expansion state is changed by end-user interaction. You can use the event parameter’s properties to identify the node being manipulated and cancel execution of the command, if necessary.

Example

The sample code below represents an ASPxTreeView.ExpandedChanging event handler. The event handler prevents collapsing nodes if it has selected children in any generation.

Note

A complete sample project is available at https://github.com/DevExpress-Examples/how-to-prevent-parent-node-collapsing-e2439

Default.aspx.cs

using DevExpress.Web.ASPxTreeView;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void ASPxTreeView1_ExpandedChanging(object source, DevExpress.Web.ASPxTreeView.TreeViewNodeCancelEventArgs e) {
        if ((e.Node.Expanded) && (ASPxTreeView1.SelectedNode != null)) {
            TreeViewNode  node = ASPxTreeView1.SelectedNode.Parent;
            while (node != null) {
                if (e.Node == node) {
                    e.Cancel = true;
                    break;
                }
                node = node.Parent;
            }
        }
    }
}

Default.aspx (C#)

<dx:ASPxTreeView ID="ASPxTreeView1" runat="server" DataSourceID="XmlDataSource1" AutoPostBack="True" AllowSelectNode="True" OnExpandedChanging="ASPxTreeView1_ExpandedChanging">
</dx:ASPxTreeView>
<asp:XmlDataSource ID="XmlDataSource1" runat="server" DataFile="~/App_Data/MenuTabbedMenu.xml"
    XPath="/mainmenu/item"></asp:XmlDataSource>

Default.aspx (VB.NET)

<dx:ASPxTreeView ID="ASPxTreeView1" runat="server" DataSourceID="XmlDataSource1" AutoPostBack="True" AllowSelectNode="True" OnExpandedChanging="ASPxTreeView1_ExpandedChanging">
 </dx:ASPxTreeView>
 <asp:XmlDataSource ID="XmlDataSource1" runat="server" DataFile="~/App_Data/MenuTabbedMenu.xml"
     XPath="/mainmenu/item"></asp:XmlDataSource>

Default.aspx.vb

Imports DevExpress.Web.ASPxTreeView

Partial Public Class _Default
    Inherits System.Web.UI.Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

    End Sub
    Protected Sub ASPxTreeView1_ExpandedChanging(ByVal source As Object, ByVal e As DevExpress.Web.ASPxTreeView.TreeViewNodeCancelEventArgs)
        e.Node.Expanded = True
        If e.Node.Expanded AndAlso (ASPxTreeView1.SelectedNode IsNot Nothing) Then
            Dim node As TreeViewNode = ASPxTreeView1.SelectedNode.Parent
            Do While node IsNot Nothing
                If e.Node Is node Then
                    e.Cancel = True
                    Exit Do
                End If
                node = node.Parent
            Loop
        End If
    End Sub
End Class