How to: Prohibit Collapsing Nodes

• Aug 01, 2019

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