Collapse all Open Nodes Of an ASP.NET TreeView when Another Node is expanded

Users have a very common requirement around the ASP.NET TreeView - that is to keep only one TreeNode expanded at a given point of time. So if a TreeNode in the TreeView is expanded, collapse the other open TreeNodes. Here's how to do so:

 <asp:TreeView ID="TreeView1" runat="server"

        ontreenodeexpanded="TreeView1_TreeNodeExpanded">

        <Nodes>

            <asp:TreeNode Text="Node1" Value="Node1">

                <asp:TreeNode Text="Node1.1" Value="Node1.1"/>

                <asp:TreeNode Text="Node1.2" Value="Node1.2"/>

                <asp:TreeNode Text="Node1.3" Value="Node1.3"/>

            </asp:TreeNode>

            <asp:TreeNode Text="Node2" Value="Node2">

                <asp:TreeNode Text="Node1.1" Value="Node2.1"/>

                <asp:TreeNode Text="Node1.2" Value="Node2.2"/>

            </asp:TreeNode>

            <asp:TreeNode Text="Node3" Value="Node3">

                <asp:TreeNode Text="Node3.1" Value="Node3.1"/>

                <asp:TreeNode Text="Node3.2" Value="Node3.2"/>

            </asp:TreeNode>

        </Nodes>

</asp:TreeView>

C#

protected void TreeView1_TreeNodeExpanded(object sender, TreeNodeEventArgs e)

{

    // Loop through all nodes

    foreach (TreeNode treenode in TreeView1.Nodes)

    {

        // If node is expanded

        if (treenode != e.Node)

        {

            // Collapse all other nodes

            treenode.Collapse();    

        }

    }

}

VB.NET

    Protected Sub TreeView1_TreeNodeExpanded(ByVal sender As Object, ByVal e As TreeNodeEventArgs)

        ' Loop through all nodes

        For Each treenode As TreeNode In TreeView1.Nodes

            ' If node is expanded

            If treenode IsNot e.Node Then

                ' Collapse all other nodes

                treenode.Collapse()

            End If

        Next treenode

    End Sub