Windows Forms TreeView Hierarchy Binding using IHierarchyData/IHierarchyEnumerable

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Web.UI;
using System.Windows.Forms;

namespace TreeHierarchyTest
{
    public partial class TreeViewHierarchyBinding : Component
    {
        private IHierarchyData dataSource;
        private TreeView treeView;
        private Dictionary<TreeNode, IHierarchyData> nodeDictionary = new
            Dictionary<TreeNode, IHierarchyData>();

        public TreeViewHierarchyBinding()
        {
            InitializeComponent();
        }

        public TreeViewHierarchyBinding(IContainer container)
        {
            container.Add(this);

            InitializeComponent();
        }

        #region TreeView Events

        private void RegisterEvents(TreeView tv)
        {
            tv.BeforeExpand += TreeViewBeforeExpand;
        }

        private void UnregisterEvents(TreeView tv)
        {
            tv.BeforeExpand -= TreeViewBeforeExpand;
        }

        private void TreeViewBeforeExpand(object sender, TreeViewCancelEventArgs e)
        {
            if (e.Node.Checked)
            {
                return;
            }
            IHierarchyData hierarchyData;
            if (nodeDictionary.TryGetValue(e.Node, out hierarchyData))
            {
                PopulateChildNodes(e.Node.Nodes, hierarchyData.GetChildren());
                e.Node.Checked = true;
            }
        }

        #endregion

        #region TreeView Population

        private void PopulateChildNodes(TreeNodeCollection parentCollection,
            IHierarchicalEnumerable children)
        {
            parentCollection.Clear();
            foreach (object child in children)
            {
                IHierarchyData childData = children.GetHierarchyData(child);
                TreeNode childNode = new TreeNode(childData.ToString());
                if (childData.HasChildren)
                {
                    childNode.Nodes.Add("Dummy");   // Make expandable
                }
                nodeDictionary.Add(childNode, childData);
                parentCollection.Add(childNode);
            }
        }

        private void UpdateRootNodes(TreeView tv, IHierarchyData hierarchyData)
        {
            if (tv == null)
            {
                return;
            }
            tv.Nodes.Clear();
            if (hierarchyData != null)
            {
                IHierarchicalEnumerable roots = hierarchyData.GetChildren();
                PopulateChildNodes(tv.Nodes, roots);
            }
        }

        #endregion

        [Browsable(false)]
        [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
        public IHierarchyData DataSource
        {
            get { return dataSource; }
            set
            {
                if (value != dataSource)
                {
                    dataSource = value;
                    nodeDictionary.Clear();
                    UpdateRootNodes(treeView, value);
                }
            }
        }

        [Category("Behavior")]
        [DefaultValue(null)]
        [Description("Specifies the TreeView that the hierarchy should be bound to.")]
        public TreeView TreeView
        {
            get { return treeView; }
            set
            {
                if (value != treeView)
                {
                    if (treeView != null)
                    {
                        UnregisterEvents(treeView);
                    }
                    treeView = value;
                    nodeDictionary.Clear();
                    RegisterEvents(value);
                    UpdateRootNodes(treeView, dataSource);
                }
            }
        }
    }
}