Customize QuickLaunch Webpart

using System;
using System.Runtime.InteropServices;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Serialization;

using Microsoft.SharePoint;
using Microsoft.SharePoint.Navigation;
using Microsoft.SharePoint.WebControls;
using Microsoft.SharePoint.WebPartPages;
using System.Collections.Specialized;
using System.Collections;
using Microsoft.SharePoint.Utilities;
using System.ComponentModel;

namespace CustomizeQuickLaunch
{
    [Guid("e5fce1f6-1b7c-4ff6-9941-c673deb1108c")]
    public class QuickLaunch : System.Web.UI.WebControls.WebParts.WebPart
    {
        public QuickLaunch()
        {
        }
        
        // A treeview control image set enum variable
        protected TreeViewImageSet _qlFormat;

        
        //property use to change the image set of tree view control
        // Creates a custom property that is an enum.
        // This property will be displayed as a drop-down list in the
        // property pane.
        [Personalizable(PersonalizationScope.Shared), WebBrowsable, WebDisplayName("Format for quick launch"),
        WebDescription("")]
        [DefaultValue(TreeViewImageSet.Arrows)]
        [WebPartStorage(Storage.Personal)]
        [FriendlyName("Format List")]
        [Description("Select a value from the dropdown list.")]
        [Browsable(true)]
        public TreeViewImageSet SelectFormate
        {
            set { _qlFormat = value; }
            get { return _qlFormat; }
        }


        TreeView trViewQL;// tree view control variable
        protected override void CreateChildControls()
        {
            base.CreateChildControls();

            trViewQL = new TreeView();
          // add control to webpart
            this.Controls.Add(trViewQL);
        }

        // method use to build quick launch in treeview control. I put them in OnPreRender methods ?
        // answers is by putting them here it reflects the changes every time webpart property gets change.
        protected override void OnPreRender(EventArgs e)
        {
	    // for mentaining the state of the control. 
            string currentId = "";
            if (System.Web.HttpContext.Current.Request.QueryString.Get("CNID") != null)
            {
                currentId = System.Web.HttpContext.Current.Request.QueryString.Get("CNID").ToString();
            }
            trViewQL.Nodes.Clear();
	     /// apply the image set in the property
            trViewQL.ImageSet = SelectFormate;
            base.OnPreRender(e);
            trViewQL.CollapseAll();

            SPWeb web = SPContext.Current.Web;
	        
	            SPNavigationNodeCollection qlNodes = web.Navigation.QuickLaunch;
                foreach (SPNavigationNode node in qlNodes)
	            {
	                if (node.IsExternal)
                    {
                        bool IsparentOpen = false;
                        TreeNode trParent = new TreeNode();
                        trParent.Text = node.Title;
                        trParent.NavigateUrl = node.Url;

                        SPNavigationNodeCollection children = node.Children;
	                    foreach (SPNavigationNode child in children)
                        {
                            TreeNode trChild = new TreeNode();
                            trChild.Text = child.Title;
				            // set the url for maintaining the state of the control
                            string separate = "";
                            if (child.Url.IndexOf('?') == -1)
                            {
                                separate = "?CNID=";
                            }
                            else
                            {
                                separate = "&CNID=";
                            }
                            trChild.NavigateUrl = child.Url +separate+child.Title;
				
                            if (!IsparentOpen)
                            {
				                // expand the clicked node and collapse others
                                if (currentId.Equals(child.Title))
                                {
                                    trParent.Expanded = true;
                                    trChild.Selected = true;
                                    IsparentOpen = true;
                                }
                                else
                                {
                                    trParent.Expanded = false;
                                }
                            }
                            trParent.ChildNodes.Add(trChild);
	                    }
                        trViewQL.Nodes.Add(trParent);
	                }
	            }
	        
        }

	// render the control
        protected override void Render(HtmlTextWriter writer)
        {
            trViewQL.RenderControl(writer);
        }
    }
}