Generating Multi Level Menu through Recursion in C#

Introduction

This article will explain how to build a multi-level menu using recursion method.

Output

Detail

We have following menu model class

public class Menu
{
 public int Id { get; set; }
 public string Name { get; set; }
 public int ParenetId { get; set; }
 public string Url { get; set; }
}

Now create a method that generate different levels or you can access it from RDMS.

public List<Menu> GetMenuItems()
{
 List<Menu> MenuItmes = new List<Menu>();
 Menu item1 = new Menu { Id = 1, Name = "Item1" };
 Menu item2 = new Menu { Id = 2, Name = "Item2" };
 Menu item3 = new Menu { Id = 3, Name = "Item2_1", ParenetId = 2 };
 Menu item4 = new Menu { Id = 4, Name = "Item2_2", ParenetId = 2 };
 Menu item5 = new Menu { Id = 5, Name = "Item2_2_1", ParenetId = 4 };
 Menu item6 = new Menu { Id = 6, Name = "Item2_2_2", ParenetId = 4 };
 Menu item7 = new Menu { Id = 7, Name = "Item2_2_1_1", ParenetId = 5 };
 Menu item8 = new Menu { Id = 8, Name = "Item1_1", ParenetId = 1 };

 MenuItmes.Add(item1);
 MenuItmes.Add(item2);
 MenuItmes.Add(item3);
 MenuItmes.Add(item4);
 MenuItmes.Add(item5);
 MenuItmes.Add(item6);
 MenuItmes.Add(item7);
 MenuItmes.Add(item8);

 return MenuItmes;

}

Full code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;

namespace TestProject.Models
{

    public class Menu
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int ParenetId { get; set; }
        public string Url { get; set; }
    }

    public class MenuRecursion
    {
        List<Menu> allMenuItems;
        public const string OPEN_LIST_TAG = "<ul>";
        public const string CLOSE_LIST_TAG = "</ul>";
        public const string OPEN_LIST_ITEM_TAG = "<li>";
        public const string CLOSE_LIST_ITEM_TAG = "</li>";

        public MenuRecursion()
        {
            allMenuItems = GetMenuItems();
        }
        public List<Menu> GetMenuItems()
        {
            List<Menu> MenuItmes = new List<Menu>();
            Menu item1 = new Menu { Id = 1, Name = "Item1" };
            Menu item2 = new Menu { Id = 2, Name = "Item2" };
            Menu item3 = new Menu { Id = 3, Name = "Item2_1", ParenetId = 2 };
            Menu item4 = new Menu { Id = 4, Name = "Item2_2", ParenetId = 2 };
            Menu item5 = new Menu { Id = 5, Name = "Item2_2_1", ParenetId = 4 };
            Menu item6 = new Menu { Id = 6, Name = "Item2_2_2", ParenetId = 4 };
            Menu item7 = new Menu { Id = 7, Name = "Item2_2_1_1", ParenetId = 5 };
            Menu item8 = new Menu { Id = 8, Name = "Item1_1", ParenetId = 1 };

            MenuItmes.Add(item1);
            MenuItmes.Add(item2);
            MenuItmes.Add(item3);
            MenuItmes.Add(item4);
            MenuItmes.Add(item5);
            MenuItmes.Add(item6);
            MenuItmes.Add(item7);
            MenuItmes.Add(item8);

            return MenuItmes;

        }

        public string GenerateMenuUi()
        {
            var strBuilder = new StringBuilder();
            List<Menu> parentItems = (from a in allMenuItems where a.ParenetId == 0 select a).ToList();
            strBuilder.Append(OPEN_LIST_TAG);
            foreach (var parentcat in parentItems)
            {
                strBuilder.Append(OPEN_LIST_ITEM_TAG);
                strBuilder.Append(parentcat.Name);               
                List<Menu> childItems = (from a in allMenuItems where a.ParenetId == parentcat.Id select a).ToList();
                if (childItems.Count > 0)
                    AddChildItem(parentcat, strBuilder);
                strBuilder.Append(CLOSE_LIST_ITEM_TAG);
            }
            strBuilder.Append(CLOSE_LIST_TAG);
            return strBuilder.ToString();
        }

        private void AddChildItem(Menu childItem, StringBuilder strBuilder)
        {
            strBuilder.Append(OPEN_LIST_TAG);
            List<Menu> childItems = (from a in allMenuItems where a.ParenetId == childItem.Id select a).ToList();
            foreach (Menu cItem in childItems)
            {
                strBuilder.Append(OPEN_LIST_ITEM_TAG);
                strBuilder.Append(cItem.Name);
                List<Menu> subChilds = (from a in allMenuItems where a.ParenetId == cItem.Id select a).ToList();
                if (subChilds.Count > 0)
                {
                    AddChildItem(cItem, strBuilder);
                }
                strBuilder.Append(CLOSE_LIST_ITEM_TAG);
            }
            strBuilder.Append(CLOSE_LIST_TAG);            
        }
    }
}

Example

In Action method

public ActionResult Index()
{
 var menuRecursion = new MenuRecursion();
 var menuUi = menuRecursion.GenerateMenuUi();
 ViewBag.Menu = menuUi;
 return View();
}

In View page

 @Html.Raw(ViewBag.Menu)

Output

Conclusion

In above we see how to create multi-level menu through recursion using string-builder. Hope it will be helpful.