using System;

using System.Collections.Generic;

public class Program

{

    public class ContentKey

    {

        public int key_num = 0;

    }

    public static void Main(string[] args)

    {

        ContentKey a = new ContentKey() {key_num = 10};

        ContentKey b = new ContentKey() {key_num = 20};

        ContentKey c = new ContentKey() {key_num = 30};

        SortedDictionary<ContentKey, string> dict = new SortedDictionary<ContentKey, string>(new KeyComparer());

        dict.Add(a, "A");

        dict.Add(c, "C");

        dict.Add(b, "B");

        foreach(var key_value in dict)

        {

            Console.WriteLine("Key val: " + key_value.Key.key_num + " Str: " + key_value.Value);

        }

​

        a.key_num = 50;

        foreach(var key_value in dict)

        {

            Console.WriteLine("Key val: " + key_value.Key.key_num + " Str: " + key_value.Value);

        }

​

    }

    public class KeyComparer : IComparer<ContentKey>

    {

        public int Compare(ContentKey a, ContentKey b)

        {

            return a.key_num.CompareTo(b.key_num);

        }

    }

}