C# hashtable example of caching online number of online users

Websites often need to cache the number of online users. Hashtable is a good choice. After all, access is very convenient and fast, and offline members can be deleted at any time to reduce the pressure on the server.

A static Hashtable must be defined, otherwise it cannot be cached; the "Hashtable.Synchronized" means that Hashtable is synchronized between processes to avoid errors. This class basically implements the methods to be used, just call it.

C# hashtable example of caching online number of online users

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

public class OnLineUser
       {
              private static Hashtable ht = Hashtable.Synchronized(new Hashtable());

       /// <summary>
              /// Add members to Hashtable
              /// <summary>
              /// <param name="userId">Member ID</param>
              public static void AddUser(string userId)
              {
                     if(!ht.Contains(userId))
                            ht[userId] = DateTime.Now;
              }

       /// <summary>
              /// Check if the member is online
              /// <summary>
              /// <param name="userId">Member ID</param>
              /// <param name="t">Do not request for more than a few minutes as offline</param>
              /// <returns>true: online; false: not online</returns>
              public static bool IsOnLineUser(string userId, int t)
              {
                     if(ht.Contains(userId))
                     {
                            DateTime dt = (DateTime)ht[userId];
                            if(GetMinutes(DateTime.Now, dt) > t)
                                   return true;
                            else
                                   return false;
                     }
                     else
                            return false;
              }

       /// <summary>
              /// Show all online members
              /// <summary>
              /// <returns>ll online members</returns>
              public static string ShowOnLineUser()
              {
                     if(ht.Count > 0)
                     {
                            StringBuilder sb = new StringBuilder();
                            foreach(DictionaryEntry de in ht)
                                   sb += de.Value.ToSting();
                     }
                     return sb.ToSting();
              }

              /// <summary>
              /// Take two time intervals(minutes)
              /// </summary>
              /// <param name="newTime">New time</param>
              /// <param name="oldTime">Old time</param>
              /// <returns>Two time intervals</returns>
              public static int GetMinutes(DateTime dt1, DateTime dt2)
              {
                     TimeSpan ts1 = new TimeSpan(dt1.Ticks);
                     TimeSpan ts2 = new TimeSpan(dt2.Ticks);
                     TimeSpan ts = ts1.Subtract(ts2).Duration();
                     return (int)ts.TotalMinutes;
              }
       }