Csharp/CSharp Tutorial/Class/IEnumerator

Implements IEnumerator

using System;
using System.Collections;
class User {
    public User(string name) { this.name = name; }
    string name;
    public string Name { get { return name; } }
};
class DBManager : IEnumerable {
    public DBManager() {
        onlineUsers.Add(new User("T"));
        onlineUsers.Add(new User("K"));
        onlineUsers.Add(new User("E"));
    }
    ArrayList onlineUsers = new ArrayList();
    public IEnumerator GetEnumerator() {
        return new Enumerator(onlineUsers);
    }
    class Enumerator : IEnumerator {
        const string INVALID_RECORD = "Use MoveNext before calling Current";
        public Enumerator(ArrayList onlineUsers) {
            foreach (User user in onlineUsers) {
                this.onlineUsers.Add(user);
            }
            Reset();
        }
        ArrayList onlineUsers = new ArrayList();
        int index;
        public bool MoveNext() {
            return (++index < onlineUsers.Count);
        }
        public object Current {
            get {
                if (-1 == index)
                    throw new InvalidOperationException(INVALID_RECORD);
                if (index < onlineUsers.Count)
                    return onlineUsers[index];
                else
                    return null;
            }
        }
        public void Reset() { index = -1; }
    }
    static void Main(string[] args) {
        DBManager db = new DBManager();
        IEnumerator e = db.GetEnumerator();
        while (e.MoveNext()) {
            User user = (User)e.Current;
            Console.WriteLine("User={0}", user.Name);
        }
    }
}