怎么能知道指定Session用户当前是否在线

/// <summary>
/// 在线用户信息管理类
/// </summary>
public class OnlineManage
{
    private static OnlineManage _instance = new OnlineManage();
    //private Dictionary<int, OnlineUserInfo> _onlineUserList = new Dictionary<int, OnlineUserInfo>();
    private Dictionary<string, OnlineUserInfo> _onlineSession = new Dictionary<string, OnlineUserInfo>();

    public const int Timeout_Minutes = 20;  //非登录会员在线用户过期时间
    public const int Timeout_Minutes_Member = 40; //登录会员在线过期时间

    private OnlineManage()
    {
    }

    public void Clear()
    {
        lock(this)
        {
            //_onlineUserList.Clear();
            _onlineSession.Clear();
        }
    }

    /// <summary>
    /// 获取当前在线用户总数(包含登录和未登录的)
    /// </summary>
    public int Count
    {
        get { return _onlineSession.Count; }
    }

    /// <summary>
    /// 在线会员数
    /// </summary>
    public int MemberCount
    {
        get
        {
            int iRet = 0;
            lock(this)
            {
                foreach (string _sKey in _onlineSession.Keys)
                {
                    OnlineUserInfo oInfo = _onlineSession[_sKey];
                    if (oInfo == null)
                    {
                        _onlineSession.Remove(_sKey);
                    }
                    else
                    {
                        if (oInfo.UserID>0)
                        {
                            iRet++;
                        }
                    }
                }
            }
            return iRet;
        }
    }

    public OnlineUserInfo this[int UserID]
    {
        get
        {
            lock(this)
            {
                foreach (string _sKey in _onlineSession.Keys)
                {
                    OnlineUserInfo oInfo = _onlineSession[_sKey];
                    if (oInfo == null)
                    {
                        _onlineSession.Remove(_sKey);
                    }
                    else
                    {
                        if (oInfo.UserID == UserID)
                        {
                            return oInfo;
                        }
                    }
                }
                return null;
            }
        }
    }

    public OnlineUserInfo this[string sSessionID]
    {
        get
        {
            if (_onlineSession.ContainsKey(sSessionID))
                return _onlineSession[sSessionID];
            else
                return null;
        }
    }

    /// <summary>
    /// 获取所有当前在线用户的ID数组
    /// </summary>
    public int[] OnlineUserIDs
    {
        get
        {
            lock(this)
            {
                List<int> ids = new List<int>();
                foreach(string _sKey in _onlineSession.Keys)
                {
                    OnlineUserInfo oInfo = this[_sKey];
                    if(oInfo!=null && oInfo.UserID>0)
                    {
                        ids.Add(oInfo.UserID);
                    }
                }
                return ids.ToArray();
            }
        }
    }

    /// <summary>
    /// 用户有活动，存在异常情况：
    /// 1. Session未结束，但是换了用户登录
    /// </summary>
    /// <param name="UserID"></param>
    public void UserActived(string sSessionID,int iUserID)
    {
        lock (this)
        {
            OnlineUserInfo oInfo = this[sSessionID];
            if (oInfo == null)
            {
                oInfo = new OnlineUserInfo(sSessionID, iUserID);
                _onlineSession.Add(sSessionID, oInfo);
            }
            else
            {
                if(oInfo.UserID != iUserID) //考虑同一个页面先后用别的帐号登录
                {
                    oInfo.UserID = iUserID;
                    oInfo.LoginTime = DateTime.Now;
                }
                oInfo.LastActiveTime = DateTime.Now;
            }
        }
    }

    /// <summary>
    /// 用户离开（未活动时间超时或者用户注销了）
    /// </summary>
    /// <param name="UserID"></param>
    public void UserLeaved(string sSessionID,int iUserID)
    {
        lock(this)
        {
            _onlineSession.Remove(sSessionID);
        }
    }

    /// <summary>
    /// 用户离开（未活动时间超时或者用户注销了）
    /// </summary>
    /// <param name="sSessionID"></param>
    public void UserLeaved(string sSessionID)
    {
        lock (this)
        {
            _onlineSession.Remove(sSessionID);
        }
    }


    /// <summary>
    /// 检查在线用户状态，如果发现有超时未活动的用户，将其删除
    /// </summary>
    public void CheckOnlineUsers()
    {
        lock(this)
        {
            //1.先查询出需要删除的Key列表
            List<string> _removeKeys = new List<string>();
            foreach (KeyValuePair<string, OnlineUserInfo> kvp in _onlineSession)
            {
                OnlineUserInfo oInfo = kvp.Value;
                string _sKey = kvp.Key;
                if(oInfo == null)
                {
                    _removeKeys.Add(_sKey);
                }
                else
                {
                    if(oInfo.UserID>0) //登录会员
                    {
                        if (oInfo.NoActiveMinutes > Timeout_Minutes_Member)
                        {
                            _removeKeys.Add(_sKey);
                        }
                    }
                    else //未登录会员
                    {
                        if (oInfo.NoActiveMinutes > Timeout_Minutes)
                        {
                            _removeKeys.Add(_sKey);
                        }
                    }
                }
            }

            //2.从容器中删除这些Key
            foreach (string _key in _removeKeys)
            {
                _onlineSession.Remove(_key);
            }
            _removeKeys.Clear();
        }
    }

    /// <summary>
    /// 获取唯一实例
    /// </summary>
    /// <returns></returns>
    public static OnlineManage GetInstance()
    {
        return _instance;
    }
}

/// <summary>
/// 在线用户信息类
/// </summary>
public class OnlineUserInfo
{
    public int UserID;
    public string SessionID;
    public DateTime LoginTime;
    public DateTime LastActiveTime;

    /// <summary>
    /// 构造函数，用于用户新登录时创建用户在线条目
    /// </summary>
    /// <param name="iUserID">活动的用户ID</param>
    /// <param name="dtLoginTime">用户活动时间</param>
    public OnlineUserInfo(int iUserID,DateTime dtLoginTime)
    {
        UserID = iUserID;
        SessionID = "";
        LoginTime = dtLoginTime;
        LastActiveTime = dtLoginTime;
    }

    /// <summary>
    /// 构造函数，用于用户新登录时创建用户在线条目
    /// </summary>
    /// <param name="iUserID">活动的用户ID</param>
    /// <param name="dtLoginTime">用户活动时间</param>
    public OnlineUserInfo(string sSessionID, int iUserID)
    {
        UserID = iUserID;
        LoginTime = DateTime.Now;
        LastActiveTime = DateTime.Now;
        SessionID = sSessionID;
    }

    /// <summary>
    /// 用户初次进来并创建了新Session
    /// </summary>
    /// <param name="sSessionID"></param>
    public OnlineUserInfo(string sSessionID)
    {
        UserID = 0;
        LoginTime = DateTime.Now;
        LastActiveTime = DateTime.Now;
        SessionID = sSessionID;
    }

    /// <summary>
    /// 获取该用户的未活动时长（分钟数）
    /// </summary>
    public int NoActiveMinutes
    {
        get
        {
            TimeSpan dtSpan = DateTime.Now.Subtract(LastActiveTime);
            return (int)dtSpan.TotalMinutes;
        }
    }

    /// <summary>
    /// 获取该用户的在线时长（分钟数）
    /// </summary>
    public int OnlineMinutes
    {
        get
        {
            TimeSpan dtSpan = DateTime.Now.Subtract(LoginTime);
            return (int)dtSpan.TotalMinutes;
        }
    }
}

------解决方案--------------------
该结贴给分了

------解决方案--------------------
http://blog.****.net/xiyongjie/archive/2008/10/13/3068682.aspx
这个Blog里给了完整的处理方法,可以参考下~

------解决方案--------------------