Detailed explanation of the application of Asp.net SignalR and implementation of group chat function

/// <summary>
 /// SignalR Hub 群聊类
 /// </summary>
 [HubName("groupChatHub")] // 标记名称供js调用
 public class GroupChatHub : Hub
 {
 /// <summary>
 /// 用户名
 /// </summary>
 private string UserName
 {
  get
  {
  var userName = Context.RequestCookies["USERNAME"];
  return userName == null ? "" : HttpUtility.UrlDecode(userName.Value);
  }
 }

 /// <summary>
 /// 在线用户
 /// </summary>
 private static Dictionary<string, int> _onlineUser = new Dictionary<string, int>();

 /// <summary>
 /// 开始连接
 /// </summary>
 /// <returns></returns>
 public override Task OnConnected()
 {
  Connected();
  return base.OnConnected();
 }


 /// <summary>
 /// 重新链接
 /// </summary>
 /// <returns></returns>
 public override Task OnReconnected()
 {
  Connected();
  return base.OnReconnected();
 }


 private void Connected()
 {
  // 处理在线人员
  if (!_onlineUser.ContainsKey(UserName)) // 如果名称不存在，则是新用户
  {

  // 加入在线人员
  _onlineUser.Add(UserName, 1);

  // 向客户端发送在线人员
  Clients.All.publshUser(_onlineUser.Select(i => i.Key));

  // 向客户端发送加入聊天消息
  Clients.All.publshMsg(FormatMsg("系统消息", UserName + "加入聊天"));
  }
  else
  {
  // 如果是已经存在的用户，则把在线链接的个数+1
  _onlineUser[UserName] = _onlineUser[UserName] + 1;
  }

  // 加入Hub Group，为了发送单独消息
  Groups.Add(Context.ConnectionId, "GROUP-" + UserName);
 }


 /// <summary>
 /// 结束连接
 /// </summary>
 /// <param name="stopCalled"></param>
 /// <returns></returns>
 public override Task OnDisconnected(bool stopCalled)
 {
  // 人员链接数-1
  _onlineUser[UserName] = _onlineUser[UserName] - 1;

  // 判断是否断开了所有的链接
  if (_onlineUser[UserName] == 0)
  {
  // 移除在线人员
  _onlineUser.Remove(UserName);

  // 向客户端发送在线人员
  Clients.All.publshUser(_onlineUser.Select(i => i.Key));

  // 向客户端发送退出聊天消息
  Clients.All.publshMsg(FormatMsg("系统消息", UserName + "退出聊天"));
  }

  // 移除Hub Group
  Groups.Remove(Context.ConnectionId, "GROUP-" + UserName);
  return base.OnDisconnected(stopCalled);
 }

 /// <summary>
 /// 发送消息，供客户端调用
 /// </summary>
 /// <param name="user">用户名，如果为0，则是发送给所有人</param>
 /// <param name="msg">消息</param>
 public void SendMsg(string user, string msg)
 {
  if (user == "0")
  {
  // 发送给所有用户消息
  Clients.All.publshMsg(FormatMsg(UserName, msg));
  }
  else
  {
  //// 发送给自己消息
  //Clients.Group("GROUP-" + UserName).publshMsg(FormatMsg(UserName, msg));

  //// 发送给选择的人员
  //Clients.Group("GROUP-" + user).publshMsg(FormatMsg(UserName, msg));


  // 发送给自己消息
  Clients.Groups(new List<string> { "GROUP-" + UserName, "GROUP-" + user }).publshMsg(FormatMsg(UserName, msg));

  }
 }


 /// <summary>
 /// 格式化发送的消息
 /// </summary>
 /// <param name="name"></param>
 /// <param name="msg"></param>
 /// <returns></returns>
 private dynamic FormatMsg(string name, string msg)
 {
  return new { Name = name, Msg = HttpUtility.HtmlEncode(msg), Time = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") };
 }
 }

<script type="text/javascript">
 $(function () {

  // 链接hub
  var ticker = $.connection.groupChatHub;
  $.connection.hub.start();

  // 接收服务端发送的消息
  $.extend(ticker.client, {

  // 接收聊天消息
  publshMsg: function (data) {
   $("#msg").append("<li><span class=&#39;p&#39;>" + data.Name + "：</span>" + data.Msg + " <span class=&#39;time&#39;>" + data.Time + "</span></li>")
   $("#msg").parents("p")[0].scrollTop = $("#msg").parents("p")[0].scrollHeight;
  },

  // 接收在线人员，然后加入Select，以供单独聊天选中
  publshUser: function (data) {
   $("#count").text(data.length);
   $("#users").empty();
   $("#users").append(&#39;<option value="0">所有人</option>&#39;);
   for (var i = 0; i < data.length; i++) {
   $("#users").append(&#39;<option value="&#39; + data[i] + &#39;">&#39; + data[i] + &#39;</option>&#39;)
   }

  }
  });

  // 发送消息按钮
  $("#btn-send").click(function () {
  var msg = $("#txt-msg").val();
  if (!msg) {
   alert(&#39;请输入内容！&#39;); return false;
  }
  $("#txt-msg").val(&#39;&#39;);

  // 主动发送消息，传入发送给谁，和发送的内容。
  ticker.server.sendMsg($("#users").val(), msg);
  });

 });
 </script>

<h2>
 群聊系统（<span id="count">1</span>人在线）：@ViewBag.UserName
</h2>


<p style="overflow:auto;height:300px">
 <ul id="msg"></ul>
</p>

<select id="users" class="form-control" style="max-width:150px;">
 <option value="0">所有人</option>
</select>

<input type="text" onkeydown=&#39;if (event.keyCode == 13) { $("#btn-send").click() }&#39; class="form-control" id="txt-msg" placeholder="内容" style="max-width:400px;" />
<br />
<button type="button" id="btn-send">发送</button>

/// <summary>
 /// 主动发送给用户消息，单例模式
 /// </summary>
 public class GroupChat
 {
 /// <summary>
 /// Clients，用来主动发送消息
 /// </summary>
 private IHubConnectionContext<dynamic> Clients { get; set; }

 private readonly static GroupChat _instance = new GroupChat(GlobalHost.ConnectionManager.GetHubContext<GroupChatHub>().Clients);

 private GroupChat(IHubConnectionContext<dynamic> clients)
 {
  Clients = clients;
 }

 public static GroupChat Instance
 {
  get
  {
  return _instance;
  }
 }


 /// <summary>
 /// 主动给所有人发送消息，系统直接调用
 /// </summary>
 /// <param name="msg"></param>
 public void SendSystemMsg(string msg)
 {
  Clients.All.publshMsg(new { Name = "系统消息", Msg = msg, Time = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") });
 }
 }