Install-Package Microsoft.AspNet.SignalR.SelfHost 

Install-Package Microsoft.Owin.Cors

using System; 
 
namespace Server 
{ 
 public class UserInfo 
 { 
  public string ConnectionId { get; set; } 
  public string UserName { get; set; } 
  public DateTime LastLoginTime { get; set; } 
 } 
}

using Microsoft.AspNet.SignalR;
using Microsoft.AspNet.SignalR.Hubs;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Server
{
 [HubName("IMHub")]
 public class ChatHub : Hub
 {
  // 静态属性
  public static List<UserInfo> OnlineUsers = new List<UserInfo>(); // 在线用户列表

  /// <summary>
  /// 登录连线
  /// </summary>
  /// <param name="userId">用户Id</param>
  /// <param name="userName">用户名</param>
  public void Register(string userName)
  {
   var connnectId = Context.ConnectionId;

   if (OnlineUsers.Count(x => x.ConnectionId == connnectId) == 0)
   {
    if (OnlineUsers.Any(x => x.UserName == userName))
    {
     var items = OnlineUsers.Where(x => x.UserName == userName).ToList();
     foreach (var item in items)
     {
      Clients.AllExcept(connnectId).onUserDisconnected(item.ConnectionId, item.UserName);
     }
     OnlineUsers.RemoveAll(x => x.UserName == userName);
    }

    //添加在线人员
    OnlineUsers.Add(new UserInfo
    {
     ConnectionId = connnectId,
     UserName = userName,
     LastLoginTime = DateTime.Now
    });
   }

   // 所有客户端同步在线用户
   Clients.All.onConnected(connnectId, userName, OnlineUsers);
  }

  /// <summary>
  /// 发送私聊
  /// </summary>
  /// <param name="toUserId">接收方用户连接ID</param>
  /// <param name="message">内容</param>
  public void SendPrivateMessage(string toUserName, string message)
  {
   var fromConnectionId = Context.ConnectionId;

   var toUser = OnlineUsers.FirstOrDefault(x => x.UserName == toUserName);
   var fromUser = OnlineUsers.FirstOrDefault(x => x.ConnectionId == fromConnectionId);

   if (toUser != null )
   {
    Clients.Client(toUser.ConnectionId).receivePrivateMessage(fromUser.UserName, message);
    Clients.Client(toUser.ConnectionId).receivePrivateMessage(message);
   }
   else
   {
    //表示对方不在线
    Clients.Caller.absentSubscriber();
   }
  }

  public void Send(string name, string message)
  {
   //Clients.All { get; } // 代表所有客户端
   //Clients.AllExcept(params string[] excludeConnectionIds); // 除了参数中的所有客户端
   //Clients.Client(string connectionId); // 特定的客户端，这个方法也就是我们实现端对端聊天的关键
   //Clients.Clients(IList<string> connectionIds); // 参数中的客户端
   //Clients.Group(string groupName, params string[] excludeConnectionIds); // 指定客户端组，这个也是实现群聊的关键所在
   //Clients.Groups(IList<string> groupNames, params string[] excludeConnectionIds);参数中的客户端组
   //Clients.User(string userId); // 特定的用户
   //Clients.Users(IList<string> userIds); // 参数中的用户

   Console.WriteLine("ConnectionId:{0}, InvokeMethod:{1}", Context.ConnectionId, "Send");
   Clients.All.addMessage(name, message);
  }

  /// <summary>
  /// 连线时调用
  /// </summary>
  /// <returns></returns>
  public override Task OnConnected()
  {
   Console.WriteLine("客户端连接，连接ID是:{0},当前在线人数为{1}", Context.ConnectionId, OnlineUsers.Count+1);
   return base.OnConnected();
  }


  /// <summary>
  /// 断线时调用
  /// </summary>
  /// <param name="stopCalled"></param>
  /// <returns></returns>
  public override Task OnDisconnected(bool stopCalled)
  {
   var user = OnlineUsers.FirstOrDefault(u => u.ConnectionId == Context.ConnectionId);

   // 判断用户是否存在,存在则删除
   if (user == null)
   {
    return base.OnDisconnected(stopCalled);
   }

   Clients.All.onUserDisconnected(user.ConnectionId, user.UserName); //调用客户端用户离线通知
   // 删除用户
   OnlineUsers.Remove(user);
   Console.WriteLine("客户端断线，连接ID是:{0},当前在线人数为{1}", Context.ConnectionId, OnlineUsers.Count);
   return base.OnDisconnected(stopCalled);
  }

  public override Task OnReconnected()
  {
   return base.OnReconnected();
  }
 }
}

using Microsoft.Owin.Cors;
using Owin;

namespace Server
{
 public class Startup
 {
  public void Configuration(IAppBuilder app)
  {
   //允许CORS跨域
   app.UseCors(CorsOptions.AllowAll);
   app.MapSignalR();
  }
 }
}

using Microsoft.Owin.Hosting;
using System;

namespace Server
{
 class Program
 {
  static void Main(string[] args)
  {
   string url = "http://localhost:10086";//设定 SignalR Hub Server 对外的接口
   using (WebApp.Start(url))//启动 SignalR Hub Server
   {
    Console.WriteLine("Server running on {0}", url);
    Console.ReadLine();
   }
  }
 }
}