using System.Collections.Generic;
using System.Threading.Tasks;
using Microsoft.AspNetCore.SignalR;

namespace NetCoreWebApi.SignalR
{
    /// 

    /// Message集线器
    /// 
    public class MessageHub : Hub
    {
        /// 

        /// 存放已连接信息
        /// 
        public static readonly Dictionarystring, string> Connections = new Dictionarystring, string>();
        /// 

        /// 发送消息
        /// 
        /// 
        /// 
        /// 
        public async Task SendMessage(string loginNo, string message)
        {
            Connections.TryGetValue(loginNo, out string clientId);
            //ReceiveMessage 客户端接受方法
            await Clients.Client(clientId).SendAsync("ReceiveMessage", message);
        }
        /// 

        /// 客户端登录成功保存用户账号和客户端Id
        /// 
        /// 
        public void SendLogin(string loginNo)
        {
            //判断用户有没有登陆过(没登陆过插入用户名和Id，登陆过修改用户名和Id)
            if (!Connections.ContainsKey(loginNo))
            {
                Connections.Add(loginNo, Context.ConnectionId);
            }
            else
            {
                Connections[loginNo] = Context.ConnectionId;
            }
        }
    }
}

            services.AddSignalR();

            //设置SignalR路由,指向自定义类MessageHub
            app.UseSignalR(route =>
            {
                route.MapHub("/MessageHub");
            });

DOCTYPE HTML>
html>
head>
head>
body>
    div style="text-align: center;margin-top: 5%">
        input type="text" id="message" placeholder="消息" />
        button type="button" id="sendBtn">发送button>
    div>
    script src="../Resources/lib/signalr/dist/browser/signalr.js">script>
body>
html>
script>
    var connection = new signalR.HubConnectionBuilder()
        //配置路由
        .withUrl("/MessageHub")
        //日志信息
        .configureLogging(signalR.LogLevel.Information)
        //创建
        .build();
    //接受消息
    connection.on("ReceiveMessage", (message) => {
        alert("收到消息===>" + message);
    });
    //发送消息
    document.getElementById("sendBtn").addEventListener("click", function () {
        var message = document.getElementById(‘message‘).value;
        connection.invoke("SendMessage", "tenghao510@qq.com", message).catch(err =>
            console.error(err.toString())
        );
    });
    //开始连接
    connection.start().then(e => {
        connection.invoke("SendLogin", "tenghao510@qq.com").catch(err =>
            console.error(err.toString())
        );
    }).catch(err => console.error(err.toString()));
script>

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.SignalR;
using NetCoreWebApi.SignalR;

namespace NetCoreWebApi.Controllers
{
    /// 

    /// SignalR推送
    /// 
    [Route("api/hub")]
    [ApiController]
    public class HubController : Controller
    {
        private readonly IHubContext _hubContext;
        /// 

        /// 构造函数
        /// 
        /// 
        public HubController(IHubContext hubClients)
        {
            _hubContext = hubClients;
        }
        /// 

        /// 测试SignalR推送
        /// 
        /// 
        [HttpGet]
        [Route("pushMsg")]
        public void PushMsg(string loginNo)
        {
            if (string.IsNullOrWhiteSpace(loginNo))
            {
                //给所有人推送消息
                _hubContext.Clients.All.SendAsync("ReceiveMessage", "这是控制器发送的消息");
            }
            else
            {
                //给指定人推送
                MessageHub.Connections.TryGetValue(loginNo, out string id);
                _hubContext.Clients.Client(id).SendAsync("ReceiveMessage", "这是控制器发送的消息");
            }
        }
    }
}