使用CTRL + F5刷新页面时出现错误，计时器工作两次，并使用signalR在布局上推送通知

Question

这是前端代码：

var chat = $.connection.chatHub;
$.connection.hub.start().done(function () {
    chat.server.start();
});
chat.client.addNewMessageToPage = function (username) {
    alertify.success(name + message);
};

$.connection.hub.disconnected(function () {
    setTimeout(function () { $.connection.hub.start(); }, 1000);
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

首次加载页面时，此方法有效，但是刷新页面时，计时器和警报提示似乎运行两次。

这是后端代码：

namespace DHPGROUP
{
    public class ChatHub : Hub
    {
        private Timer timer = new Timer();
        private static readonly ConcurrentDictionary<string, UserHubModels> Users = new ConcurrentDictionary<string, UserHubModels>(StringComparer.InvariantCultureIgnoreCase);

        private void start()
        {
            timer.Interval = 15000;
            timer.Elapsed += Tim_Elapsed2;
            timer.Start();
        }

        private void Tim_Elapsed2(object sender, ElapsedEventArgs e)
        {
            PublicChatHub pubChatHub = new PublicChatHub();


            Clients.All.addNewMessageToPage(pubChatHub.GetCalls());

        }

        public override Task OnConnected()
        {
            string userName = Context.User.Identity.Name;
            string connectionId = Context.ConnectionId;
            var user = Users.GetOrAdd(userName, _ => new UserHubModels
            {
                UserName = userName,
                ConnectionIds = new HashSet<string>()
            });
            lock (user.ConnectionIds)
            {
                user.ConnectionIds.Add(connectionId);
                if (user.ConnectionIds.Count == 1)
                {
                    Clients.Others.userConnected(userName);
                    start();
                }
            }
            return base.OnConnected();
        }

        public override Task OnDisconnected(bool stopCalled)
        {
            string userName = Context.User.Identity.Name;
            string connectionId = Context.ConnectionId;
            UserHubModels user;
            Users.TryGetValue(userName, out user);
            if (user != null)
            {
                lock (user.ConnectionIds)
                {
                    user.ConnectionIds.RemoveWhere(cid => cid.Equals(connectionId));
                    if (!user.ConnectionIds.Any())
                    {
                        UserHubModels removedUser;
                        Users.TryRemove(userName, out removedUser);
                        Clients.Others.userDisconnected(userName);
                        timer.Enabled = false;
                        timer.Stop();
                        timer.Dispose();
                    }
                }
            }

            return base.OnDisconnected(stopCalled);
        }

    }

    public class UserHubModels
    {
        public string UserName { get; set; }
        public HashSet<string> ConnectionIds { get; set; }
    }


    public class PublicChatHub
    {
        private readonly IUnitOfWork _unitOfWork = new UnitOfWork(new ApplicationDbContext());
        public List<CallViewModel> GetCalls()
        {
            try
            {
                var currentDateTime = DateTime.Now;
                var queryCallViewModel = _unitOfWork.CallRepository.AsQueryable()
                    .Where(tr => !tr.Accomplished)
                    .Where(rt => rt.DateTimeStartUtc >= currentDateTime && rt.DateTimeEndUtc <= currentDateTime)
                    .Select(er => new CallViewModel
                    {
                        Id = er.Id,
                        Caption = er.Caption,
                    }).ToList();
                return queryCallViewModel;
            }
            catch (Exception)
            {
                throw;
            }
        }
    }
}