SignalR在強制頁面重繪后更新通知

我在我的 ASP.NET Core MVC 專案中使用 signalR 向用戶推送通知。我在這里研究了類似的問題，但它的解決方案并沒有解決我的問題。我使用了以下 Javascript/jQuery 參考：

<script type="text/javascript" src="../../js/UserPage/jquery-3.6.0.min.js"></script>
<script src="~/microsoft/signalr/dist/browser/signalr.js"></script>
<script src="~/js/message.js"></script>

message.js 如下：

var connection = new signalR.HubConnectionBuilder().withUrl("/Home/Messages").withAutomaticReconnect().build();
connection.start();

if (document.getElementById("sendBtn") != null) {
    document.getElementById("sendBtn").addEventListener("click", function () {
        var costCenter = $("#cost-center").val();
        connection.invoke("SendMessage", costCenter).catch(function (err) {
            return console.error(err);
        });
    });
}

集線器的代碼：

public class MessageHub : Hub
{
    //Dependency injections
    private readonly IUserRepository _userRepository;
    private readonly ICostCenterRepository _costcenterRepository;
    private readonly IHttpContextAccessor _httpContext;

    public MessageHub(IUserRepository userRepository, ICostCenterRepository costcenterRepository, IHttpContextAccessor httpContext)
    {
        _userRepository = userRepository;
        _costcenterRepository = costcenterRepository;
        _httpContext = httpContext;
    }
    public async Task SendMessage(string costCenter)
    {
        var HttpContext = _httpContext.HttpContext;
        string userId = _userRepository.GetUserIdByCostCenter(costCenter).ToString();
        string sender = HttpContext.Session.GetString("department");
        await Clients.User(userId).SendAsync("ReceiveMessage", sender);
    }
}

而且，主頁中的javascript代碼是：

<script>
    $(document).ready(function(){
            connection.on("ReceiveMessage", function (param) {
            if($('#badge-count').length){
                var currentMessageNum = parseInt($('#badge-count').text());
                $('#badge-count').text(currentMessageNum   1);
                $('.main-msg-list').prepend('<li><a  style="font-family: vazir !important" asp-controller="Messages" asp-action="Index" href="" id="msg-'  currentMessageNum   1  '">???? ???? ?? '  param  '</a></li>');
            }else{
                $('#badge-count').text('1');
            }
        });
    });
</script>

問題是通知在強制重繪 后更新。之后，通知作業正常并立即更新。我該如何解決？

uj5u.com熱心網友回復：

我通過對 Hub 代碼進行一些更改來解決此問題：

[Authorize]
public class MessageHub : Hub
{
    //Dependancy injections
    private readonly IUserRepository _userRepository;
    private readonly ICostCenterRepository _costcenterRepository;
    private readonly IHttpContextAccessor _httpContext;

    public MessageHub(IUserRepository userRepository, ICostCenterRepository costcenterRepository, IHttpContextAccessor httpContext)
    {
        _userRepository = userRepository;
        _costcenterRepository = costcenterRepository;
        _httpContext = httpContext;
    }
    //define a dictionary to store the userid.
    private static Dictionary<string, List<string>> NtoIdMappingTable = new Dictionary<string, List<string>>();

    public override async Task OnConnectedAsync()
    {
        var username = Context.User.Identity.Name;
        var userId = Context.UserIdentifier;
        List<string> userIds;

        //store the userid to the list.
        if (!NtoIdMappingTable.TryGetValue(username, out userIds))
        {
            userIds = new List<string>();
            userIds.Add(userId);

            NtoIdMappingTable.Add(username, userIds);
        }
        else
        {
            userIds.Add(userId);
        }

        await base.OnConnectedAsync();
    }

    public override async Task OnDisconnectedAsync(Exception exception)
    {
        var username = Context.User.Identity.Name;

        //remove userid from the List
        if (NtoIdMappingTable.ContainsKey(username))
        {
            NtoIdMappingTable.Remove(username);
        }
        await base.OnDisconnectedAsync(exception);
    }
    public async Task SendMessage(string costCenter)
    {
        var HttpContext = _httpContext.HttpContext;
        string username = _userRepository.GetUsernameByCostCenter(costCenter).ToString();
        var userId = NtoIdMappingTable.GetValueOrDefault(username);
        string sender = HttpContext.Session.GetString("department");
        await Clients.User(userId.FirstOrDefault()).SendAsync("ReceiveMessage", sender);
    }
}

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