无论我做什么，C# SignalR 客户端都会抛出“如果连接不活动，则无法调用‘InvokeCoreAsync’方法”

Question

感觉我在这里失去了理智。

我的服务器的

Program.cs

包含以下行 -

builder.Services.AddSignalR();
app.MapHub<NotificationUserHub>("/NotificationUserHub");

NotificationUserHub

看起来像这样 -

public class NotificationUserHub : Hub<INotificationClient>
{
    private readonly IUsersStateContainer _container;
    public NotificationUserHub(IUsersStateContainer container) => _container = container;

    public async Task AddConnectionToGroup(string groupName)
    {
        var ctx = Context.ConnectionId;
        await Groups.AddToGroupAsync(Context.ConnectionId, groupName);
        _container.Update(ctx, groupName);
    }

    public async Task SendNotificationToUser(Notification message)
        => await Clients.Groups(message.To).ReceiveMessage(message);
    public override async Task OnDisconnectedAsync(Exception exception)
    {
        _container.Remove(Context.ConnectionId);
        await base.OnDisconnectedAsync(exception);
    }
}

我在 Blazor 客户端中的连接代码如下所示 -

var url = $"{WebApiOptions.Value.BaseUrl}NotificationUserHub";
Console.WriteLine($"Hub connection should be {url}");

_hubConnection = new HubConnectionBuilder()
    .WithUrl(url)
    .WithAutomaticReconnect()
    .Build();

_hubConnection.On<Notification>("ReceiveMessage", (message) =>
{
    _notificationMessage = message.Type switch
    {
        Enums.NotificationType.NewMessage => $"New message from {message.From}",
        Enums.NotificationType.ConversationClosed => $"Conversation closed by {message.From}",
        _ => string.Empty
    };

    PageInfo.SetUnreadMessageCount(message.UnreadCount);
    if (!string.IsNullOrEmpty(_notificationMessage))
    {
        MessageNotification.Show();
    }
});

try
{
    await _hubConnection.StartAsync();
    await _hubConnection.InvokeAsync("AddConnectionToGroup", PageInfo.CurrentUserEmail);
    hubInitialised = true;
}
catch (Exception ex)
{
    Console.WriteLine(ex.ToString());
}

正如您可能从问题标题中猜到的那样，无论我做什么，我都会在

'InvokeCoreAsync' method cannot be called if the connection is not active

行得到

InvokeAsync

，而我无法终生弄清楚为什么或如何。

Hub 方法

AddConnectionToGroup

永远不会被调用，Hub 状态表示在

InvokeAsync

之前已连接，之后已断开连接。

明显的罪魁祸首是连接 URL，但我已经检查过了，它是正确的。

非常感谢收到的任何建议。

Answer 1

当您调用

Start

方法时，您无法确定连接是否已建立并连接，如文档所述：

Start 是一个承诺，在连接建立后解决 成功建立，或因错误而拒绝。

所以我认为你需要检查连接状态：

protected override async Task OnInitializedAsync()
    {
        hubConnection = new HubConnectionBuilder()
            .WithUrl(Navigation.ToAbsoluteUri("/chathub"))
            .Build();

        hubConnection.On<string, string>("ReceiveMessage", (user, message) =>
        {
            var encodedMsg = $"{user}: {message}";
            messages.Add(encodedMsg);
            StateHasChanged();
        });

        await hubConnection.StartAsync();
    }

    private async Task Send()
    {
        if (hubConnection is not null)
            {
                await hubConnection.SendAsync("SendMessage", userInput, messageInput);
            }
    }
    
    // this is the method you need to check the connection state  <-------
    public bool IsConnected =>
        hubConnection?.State == HubConnectionState.Connected;

我从这里得到了这个代码：SignalR with Blazor