SignalR 向同一用户发送重复消息 n 次 n 是连接的用户数 .NetCore

如何解决SignalR 向同一用户发送重复消息 n 次 n 是连接的用户数 .NetCore

我有 SignalR ASP.NET Core 项目，并尝试向特定用户发送消息，我设法这样做了。问题是相同的消息发送 n 时间 n=number 的选项卡或连接，当数据库发生更改时，它会向该特定用户发送通知，但会重复该消息。

public class MessageHub: Hub
{       
    public MessageHub(IConfiguration cc,IHubContext<MessageHub> _mess,UserManager<ApplicationUser> rep)
    {
        mess = _mess;
        _conf = cc;
        _usermanager = rep;
        RegisterNotification();
    }

    public void RegisterNotification()
    {        
        using (sqlConnection con = new sqlConnection(conStr))
        {
            sqlCommand cmd = new sqlCommand(sqlCommand,con);

            if (con.State != System.Data.ConnectionState.Open)
            {
                con.open();
            }

            cmd.Notification = null;
        
            sqlDependency sqlDep = new sqlDependency(cmd);
          
            sqlDep.OnChange += sqlDep_OnChange;
          
            using (sqlDataReader reader = cmd.ExecuteReader())
            {
                // nothing need to add here Now
            }
        }
    }

    static int count = 1;
    private  void sqlDep_OnChange(object sender,sqlNotificationEventArgs e)
    {
        if (e.Type == sqlNotificationType.Change )
        {
            sqlDependency sqlDep = sender as sqlDependency;
            sqlDep.OnChange -= sqlDep_OnChange;
                      
            mess.Clients.User("64ed09d7-255f-4aae-a25f-7a50e59943b4").SendAsync("abc","hello"+count);
            count += 1;

           RegisterNotification();
        }
    }
}

解决方法

正如您所提到的，问题是每次创建 RegisterNotification 实例时都会调用 MessageHub。取而代之的是，您可以创建后台服务并在那里注册到 SqlDependency 并使用 IHubContext 发送事件。每次通知后，您再次调用 RegisterNotification，这也可能导致重复。

• https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services
• https://docs.microsoft.com/en-us/aspnet/core/signalr/hubcontext

我还没有测试过这段代码，但这里有一个例子：

public class EventBroadcaster : IHostedService
{
    private readonly IHubContext<MessageHub> _hubContext;
    private readonly string _connectionString;

    public EventBroadcaster(
           IConfiguration configuration,IHubContext<MessageHub> hubContext)
    {
         _hubContext = hubContext;
         _connectionString = // Get Connection String from configuration
    }

    public Task StartAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("Started event broadcasting service");

        RegisterNotification();
        return Task.CompletedTask;
    }


    public void RegisterNotification()
    {        
        using (SqlConnection con = new SqlConnection(_connectionString))
        {
            SqlCommand cmd = new SqlCommand(sqlCommand,con);

            if (con.State != System.Data.ConnectionState.Open)
            {
                con.Open();
            }

            cmd.Notification = null;
        
            SqlDependency sqlDep = new SqlDependency(cmd);
          
            sqlDep.OnChange += sqlDep_OnChange;
          
            using (SqlDataReader reader = cmd.ExecuteReader())
            {
                // nothing need to add here now
            }
        }
    }

    static int count = 1;
    private async void sqlDep_OnChange(object sender,SqlNotificationEventArgs e)
    {
        if (e.Type == SqlNotificationType.Change )
        {
            SqlDependency sqlDep = sender as SqlDependency;
            sqlDep.OnChange -= sqlDep_OnChange;
                      
            await _hubContext.Clients.User("64ed09d7-255f-4aae-a25f-7a50e59943b4").SendAsync("abc","hello"+count);

            count += 1;
        }
    }

    public Task StopAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("Event Broadcasting Service is stopping.");

        // TODO: Stop listening to SqlDependency notifications

        return Task.CompletedTask;
    }