var ips = Dns.GetHostAddressesAsync(Dns.GetHostName());

foreach (var ip in ips.Result)
{
    switch (ip.AddressFamily)
    {
        case AddressFamily.InterNetwork:
           TxbServer.Text = ip.ToString();
           break;
        case AddressFamily.InterNetworkV6:
           break;
     }
}

private Action<string> _updateListBoxAction;


//Определено в методе загрузки
//При наличии более 1000 фрагментов данных автоматически удаляем первый
//Когда появляется полоса прокрутки, она автоматически перемещается вниз
_updateListBoxAction = new Action<string>((s) =>
{
    listBox1.Items.Add(s);
    if (listBox1.Items.Count > 1000)
    {
        listBox1.Items.RemoveAt(0);
    }
    var visibleItems = listBox1.ClientRectangle.Height/listBox1.ItemHeight;

    listBox1.TopIndex = listBox1.Items.Count - visibleItems + 1;
});


//Добавляем ключевое событие и очищаем список при нажатии c
listBox1.KeyPress += (o, args) =>
{
    if (args.KeyChar == 'c' || args.KeyChar=='C')
    {
         listBox1.Items.Clear();
    }
};

        private async void MqttServer()
        {
            if (null != _mqttServer)
            {
                return;
            }

            var optionBuilder =
                new MqttServerOptionsBuilder().WithConnectionBacklog(1000).WithDefaultEndpointPort(Convert.ToInt32(TxbPort.Text));

            if (!TxbServer.Text.IsNullOrEmpty())
            {
                optionBuilder.WithDefaultEndpointBoundIPAddress(IPAddress.Parse(TxbServer.Text));
            }
            
            var options = optionBuilder.Build();
            
            
            (options as MqttServerOptions).ConnectionValidator += context =>
            {
                if (context.ClientId.Length < 10)
                {
                    context.ReturnCode = MqttConnectReturnCode.ConnectionRefusedIdentifierRejected;
                    return;
                }
                if (!context.Username.Equals("admin"))
                {
                    context.ReturnCode = MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
                    return;
                }
                if (!context.Password.Equals("public"))
                {
                    context.ReturnCode = MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
                    return;
                }
                context.ReturnCode = MqttConnectReturnCode.ConnectionAccepted;
                
            };
            

            _mqttServer = new MqttFactory().CreateMqttServer();
            _mqttServer.ClientConnected += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, $">Client Connected:ClientId:{args.ClientId},ProtocalVersion:");

                var s = _mqttServer.GetClientSessionsStatusAsync();
                label3.BeginInvoke(new Action(() => { label3.Text = $"Общее количество соединений: {s.Result.Count}"; }));
            };

            _mqttServer.ClientDisconnected += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, $"<Client DisConnected:ClientId:{args.ClientId}");
                var s = _mqttServer.GetClientSessionsStatusAsync();
                label3.BeginInvoke(new Action(() => { label3.Text = $"Общее количество соединений: {s.Result.Count}"; }));
            };

            _mqttServer.ApplicationMessageReceived += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction,
                    $"ClientId:{args.ClientId} Topic:{args.ApplicationMessage.Topic} Payload:{Encoding.UTF8.GetString(args.ApplicationMessage.Payload)} QualityOfServiceLevel:{args.ApplicationMessage.QualityOfServiceLevel}");

            };

            _mqttServer.ClientSubscribedTopic += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, $"@ClientSubscribedTopic ClientId:{args.ClientId} Topic:{args.TopicFilter.Topic} QualityOfServiceLevel:{args.TopicFilter.QualityOfServiceLevel}");
            };
            _mqttServer.ClientUnsubscribedTopic += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, $"%ClientUnsubscribedTopic ClientId:{args.ClientId} Topic:{args.TopicFilter.Length}");
            };

            _mqttServer.Started += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, "Mqtt Server Start...");
            };

            _mqttServer.Stopped += (sender, args) =>
            {
                listBox1.BeginInvoke(_updateListBoxAction, "Mqtt Server Stop...");
                
            };

            await _mqttServer.StartAsync(options);
        }