public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        StartListening();
    }

    private void button2_Click(object sender, EventArgs e)
    {
        StopListening();
    }

    private const string SERVER = "localhost";
    private const string DATABASE = "testdb";
    private const string USER = "postgres";
    private const string PASSWORD = "postgres";

    static string GetConnectionString()
    {
        var csb = new NpgsqlConnectionStringBuilder
        {
            Host = SERVER,
            Database = DATABASE,
            Username = USER,
            Password = PASSWORD
            //, Syncnotification = true
        };
        return csb.ConnectionString;
    }

    static NpgsqlConnection _notificationConnection;
    static void StartListening()
    {
        _notificationConnection =
           new NpgsqlConnection(GetConnectionString());
        _notificationConnection.Open();

        string sql = "listen mynotification";

        using (NpgsqlCommand command = new NpgsqlCommand(sql,
           _notificationConnection))
        {
            command.ExecuteNonQuery();
        }

        _notificationConnection.Notification +=
           PostgresNotification;
    }

    static void StopListening()
    {
        string sql = "unlisten mynotification";

        _notificationConnection.Notification -=
           PostgresNotification;

        using (NpgsqlCommand command = new NpgsqlCommand(sql,
           _notificationConnection))
        {
            command.ExecuteNonQuery();
        }

        _notificationConnection.Close();
    }

    static int notifications = 0;
    static void PostgresNotification(object sender,
       NpgsqlNotificationEventArgs e)
    {
        Console.WriteLine("-------Notification {0} -->", notifications++);
        Console.WriteLine("  DATA {0}", e.AdditionalInformation);
        Console.WriteLine("  CHANNEL {0}", e.Condition);
        Console.WriteLine("  PID {0}", e.PID);
    }

    static void TriggerNotification()
    {
        try
        {
            string sql = @"notify mynotification, 'This is some extra data:" + notifications.ToString() + @"'";

            using (NpgsqlCommand command = new NpgsqlCommand(sql,
           _notificationConnection))
            {
                command.ExecuteNonQuery();
            }
        }
        catch (Exception x)
        {
            Console.WriteLine("{0}", x.ToString());
        }
    }
    private void button5_Click(object sender, EventArgs e)
    {
        TriggerNotification();
    }
}

private static void Check(Object stateInfo)
        {
            try
            {
                string sql = @"select 1";

                using (NpgsqlCommand command = new NpgsqlCommand(sql, _notificationConnection))
                {
                    command.ExecuteNonQuery();
                }
            }
            catch (Exception x)
            {
                Console.WriteLine("{0}", x.ToString());
            }
        }