public MainWindow() : base(Gtk.WindowType.Toplevel) { Build(); string connectionString = "Server=localhost;Database=dbprueba;User Id=dbprueba;Password=sistemas"; ApplicationContext.Instance.DbConnection = new NpgsqlConnection(connectionString); dbConnection = ApplicationContext.Instance.DbConnection; dbConnection.Open(); IDbCommand dbCommand = dbConnection.CreateCommand(); dbCommand.CommandText = "select a.id, a.nombre, a.precio, c.nombre as categoria " + "from articulo a left join categoria c " + "on a.categoria = c.id"; IDataReader dataReader = dbCommand.ExecuteReader(); TreeViewExtensions.Fill(treeView, dataReader); dataReader.Close(); dataReader = dbCommand.ExecuteReader(); TreeViewExtensions.Fill(treeView, dataReader); dataReader.Close(); }