private void Skan_Click(object sender, RoutedEventArgs e)
        {
            DbClass.openConnection();

            DbClass.sql = "SELECT * FROM ksiazki WHERE id_ksiazki LIKE '" + usunid.Text + "';";
            DbClass.cmd.CommandType = CommandType.Text;
            DbClass.cmd.CommandText = DbClass.sql;

            DbClass.da = new SqlDataAdapter(DbClass.cmd);
            DbClass.dt = new DataTable();
            DbClass.da.Fill(DbClass.dt);

            myDatagrid2.ItemsSource = DbClass.dt.DefaultView;

            DbClass.closeConnection();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            CzyNaPewno Cnp = new CzyNaPewno(usunid.Text);
            Cnp.Show();
            this.Close();
        }