code: protected void changeTheme() {
          currentTheme = getNextTheme(currentTheme);
          if (currentTheme != null) {
              currentTheme.setLooping(false);
              currentTheme.setOnCompletionListener(listener);
              currentTheme.setVolume(musicVolume.getPercent());
              currentTheme.play();
          }
      }
docs: Forces a change of current theme. Assumes a theme was already played - there are no smooth fade ins of any
  kind.