title: How correctly save game progress via libGDX Preferences on Android devices?
body: <p><strong>I am using next code.
  This code work fine on desktop version, but on Android device does not.
  return Gdx.app.getPreferences(PREFS_NAME) always is null.
  Why? Where I could make mistake?</strong></p>
  
  <pre><code>import com.badlogic.gdx.Gdx;
  import com.badlogic.gdx.Preferences;
  
  public class BeatlesPreferences {
      // constants
      private static final String PREF_VIBRO = "vibro";
      private static final String PREF_MUSIC_ENABLED = "musicenabled";
      private static final String PREF_SOUND_ENABLED = "soundenabled";
      private static final String PREFS_NAME = "my_app";
  
      public BeatlesPreferences() {
      }
  
      protected Preferences getPrefs() {
          return Gdx.app.getPreferences(PREFS_NAME);
      }
  
      public boolean isSoundEffectsEnabled() {
          return getPrefs().getBoolean(PREF_SOUND_ENABLED, true);
      }
  
      public void setSoundEffectsEnabled(boolean soundEffectsEnabled) {
          getPrefs().putBoolean(PREF_SOUND_ENABLED, soundEffectsEnabled);
          getPrefs().flush();
      }
  
      public boolean isMusicEnabled() {
          return getPrefs().getBoolean(PREF_MUSIC_ENABLED, true);
      }
  
      public void setMusicEnabled(boolean musicEnabled) {  
          getPrefs().putBoolean(PREF_MUSIC_ENABLED, musicEnabled);
          getPrefs().flush();
      }
  
      public boolean isVibroEnabled() {
          return getPrefs().getBoolean(PREF_VIBRO, true);
      }
  
      public void setVibroEnabled(boolean vibro) {
          getPrefs().putBoolean(PREF_VIBRO, vibro);
          getPrefs().flush();
      }
  }
  </code></pre>