Why can I not save preferences on Android?

Question

I'm using the code in this tutorial (Full LibGDX game tutorial). The code to save the preferences works fine on Desktop but not on Android. Here's how I access and save my preferences:

public class AppPreferences {
private static final String PREF_MUSIC_VOLUME = "volume";
private static final String PREF_MUSIC_ENABLED = "music.enabled";
private static final String PREF_SOUND_ENABLED = "sound.enabled";
private static final String PREF_SOUND_VOL = "sound";
private static final String PREFS_NAME = "b2dtut";

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 float getMusicVolume() {
    return getPrefs().getFloat(PREF_MUSIC_VOLUME, 0.5f);
}

public void setMusicVolume(float volume) {
    getPrefs().putFloat(PREF_MUSIC_VOLUME, volume);
    getPrefs().flush();
}

public float getSoundVolume() {
    return getPrefs().getFloat(PREF_SOUND_VOL, 0.5f);
}

public void setSoundVolume(float volume) {
    getPrefs().putFloat(PREF_SOUND_VOL, volume);
    getPrefs().flush();
}
}

Answer 1

On Android, for some reason you have to store the reference to the Preferences object instead of accessing it using Gdx.app.getPreferences(PREFS_NAME). It probably has to do with how Android's built-in preferences work and how getPreferences interracts with it but I am unsure of the exact reason why. To solve this simply make this change:

private Preferences preferences;

protected Preferences getPrefs() {
    if (preferences == null)
        preferences = Gdx.app.getPreferences(PREFS_NAME);
    return preferences;
}