public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
   mLogger.info("saw pref key " + key);
   if (key.equals(SettingsActivity.KEY_BTC_UNITS)) {
     SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
     String btcUnits = sharedPref.getString(SettingsActivity.KEY_BTC_UNITS, "");
     setBTCUnits(btcUnits);
   }
 }
  @Override
  public void onCreate() {
    // Apply PRNGFixes.
    PRNGFixes.apply();

    initLogging();

    super.onCreate();

    // Log the About contents so we have the version string.
    mLogger.info(getResources().getString(R.string.about_contents));

    SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
    String btcUnits = sharedPref.getString(SettingsActivity.KEY_BTC_UNITS, "");
    setBTCUnits(btcUnits);

    // Register for future preference changes.
    sharedPref.registerOnSharedPreferenceChangeListener(this);

    mLogger.info("WalletApplication created");
  }