Android SharedPreferences保存第一次的信息

   private void setHomeTimeZone() {
        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
        String homeTimeZone = prefs.getString(SettingsActivity.KEY_HOME_TZ, "");
        if (!homeTimeZone.isEmpty()) {
            return;
        }
        homeTimeZone = TimeZone.getDefault().getID();
        SharedPreferences.Editor editor = prefs.edit();
        editor.putString(SettingsActivity.KEY_HOME_TZ, homeTimeZone);
        editor.apply();
        Log.v(LOG_TAG, "Setting home time zone to " + homeTimeZone);
    }