顶级目录：/frameworks/base/packages/SettingsProvider/

步骤一

修改文件：res/values/defaults.xml

+     <integer name="def_ui_night_mode">2</integer>
</resources>

步骤二

修改文件：src/com/android/providers/settings/DatabaseHelper.java

private void loadSecureSettings(SQLiteDatabase db) {
         * See: SettingsProvider.UpgradeController#onUpgradeLocked
         */
+		loadIntegerSetting(stmt, Settings.Secure.UI_NIGHT_MODE, R.integer.def_ui_night_mode);
    } finally {
        if (stmt != null) stmt.close();
    }
}