Uri path = Uri.parse("android.resource://com.mypackagename/"+R.raw.sound);
RingtoneManager.setActualDefaultRingtoneUri(getApplicationContext(), RingtoneManager.TYPE_RINGTONE,  path);

final String packageName = context.getPackageName();
    return Uri.parse("android.resource://" + packageName + "/"+R.raw.xxx);