getHistoryMessages method Null safety

Future<List> getHistoryMessages({@required dynamic type, @required int? from, @required int? limit, bool isDescend = false})

批量获取本地历史消息

@param target 聊天对象， JMSingle | JMGroup @param from 起始位置 @param limit 获取数量 @param isDescend 是否倒叙

Implementation

Future<List> getHistoryMessages(
    {@required dynamic type,

    /// (JMSingle | JMGroup)
    @required int? from,
    @required int? limit,
    bool isDescend = false}) async {
  Map param = type.toJson();

  param..addAll({'from': from, 'limit': limit, 'isDescend': isDescend});

  List resArr = await _channel.invokeMethod('getHistoryMessages',
      param..removeWhere((key, value) => value == null));

  List res = [];
  for (Map messageMap in resArr) {
    dynamic d = JMNormalMessage.generateMessageFromJson(messageMap);
    if (d != null) {
      res.add(d);
    } else {
      print("get history msg, get a message is null");
    }
  }
  //var res = resArr.map((messageMap) => JMNormalMessage.generateMessageFromJson(messageMap)).toList();
  return res;
}