Flutter：参数类型“对象？” 不能分配给参数类型 'Map<string, dynamic> '</string,>

Question

我刚刚尝试从 firebase 获取消息，但它说 DocumentSnapShot 返回 Object，我的 ModelMessage.fromJson 希望它是 Map<String, dynamic>..

FirebaseFirestore firestore = FirebaseFirestore.instance;

  Stream<List<MessageModel>> getMessagesByUserId(int userId) {
    try {
      return firestore
          .collection('messages')
          .where('userId', isEqualTo: userId)
          .snapshots()
          .map((QuerySnapshot list) {
        var result = list.docs.map<MessageModel>((DocumentSnapshot message) {
          

          return MessageModel.fromJson(message.data()); <--- the error is here (message.data())

        }).toList();

       
        result.sort(
          (MessageModel a, MessageModel b) =>
              a.createdAt.compareTo(b.createdAt),
        );

        return result;
      });
    } catch (e) {
      throw Exception(e);
    }
  }

有什么方法可以将 object 转换为动态字符串，或者我的代码有问题吗？..谢谢

Answer 1

尝试这个

 return MessageModel.fromJson(message.data() as Map<String, dynamic>);