Map got edited in a function without any return statement

Question

So strange behavior for me, I am so confused, I have been with these 3 hours and still don't get it.

Problem :

I am calling an instance from a provider withe name “idea” and later using that instance attribute in my widget.

This is my instance :

Widget build(BuildContext context) {
    var idea = Provider.of<Idea>(context, listen: false).allideas.firstWhere(
          (element) => element.id == widget.idea_id,
        );

then I am calling another provider to call two functions

• HTTP request

          final connectionData =
              await Provider.of<IdeaConnection>(context, listen: false)
                  .createIdeaConnection(
            idea.userId,
            idea.id,
          );
              final ideaProvider =
                  Provider.of<IdeaConnection>(context, listen: false);
              await ideaProvider.uppdeaIdeaConnectionsprov(
                idea.connections,
                connectionData,
              );
  

  Future<dynamic> createIdeaConnection(int resiver_user_id, int idea_id) async {
      final url = Uri.parse('http://10.0.2.2:3000/ideaconnetion');
      var jwt = await storage.read(key: "token");
      var userid = await storage.read(key: "id");
      var response;
      if (jwt != null) {
        final Map<String, String> tokenData = {
          "Content-Type": "application/json",
          "token": jwt
        };
        try {
          response = await http.post(url,
              headers: tokenData,
              body: json.encode({
                "resiver_user_id": resiver_user_id,
                "idea_id": idea_id,
              }));
          response = jsonDecode(response.body);
        } catch (error) {
          print(error);
          rethrow;
        }
      }
      return response;
    }
  

• calling another function to update data locally

  Future<void> uppdeaIdeaConnectionsprov(
      Map<int, IdeaConnectionsModel> connections, data) async {
    var id = await storage.read(key: "id") as String;
    var userData = await getLogedinUserData();
    connections.putIfAbsent(
        data['user_id'],
        () => IdeaConnectionsModel(
              id: data['id'],
              uppdatedAtt: DateTime.parse(data['updatedAt']),
              fName: userData['fName'] as String,
              imge: stringToByteList(userData['image']!),
              lNmae: userData['lName'] as String,
              userId: int.parse(id),
              userName: userData['userName'] as String,
              accepted: false,
              idea_Id: data['idea_id'],
            ));
  }
  

What is strange is that the uppdeaIdeaConnectionsprov() do not return any map, but the map I am sending to the function gets updated and i see changes in my Text widget how is this possible......

> Text(
>                             "${idea.connections.length}  Connections",
>                             style: const TextStyle(
>                                 color: Colors.white,
>                                 fontWeight: FontWeight.bold,
>                                 fontSize: 12),
>                           ),

Answer 1

As stated in the documentation, putIfAbsent() modifies the current map. If you want the current map to remain unchanged and get a new map with new values, you can clone the existing map and call putIfAbsent() on the new map.

Future<Map<int, IdeaConnectionsModel>> uppdeaIdeaConnectionsprov(
    Map<int, IdeaConnectionsModel> connections, data) async {
  var id = await storage.read(key: "id") as String;
  var userData = await getLogedinUserData();
  
  return Map<int, IdeaConnectionsModel>.from(connections)..putIfAbsent(
      data['user_id'],
          () => IdeaConnectionsModel(
        id: data['id'],
        uppdatedAtt: DateTime.parse(data['updatedAt']),
        fName: userData['fName'] as String,
        imge: stringToByteList(userData['image']!),
        lNmae: userData['lName'] as String,
        userId: int.parse(id),
        userName: userData['userName'] as String,
        accepted: false,
        idea_Id: data['idea_id'],
      ));
}