Why are the elements removed on booth Lists?

Question

Why does it remove the list element from booth lists?
Is it in Darts just a pointer?
How to fix it?

class _ResultsState extends State<Results> {
    var _league;
    var originalLeague;

    @override
    void initState() {
        super.initState();
        _league = API_Manager.getLeagueFull(widget.leagueId, widget.seasonId, context);
    }

    void filterData(String teamName) async {
        if (originalLeague == null) {
          _league = await _league;
          originalLeague = List.from(_league);
        }
        List<LeagueModel> leagues = List.from(originalLeague);

        print('List length: ${originalLeague[0].dates.length}');

        if (teamName != 'Kein Filter') {
          leagues[0].dates.removeWhere((element) => !element.guestTeam.contains(teamName) && !element.homeTeam.contains(teamName));
        }

        print('List length now: ${originalLeague[0].dates.length}');
        print('New List length: ${leagues[0].dates.length}');

        setState(() {
          _league = filteredList(leagues);
        });
    }

    Future<List<LeagueModel>> filteredList( List<LeagueModel> list) async {
        return list;
    }
 }

Console Output:

flutter: List length: 30
flutter: List length now: 10
flutter: New List length: 10

Edit:
As recommendet i testet [...data] and List.from(data) but it still removes the elements from booth lists. Updated the code above

Answer 1

It about instance, try newList = [...oldList] or newList = List.from(oldList).

Example: