so i am trying to add a new object to activity and i store it in local storage, the code looks like this

 pushObjectWisata(selectedIndex, selectedObjectId) async {

    PengunjungModel dataObjectWisata = listObjectWisata
        .firstWhere((element) => element.id == selectedObjectId);


    listAktifitas[selectedIndex].dataAktifitas!.add(dataObjectWisata);

    await saveListAktifitas(listAktifitas);
  }

but i got this error:

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Converting object to an encodable object failed: Instance of ‘listActivities’.

listAktifitas it self is a list with multilevel object. the model look like this

import ‘dart:convert’;

import ‘package:sbh_v2/model/pariwisata/pengunjung_model.dart’;

class listActivities {
  String? namaAktifitas;
  int? statusAktifitas;
  int? countActivity;
  String? thumbnail;
  List<PengunjungModel>? dataAktifitas;

  listActivities({
    this.namaAktifitas,
    this.statusAktifitas,
    this.countActivity,
    this.thumbnail,
    this.dataAktifitas,
  });

  factory listActivities.fromJson(Map<String, dynamic> json) => listActivities(
        namaAktifitas: json['namaAktifitas'].toString(),
        countActivity: json['countActivity'],
        statusAktifitas: json['statusAktifitas'],
        thumbnail: json['thumbnail'].toString(),
        dataAktifitas: List<PengunjungModel>.generate(
          json['dataAktifitas'].length,
          (index) => PengunjungModel.fromJson(
              json['dataAktifitas'][index] ?? <String, dynamic>{}),
        ),
      );

  static List<listActivities> fromJsonList(dynamic jsonList) {
    final listAktifitas = <listActivities>[];
    if (jsonList == null) return listAktifitas;

    if (jsonList is List<dynamic>) {
      for (final json in jsonList) {
        listAktifitas.add(
          listActivities.fromJson(json),
        );
      }
    }

    return listAktifitas;
  }

  factory listActivities.fromRawJson(String str) =>
      listActivities.fromJson(jsonDecode(str));

  String toRawJson() => jsonEncode(toJson());

  Map<String, dynamic> toJson() {
    final data = <String, dynamic>{};
    data['namaAktifitas'] = namaAktifitas;
    data['statusAktifitas'] = statusAktifitas;
    data['countActivity'] = countActivity;
    data['thumbnail'] = thumbnail;
    data['dataAktifitas'] = dataAktifitas;
    return data;
  }
}

as you can see, it has relation to another list which is pengungungModel List. and the model look like this:

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:sbh_v2/model/pariwisata/foto.dart';
import 'package:sbh_v2/model/pariwisata/kategori_pengunjung.dart';

class PengunjungModel {
  String? title;
  int? id;
  String? harga_terendah;
  String? harga_tertinggi;
  String? deskripsi;
  String? jam_buka;
  String? jam_tutup;
  String? alamat;
  String? fasilitas;
  double? lat;
  double? lng;
  List<Foto>? list_foto = <Foto>[];
  KategoriPengunjung? kategoriPengunjung;

  PengunjungModel(
      {this.id,
      this.title,
      this.harga_terendah,
      this.harga_tertinggi,
      this.deskripsi,
      this.alamat,
      this.list_foto,
      this.jam_tutup,
      this.jam_buka,
      this.fasilitas,
      this.lat,
      this.lng,
      this.kategoriPengunjung});

  factory PengunjungModel.fromJson(Map<String, dynamic> json) =>
      PengunjungModel(
        id: json['id'],
        title: json['title'] ?? "-",
        alamat: json['alamat'] ?? "-",
        jam_buka: json['jam_buka'] ?? "-",
        jam_tutup: json['jam_tutup'] ?? "-",
        fasilitas: json['fasilitas'],
        lat: double.parse(json['lat'] ?? '0'),
        lng: double.parse(json['lng'] ?? '0'),
        harga_terendah: json['harga_terendah'] ?? "",
        harga_tertinggi: json['harga_tertinggi'] ?? "",
        deskripsi: json['deskripsi'] ?? "-",
        list_foto: List<Foto>.generate(
          json['foto'].length,
          (index) => Foto.formJson(
            json['foto'][index] ?? <String, dynamic>{},
          ),
        ),
        kategoriPengunjung: KategoriPengunjung.fromJson(
            json['kategori_layanan_pengunjung'] ?? <String, dynamic>{}),
      );

  factory PengunjungModel.fromRawJson(String str) =>
      PengunjungModel.fromJson(jsonDecode(str));
}

basically i tried to add an object of pengunjungModel data with spesic id to a listAktifitas with specific index…

in pushObjectWisata i tried to print the selectedIndex and selectedObjectId and it works fine. but when i tried to print the dataObjectWisata it return that error and the same thing happen when i add the dataObjectWisata to listAktivitas.

i dont know what i dont understand. but maybe this is because of the model of those two..

please help me…. thank you