I’m new to Flutter. I’m confused. If there is any mistake, please correct me.

Here, I’m using Provider and FutureBuilder. When “+” is pressed, it will add to the item in the provider. If the same “+” is pressed, it will add its quantity in the provider.

I hope that when I open this page again, the quantity value will still be there for each corresponding item. So in buildButtonCart, I added this:

Widget buildButtonCart({required LayananModel value}) {
  return Consumer<ItemCollectionProvider>(
    builder: (_, val, __) {
      return InputQty.int(
        ...
        initVal: val.getJumlah(value: value),
        ...
        onQtyChanged: (_) {
          val.add(value: value, jumlah: _);
        },
      );
    },
  );
}

But the result is still 0, this image:

https://drive.google.com/file/d/1ntOqxEFfqdKflOhIegeMuwpuLTpFYVo2/view?usp=sharing

Sorry I can’t upload the image, because when uploading, it always fails.

When I search, the result is the same, which is still 0. And, when I go back and open it again, the result is still 0. I’ve checked it by debugging in the provider. The data has been saved.

Am I implementing this wrong?

Here I attach some of the code needed:

PilihLayananPage.dart:

class _PilihLayananPageState extends State<PilihLayananPage> {
  bool _match = false;
  late Future<List<LayananModel>> _future;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: buildHeader(),
      body: buildLayout(),
    );
  }

  @override
  void initState() {
    super.initState();
    _future = LayananRepository.all(equal: false, limit: 30);
  }

  AppBar buildHeader() {
    return AppBar(
      title: Text("Pilih Layanan"),
    );
  }

  Widget buildLayout() {
    ...
  }

  Widget buildMatch() {
    ...
  }

  FutureBuilder<List<LayananModel>> buildFutureBuilderCollection() {
    return FutureBuilder<List<LayananModel>>(
      future: _future,
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.done) {
          if (snapshot.hasError) {
            return Center(
              child: Text(snapshot.error.toString()),
            );
          }

          if (snapshot.hasData && snapshot.data!.isEmpty) {
            return Center(
              child: Text("Data kosong"),
            );
          }

          if (snapshot.hasData && snapshot.data!.isNotEmpty) {
            List<LayananModel> daftarLayanan = snapshot.data!;

            return ListView.separated(
              separatorBuilder: (context, index) => Divider(),
              itemBuilder: (context, index) {
                LayananModel layanan = daftarLayanan[index];
                return ListTile(
                  title: Text(layanan.nama),
                  subtitle: Text(layanan.deskripsi),
                  trailing: buildButtonCart(value: daftarLayanan[index]),
                );
              },
              itemCount: snapshot.data!.length,
            );
          }
        }
        return Center(
          child: CircularProgressIndicator(),
        );
      },
    );
  }


  FutureBuilder<List<LayananModel>> buildFutureBuilderSearch() {
    return FutureBuilder<List<LayananModel>>(
      future: _future,
      builder: (context, snapshot) {
        return SearchBar(
          ...
          onSubmitted: (value) {
            setState(() {
              _future = LayananRepository.all(
                query: value,
                limit: 15,
                equal: _match,
              );
            });
          },
        );
      },
    );
  }

  Widget buildButtonCart({required LayananModel value}) {
    return Consumer<ItemCollectionProvider>(
      builder: (_, val, __) {
        return InputQty.int(
          ...
          initVal: val.getJumlah(value: value),
          ...
          onQtyChanged: (_) {
            val.add(value: value, jumlah: _);
          },
        );
      },
    );
  }
}

ItemProvider.dart

import 'dart:collection';

import 'package:flutter/material.dart';
import 'package:londri/models/item_model.dart';
import 'package:londri/models/layanan_model.dart';

class ItemCollectionProvider extends ChangeNotifier {
  final List<ItemModel> _daftarItem = [];

  UnmodifiableListView<ItemModel> get daftarItem =>
      UnmodifiableListView(_daftarItem);

  void add({required LayananModel value, required int jumlah}) {
    if (_isDuplicate(value: value)) {
      _countJumlah(value: value, jumlah: jumlah);
    } else {
      _daftarItem.add(_getItemObjectFrom(value: value));
    }
    notifyListeners();
  }

  ItemModel getItem({required LayananModel value}) {
    return _daftarItem[_getIndex(value: value)];
  }

  int getJumlah({required LayananModel value}) {
    try {
      return _daftarItem[_getIndex(value: value)].jumlah;
    } catch (error) {
      return 0;
    }
  }

  ItemModel _getItemObjectFrom({required LayananModel value}) {
    return ItemModel(
      itemId: 0,
      layananId: value.layananId,
      terimaId: 0,
      nama: value.nama,
      deskripsi: value.deskripsi,
      jumlah: 0,
    );
  }

  bool _isDuplicate({required LayananModel value}) {
    for (final _ in _daftarItem) {
      if (_.layananId == value.layananId) {
        return true;
      }
    }
    return false;
  }

  int _getIndex({required LayananModel value}) {
    int result =
        _daftarItem.indexWhere((val) => val.layananId == value.layananId);
    print(result);
    return result;
  }

  void _countJumlah({required LayananModel value, required int jumlah}) {
    int index = _getIndex(value: value);
    if (_daftarItem[index].jumlah <= 0) {
      /// Remove item here
      _daftarItem.removeAt(index);
    } else {
      _daftarItem[index].jumlah = jumlah;
    }
  }

  void removeAll() {
    _daftarItem.clear();
  }
}