Pagination With StateNotifier

pagination_notifier.dart

import 'package:coves_management/notifiers/pagination/pagination_notifier_state.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:logging/logging.dart';

class PaginationNotifier<T> extends StateNotifier<PaginationNotifierState<T>> {
  PaginationNotifier({required this.fetchNextItems, required this.hitsPerPage})
      : super(const PaginationNotifierState.data([], false)) {
    init();
  }

  final Logger logger = Logger('PaginationNotifier');
  final Future<List<T>> Function(T? item, int offset,
      {String? query, required bool forceNetwork}) fetchNextItems;
  final int hitsPerPage;
  String _currentQuery = "";

  final List<T> _items = [];

  void init() {
    if (_items.isEmpty) {
      fetchNextPage();
    }
  }

  bool get _canLoadNextPage => state.maybeWhen(
        dataLoading: (_) => false,
        data: (_, hasReachedMax) => !hasReachedMax,
        orElse: () => true,
      );

  Future<void> loadQuery(String query) {
    _currentQuery = query;
    return fetchNextPage(skipLoadNextPageCheck: true, clearCurrentList: true);
  }

  Future<void> fetchNextPage(
      {bool skipLoadNextPageCheck = false,
      bool clearCurrentList = false,
      bool forceNetwork = false}) async {
    if (!mounted) {
      logger.warning("fetchNextPage called on unmounted PaginationNotifier");
      return;
    }
    if (!_canLoadNextPage && !skipLoadNextPageCheck) {
      return;
    }
    try {
      state = PaginationNotifierState.dataLoading(_items);
      final List<T> result = _items.isEmpty || clearCurrentList
          ? await fetchNextItems(null, 0,
              query: _currentQuery, forceNetwork: forceNetwork)
          : await fetchNextItems(_items.last, _items.length,
              query: _currentQuery, forceNetwork: forceNetwork);
      if (clearCurrentList) {
        _items.clear();
      }
      if (result.isEmpty) {
        state = PaginationNotifierState.data(_items, true);
      } else if (result.length < hitsPerPage) {
        state = PaginationNotifierState.data(_items..addAll(result), true);
      } else {
        state = PaginationNotifierState.data(_items..addAll(result), false);
      }
    } catch (e, stk) {
      print(mounted);
      state = PaginationNotifierState.error(e, stk);
    }
  }
}

/// Pagination State
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:freezed_annotation/freezed_annotation.dart';

part 'pagination_notifier_state.freezed.dart';

@freezed
abstract class PaginationNotifierState<T> with _$PaginationNotifierState<T> {
  const factory PaginationNotifierState.data(
      List<T> items, bool hasReachedMax) = _Data;
  const factory PaginationNotifierState.dataLoading(List<T> movies) =
      _DataLoading;
  const factory PaginationNotifierState.error(Object? e, [StackTrace? stk]) =
      _Error;
}

/// Controller listening to scrolling updates and fetching items if user reaches end of list
@override
  void initState() {
    super.initState();
    _invoiceScrollController = ScrollController();
    _invoiceScrollController.addListener(() {
      double maxScroll = _invoiceScrollController.position.maxScrollExtent;
      double currentScroll = _invoiceScrollController.position.pixels;
      double delta = MediaQuery.of(context).size.width * 0.20;
      if (maxScroll - currentScroll <= delta) {
        widget.onEnd(lastItem);
      }
    });
  }