Flutter pagination

pagination_example.dart

class Pagination<T> {
  Pagination({
    this.page,
    this.perPage,
    this.total,
    this.totalPages,
    this.collection,
  });

  int page;
  int perPage;
  int total;
  int totalPages;
  List<T> collection;
}

abstract class PaginationModel<T> {
  PaginationModel({
    this.currentPage = 1,
    this.pageSize = 25,
    this.pagination,
  });

  int currentPage;
  int pageSize;
  Pagination<T> pagination;
  List<T> get items => pagination?.collection ?? <T>[];

  void initialize() {
    pagination = Pagination<T>(collection: <T>[]);
    currentPage = 1;
    pageSize = 25;
  }

  Future<void> fetchData();

  void updateWith(Pagination<T> pagination) {
    if (pagination != null) {
      if (pagination?.collection?.isNotEmpty ?? false) {
        this.pagination.collection.addAll(pagination.collection);
      }

      this.pagination.page = pagination.page ?? this.pagination.page;
      this.pagination.perPage = pagination.perPage ?? this.pagination.perPage;
      this.pagination.total = pagination.total ?? this.pagination.total;
      this.pagination.totalPages =
          pagination.totalPages ?? this.pagination.totalPages;
    }
  }

  Future<void> handleItemCreated(int index) async {
    final itemPosition = index + 2;
    final canFetchMoreData = itemPosition % pageSize == 0 && itemPosition != 0;

    if (canFetchMoreData) {
      final pageToRequest = (itemPosition ~/ pageSize) + 1;

      if (pageToRequest > currentPage &&
          pageToRequest <= (pagination?.totalPages ?? 0)) {
        currentPage = pageToRequest;

        await fetchData();
      }
    }
  }
}