波动类别提供者中列表始终为空

Question

我正在使用provider程序包进行扑打。

问题是我有一个get方法，在此方法下我返回了an instance of categories list array

但是由于某些原因，即使通过API向其中添加数据之后，该列表也始终为空。

下面是代码：

import 'package:flutter/material.dart';
import '../configs/api_contants.dart';
import '../models/category_model.dart';
import '../models/product_model.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

class CategoriesProvider with ChangeNotifier{
  List<Category> _items = [];
  int currentPage = 1;
  int lastPage = 1;

  List<Category> get items {
    print("Items askfor are : $_items");
    return [..._items];
  }

  Category findById(String id) {
    return _items.firstWhere((cat) => cat.id == id);
  }

  Future<void> fetchCategories() async {
    try {
      final response = await http.get(categoriesApi);
      final data = json.decode(response.body) as Map<String, dynamic>;
      final categories = data['data'];
      if(categories == null) {
       return [...items];
      }

      categories.forEach((prodData){
        var img = (prodData['attributes']['image_url']!= null) ? imgBaseUrl+prodData['attributes']['image_url'] : 'http://placehold.it/1200x1200';
        try {
          print(prodData);
          print('--------------------');
          _items.add(
            Category(
              id: prodData['id'].toString(),
              name: prodData['attributes']['name'],
              imgUrl: img,
            )
          );
        } catch (e) {
          print(e);
        }
      });
      notifyListeners();
    } catch (e) {
      print(e);
    }
  }
}

您会看到有一个print statement，它确实显示了API的记录列表。

_items.add()是我正在使用的东西，到目前为止，我还没有error那个东西。

代码哪里出错了？

如果我在_items.add()之后添加打印，也会在控制台中得到以下输出。

flutter: Instance of 'Future<void>'
flutter: Items askfor are : []
flutter: []
flutter: --------------------
flutter: [Instance of 'Category']
flutter: --------------------
flutter: [Instance of 'Category', Instance of 'Category']
flutter: --------------------
flutter: [Instance of 'Category', Instance of 'Category', Instance of 'Category']
flutter: --------------------
flutter: [Instance of 'Category', Instance of 'Category', Instance of 'Category', Instance of 'Category']
flutter: Items askfor are : []