Question

我正在尝试列出应用程序中产品的类别，并且我正在使用提供程序包进行状态管理。在构建期间，即使列表不是空白，其显示的列表也为空，然后我添加了一个click事件以在列表正常工作时对其进行更新。我在启动画面期间调用getAllCategories()函数，并且vallCategoryList有值。

这是我的类别课程

class Category with ChangeNotifier{

  int catId;
  String catName;
  String catThumbnail;

  List<SetCategory> allCategoryList = [];


void  getAllCategories() async {
    String categoryUrl = 'https://app.ecwid.com/api/ccccccc';

    Response allCategory = await get(categoryUrl);

    print('getAllCategories');


    if (allCategory.statusCode == 200) {
      var categoryData = allCategory.body;

      int totalcount = jsonDecode(categoryData)['count'];

      if (allCategoryList.length != totalcount) {
        allCategoryList.clear();

        for (int i = 0; i < totalcount; i++) {
          allCategoryList.add(SetCategory(
            catId: jsonDecode(categoryData)['items'][i]['id'],
            catName: jsonDecode(categoryData)['items'][i]['name'],
            catThumbnail: jsonDecode(categoryData)['items'][i]['thumbnailUrl'],
          ));

        }

      }
    }
    print('allcategorylist length ${allCategoryList.length}');

    notifyListeners();
  }



}

class SetCategory {

  int catId;
  String catName;
  String catThumbnail;

  SetCategory(
      { this.catId, this.catName, this.catThumbnail});

}

我的屏幕代码

class HomeScreen extends StatefulWidget {
  static const String id = 'homeScreen';
//  static int reload = 0;



  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
 @override
  Widget build(BuildContext context) {

      final category = Provider.of<Category>(context);

    print('category length ${category.allCategoryList.length}'); // here it shows length as 0 even though it has a value of 16.

    return Row(
                children: <Widget>[
                  Padding(
                    padding: const EdgeInsets.all(8.0),
                    child: Text(
                      'Category ${category.allCategoryList.length}',
                      style: TextStyle(
                        color: Colors.black,
                        fontWeight: FontWeight.bold,
                        fontSize: 15.0,
                      ),
                      textAlign: TextAlign.start,
                    ),
                  ),

                  InkWell(
                                      onTap: () {

                                        category.getAllCategories();  // when i tap here this updates the list
                                        }),
                ],
              ),

Answer 1

您是否在小部件中使用了ChangeNotifierProvider，如图here

如果您只是使用Provider，它不会更新，而只是使后代可以访问该对象

Answer 2

通过添加Consumer来解决，更改后的代码如下

child: Consumer<Category>(
                        builder: (_,category,__){
                          return ListView.builder();
}

Flutter：`notifyListeners`不更新列表

2 个答案: