更改项目状态后如何更新列表？（颤动和提供者）

Question

我遇到这个问题：我有一个项目列表，每个项目都有一个最喜欢的状态，并且我有一个显示最喜欢的项目的页面。我希望页面在切换收藏夹状态时更新并删除非收藏夹项目。

尝试ChangeNotifierProxyProvider也没有成功，状态正在更改，但通知监听器不会更新主列表。setState我知道应用程序中间有一个空的技巧只是为了触发刷新，但我知道有一个更简洁的涉及 Provider 的方法，但我不知道。

这是代码（我让它尽可能短）

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (context) => Collection(),
      builder: (context, child) => MaterialApp(
        home: MyHomePage(),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final _list = Provider.of<Collection>(context).favItems;

    return Scaffold(
      appBar: AppBar(
        title: Text("Test"),
      ),
      body: Container(
        child: ListView.builder(
          itemCount: _list.length,
          itemBuilder: (_, index) => ChangeNotifierProvider.value(
            value: _list[index],
            child: CardWidget(),
          ),
        ),
      ),
    );
  }
}

class CardWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final _item = Provider.of<Items>(context);

    return Card(
      child: Row(
        children: <Widget>[
          Text(_item.name),
          IconButton(
              icon:
                  _item.favourite ? Icon(Icons.star) : Icon(Icons.star_border),
              onPressed: () {
                _item.toggleFavourite();
              })
        ],
      ),
    );
  }
}

class Collection with ChangeNotifier {
  List<Items> _items = [
    Items(name: "a", favourite: true),
    Items(name: "b", favourite: true),
    Items(name: "c", favourite: true),
  ];

  List<Items> get favItems =>
      [..._items].where((element) => element.favourite == true).toList();
}

class Items with ChangeNotifier {
  String name;
  bool favourite;

  Items({this.name, this.favourite});

  toggleFavourite() {
    favourite = !favourite;
    notifyListeners();
  }
}

Answer 1

老实说，Provider 的工作方式是通过将数据沿着 widget 树从父级传播到子级，但是您希望子级 ( Item) 通知父级更改 ( Collection) ，这将使父级和子级相互依赖（并且会导致稍后一些意大利面条代码）。如果对收藏夹的每次更改都会更新列表，那么最好保留整个逻辑Collection并将类保留Item为简单模型

class Collection with ChangeNotifier {
  List<Items> _items = [
    Items(name: "a", favourite: true),
    Items(name: "b", favourite: true),
    Items(name: "c", favourite: true),
  ];

  List<Items> get favItems =>
      [..._items].where((element) => element.favourite == true).toList();

  toggleFavourite(Item item) {
    int index = _items.indexWhere((element) => element.name == item.name);
    _items[index].favourite = !_items[index].favourite;
    notifyListeners();
  }
}

class Items { //simple Model class
  String name;
  bool favourite;

  Items({this.name, this.favourite});
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final _list = context.select((Collection list) => list.favItems); 
    //to update only if list is different

    return Scaffold(
      appBar: AppBar(
        title: Text("Test"),
      ),
      body: Container(
        child: ListView.builder(
          itemCount: _list.length,
          itemBuilder: (_, index) => CardWidget(_list[index])
        ),
      ),
    );
  }
}

class CardWidget extends StatelessWidget {
  final Item _item;

  CardWidget(this._item);

  @override
  Widget build(BuildContext context) {
    return Card(
      child: Row(
        children: <Widget>[
          Text(_item.name),
          IconButton(
              icon:
                  _item.favourite ? Icon(Icons.star) : Icon(Icons.star_border),
              onPressed: () {
                Provider.of<Collection>(context, listen: false).toggleFavourite(_item);
              })
        ],
      ),
    );
  }
}