按下后图标没有改变 - Flutter

Question

我正在创建收藏页面。对于每个产品页面，我在应用栏上放置了一个喜欢的图标，该图标可以更改并将特定产品添加到用户的收藏夹中。

按下图标后无法更改图标状态。

class FoodDetail extends StatefulWidget {
  @override
  _FoodDetail createState()=> _FoodDetail();

  const FoodDetail({Key key}) : super(key: key);

}
  
  class _FoodDetail extends State<FoodDetail>{

  @override
  Widget build(BuildContext context) {
    FoodNotifier foodNotifier = Provider.of<FoodNotifier>(context);

    _onFoodDeleted(Food food) {
      Navigator.pop(context);
      foodNotifier.deleteFood(food);
    }
  final _saved = Set<BuildContext>();
  final alreadySaved = _saved.contains(context);

    return Scaffold(
      appBar: AppBar(
        title: Text(foodNotifier.currentFood.name),
        actions: <Widget>[
          // action button
                    new IconButton(
                    icon: alreadySaved ? Icon(Icons.star) : Icon(Icons.star_border),
                    color: alreadySaved ? Colors.yellow[500] : null,
                    onPressed: (){
                      setState(() {
                      if (alreadySaved) {
                        _saved.remove(context);
                        } else {
                        _saved.add(context); 
                        }
                      });}

Answer 1

您的状态不会改变，因为您将它们放在 build 方法中，该方法总是会重新初始化它们。

将您的状态 _saved、alreadySaved 放在 build 方法之外。

  final _saved = Set<BuildContext>();
  final alreadySaved = _saved.contains(context);

  @override
  Widget build(BuildContext context) {

  }

按下后图标没有改变 - Flutter

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