flutter - 在运行时未设置值，但在热重启后设置了值

Question

我有以下情况:FutureBuilder方法中有一个build:

FutureBuilder<List>(
            future: NutritionDataManager().getDishes(),
            initialData: List(),
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                List<Dish> dishes = snapshot.data.map((dish) {
                  return Dish(dish.id, dish.icon, dish.name, dish.gram, dish.calories, dish.time);
                }).toList();
                countTotalCalories(dishes);
                return SliverList(
                  delegate: SliverChildBuilderDelegate(
                    (BuildContext context, int index) {
                      return NutritionListItemWidget(
                        dish: snapshot.data[index],
                      );
                    },
                    childCount: snapshot.data.length,
                  ),
                );
              } else {
                return Container();
              }
            },
          )

这个 future 将从数据库中获取数据，如果获取了数据(snapshot.hasData)，它将调用一个方法，该方法将基于此数据进行计算:

countTotalCalories(List<Dish> dishes) {
    int calSum = 0;
    dishes.forEach((dish) => calSum += dish.calories);    
    _currentCalories = calSum;        
  }

然后在另一个Widget中使用此值( _currentCalories)。但是，当我运行我的应用程序时， _currentCalories总是得到零值，但是当我按热重启时，一切正常。那么，这个问题怎么了，我该如何解决呢？提前致谢!

UPD

这是我屏幕的整个代码:

class NutritionScreen extends StatefulWidget {
  const NutritionScreen({Key key}) : super(key: key);

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

class _NutritionScreenState extends State<NutritionScreen> {
  int _currentCalories = 0;

  @override
  Widget build(BuildContext context) {
    var date = "Aug 27";

    return Scaffold(
      backgroundColor: Color(AppColors.white),
      floatingActionButton: FloatingActionButton(
        backgroundColor: Color(AppColors.brandViolet),
        onPressed: () => showModalBottomSheet(
          context: context,
          isScrollControlled: true,
          builder: (context) => BottomNutritionModal(),
        ),
        child: Icon(Icons.add),
      ),
      body: SafeArea(
        child: CustomScrollView(slivers: <Widget>[
          SliverAppBar(
            title: Padding(
              padding: const EdgeInsets.only(right: 50.0),
              child: Center(child: Text(date, style: TextStyle(color: Colors.black))),
            ),
            backgroundColor: Colors.white,
            floating: true,
            automaticallyImplyLeading: true,
            leading: IconButton(
              icon: Icon(Icons.close, color: Colors.black),
              onPressed: () => Navigator.pop(context, false),
            ),
            elevation: 0,
          ),
          SliverPersistentHeader(
            delegate: _SliverPersistentHeaderDelegate(
              child: PreferredSize(
                preferredSize: Size.fromHeight(MediaQuery.of(context).size.height * 0.4),
                child: LayoutBuilder(builder: (BuildContext context, BoxConstraints constraints) {
                  return Container(
                    color: Colors.white,
                    child: Column(
                      children: <Widget>[
                        RichText(
                          textAlign: TextAlign.center,
                          text: TextSpan(
                            style: TextStyle(color: Colors.black, fontSize: Dimensions.boldTextSize, fontWeight: FontWeight.bold),
                            children: <TextSpan>[
                              TextSpan(text: "You have consumed \n"),
                              TextSpan(text: "500 out of 1900 cal", style: TextStyle(color: Color(AppColors.brandViolet))),
                            ],
                          ),
                        ),
                        Padding(
                          padding: const EdgeInsets.only(top: 10.0),
                          child: AnimatedCircularChart(
                            size: Size(constraints.maxHeight / 1.3, constraints.maxHeight / 1.3),
                            initialChartData: <CircularStackEntry>[
                              CircularStackEntry(
                                <CircularSegmentEntry>[
                                  CircularSegmentEntry(33.33, Color(AppColors.brandViolet)),
                                  CircularSegmentEntry(66.67, Color(AppColors.layoutBackgroundColor)),
                                ],
                              ),
                            ],
                            chartType: CircularChartType.Radial,
                            edgeStyle: SegmentEdgeStyle.round,
                            percentageValues: true,
                            holeLabel: "$_currentCalories",
                            labelStyle: new TextStyle(
                              color: Colors.blueGrey[600],
                              fontWeight: FontWeight.bold,
                              fontSize: 35,
                            ),
                          ),
                        )
                      ],
                    ),
                  );
                }),
              ),
            ),
          ),
          FutureBuilder<List>(
            future: NutritionDataManager().getDishes(),
            initialData: List(),
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                List<Dish> dishes = snapshot.data.map((dish) {
                  return Dish(dish.id, dish.icon, dish.name, dish.gram, dish.calories, dish.time);
                }).toList();
                countTotalCalories(dishes);
                return SliverList(
                  delegate: SliverChildBuilderDelegate(
                    (BuildContext context, int index) {
                      return NutritionListItemWidget(
                        dish: snapshot.data[index],
                      );
                    },
                    childCount: snapshot.data.length,
                  ),
                );
              } else {
                return Container();
              }
            },
          )
        ]),
      ),
      // bottomNavigationBar: SafeArea(child: NutritionBottomInputWidget()),
    );
  }

  countTotalCalories(List<Dish> dishes) {
    int calSum = 0;
    dishes.forEach((dish) => calSum += dish.calories);
    setState(() {
      _currentCalories = calSum;
    });
  }
}

Answer 1

使用以下代码可能会对您有所帮助。将_currentCalories放在setState方法中。

 countTotalCalories(List<Dish> dishes) {
  int calSum = 0;
  dishes.forEach((dish) => calSum += dish.calories);
  if (mounted){
    setState(() {
      _currentCalories = calSum;
    });
  }
}