扫描导航后对集体事件没有反应

Question

因此，我目前有2个屏幕，一个屏幕有一个按钮，当用户按下按钮时，将显示第二个屏幕。没有什么太复杂了...

第二个屏幕应对集团发送的内容，并从本质上显示来自该群体发出的状态的数据。 所有功能都很好，并且可以正确显示vairables

fixedExpenseTotal

和

variableExpenseTtoal

，直到我增强了集团以散发出额外的状态为止；

FetchedBalanceBoughtForwardState

。 现在看来，Vairables

fixedExpenseTotal

和

variableExpenseTtoal

没有被填充，它显示空字符串。似乎是，当我使bloc重新发射状态时（使用屏幕2上的临时按钮），小部件最初无法对状态做出反应，屏幕2上的小部件会正确地做出反应。因此，我很困惑为什么屏幕2上的小部件在加载窗口小部件时不会反应。...是因为在加载小部件之前已经发出了状态？值得仅将

balance

领域添加为国家的一部分，以降低复杂性（尽管我希望各州/事件像适合的状态一样松散耦合）？尽管放置了

FetchedExpendituresForCertainMonthState

语句，但我最初可以看到屏幕2加载时，它确实会摄取

print

。

这是我的集团：

FetchedBalanceBoughtForwardState

这是屏幕1中的按钮的ONTAP处理程序：

FetchedExpendituresForCertainMonthState

这是对屏幕2上的群体发出的状态反应的小部件：

  on<FetchForMonthExpenditureDefinitions>((event, emit) async {
    
    //...business logic here

    emit(FetchedExpendituresForCertainMonthState(
        expendituresWithinTheMonth, monthToTraverse));

    //Now we want to calculate the balance being bought forward from the previous month
    add(CalculateBalanceBoughtForwardEvent(expenditures, from));
  });

  on<CalculateBalanceBoughtForwardEvent>((event, emit) async {
    double balance = calculator.calculateBalanceBeingBoughtForward(event.expenditureDefinitions, event.dateOfBalanceBoughtForward);
    print('Sending the balance bought forward as $balance');
    emit(FetchedBalanceBoughtForwardState(balance));
  });

当您做到

TextButton(
  child: const Text('Finish!'),
  onPressed: () async {
    //Passing the context which contains the blocprovider to myApp
    context.read<FinanceBloc>().add(
        FetchForMonthExpenditureDefinitions(
            DateTime.now()));
    Navigator.of(context).push(MaterialPageRoute(
      builder: (_) => BlocProvider.value(
        value: BlocProvider.of<FinanceBloc>(context),
        child: MyApp(),
      ),
    ));
  },
)

时，先前发射的状态

return Container(
    width: MediaQuery.sizeOf(context).width,
      child: Container(
        padding: const EdgeInsets.symmetric(vertical: 10.0, horizontal: 10.0),
        decoration: BoxDecoration(
          borderRadius: BorderRadius.circular(16.0),
          color: Colors.grey,
        ),
        child: BlocBuilder<FinanceBloc, FinanceState>(
          buildWhen: (previous, current) => 
            previous != current && current is FetchedBalanceBoughtForwardState,
          builder: (context, balanceState) {
            double balanceBeingBoughtForward = balanceState is FetchedBalanceBoughtForwardState 
                ? balanceState.balanceBoughtForward 
                : 0.0;
                
        return BlocBuilder<FinanceBloc, FinanceState>(
          buildWhen: (previous, current) => 
            previous != current && current is FetchedExpendituresForCertainMonthState,
          builder: (context, expendituresState) {
            String fixedIncomeTotal = "";
            String fixedExpenseTotal = "";
            String variableExpenseTtoal = "";
            String variableIncomeTotla = "";
            
            if (expendituresState is FetchedExpendituresForCertainMonthState) {
              expenditures = expendituresState.expenditures.values
                  .expand((list) => list)
                  .toList();
              currentMonth = expendituresState.updatedDate;
              fixedIncomeTotal = getFixedIncome(expenditures).toString();
              fixedExpenseTotal = getFixedExpense(expenditures).toString();
              variableExpenseTtoal = getVariableExpense(expenditures).toString();
              variableIncomeTotla = getVariableIncome(expenditures).toString();
            }

            return Column(children: [
              Text("Overview of expenditures for this month",
                  style: const TextStyle(fontSize: 24)),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  Text("Total fixed income: £$fixedIncomeTotal"),
                  Text("Total fixed expense: £$fixedExpenseTotal")
                ]
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  Text("Total variable income: £$variableIncomeTotla"),
                  Text("Total variable expense: £$variableExpenseTtoal")
                ]
              ),
              Text("Balance bought forward: £$balanceBeingBoughtForward"),
              Text("Click here for more intel!"),
            ]);
          },
        );
      },
    ),
  ),
);

丢失了。由于locbuilder听到

Answer 1

是父母，因此它会触发重建，这也将触发儿童bloc的重建，因此现在if条件

FetchedExpendituresForCertainMonthState

为

FetchedBalanceBoughtForwardState

，因此值不会被填充。

最好的解决方案将仅使用一种状态并使用

expendituresState is FetchedExpendituresForCertainMonthState

发出新状态，以免丢失先前发射的状态值。另外，您应该尽量避免在任何地方筑巢

false

，因为它可能会产生意外的结果。

使用

freezed

用于集体状态。它将为您生成

copyWith

方法，也让您将状态设置回

BlocBuilder

。虽然，您可以使用自己的

copyWith

实施。