如何访问基本状态类中不存在的集体状态属性？

发布于 2025-02-05 03:44:08 字数 828 浏览 2 评论 0原文

考虑以下状态：

class ExerciseInitialState extends ExerciseState {}

class ExerciseLoadingState extends ExerciseState {}

class ExerciseLoadedState extends ExerciseState {
  final List<Data> data;

  const ExerciseLoadedState({required this.data});

  @override
  List<Object> get props => [data];

  // total count
  int get totalCount => data.length;
}

在UI中，我必须将状态（exropiseState）施加到ercoresEloAdedState，以便能够访问其属性，该属性在>中不存在练习载体和corameInitialState：

final total = (context.read<ExerciseBloc>().state as ExerciseLoadedState).totalCount

必须始终进行此操作对我来说似乎很尴尬。是将相同属性添加到基类exromisesestate的唯一解决方案？

原文

Consider these states:

class ExerciseInitialState extends ExerciseState {}

class ExerciseLoadingState extends ExerciseState {}

class ExerciseLoadedState extends ExerciseState {
  final List<Data> data;

  const ExerciseLoadedState({required this.data});

  @override
  List<Object> get props => [data];

  // total count
  int get totalCount => data.length;
}

In the UI, I have to cast the state (ExerciseState) to ExerciseLoadedState to be able to access its property which doesn't exist in the ExerciseLoadingState and ExerciseInitialState:

final total = (context.read<ExerciseBloc>().state as ExerciseLoadedState).totalCount

It looks awkward to me to have to do this casting all the time. Is the only solution to add the same properties to the base class ExerciseState?

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满栀 2025-02-12 03:44:09

它不应该对您感到不对 - 如果您希望该属性在所有州类中可用，则应在基类中定义。例如，您无法获得totalCount，而状态为erecoreSeloAdingState仅仅是因为此属性在此处未定义 - 您需要将类型推广到特定类型。

这个问题有两种可能的解决方案：

将类型提升为exromiseSeloAdedState访问属性：

return BlocBuilder<ExerciseBloc, ExerciseState>(
  builder: (context, state) {
    final totalCount = state is ExerciseLoadedState
        ? (state as ExerciseLoadedState).totalCount
        : 0;
  },
);

在ercorysestate上创建扩展方法：

extension ExerciseStateX on ExerciseState {
  int get totalCount => this is ExerciseLoadedState
      ? (this as ExerciseLoadedState).totalCount
      : 0;
}

使用扩展，您无需在UI层中进行类型促销。

It should not feel wrong to you - if you want the property to be available in all the state classes, it should be defined in the base class. E.g. you cannot get the totalCount while the state is ExerciseLoadingState simply because this property is not defined here - you need to promote the type to a specific one.

There are two possible solutions to this problem:

Promote the type to ExerciseLoadedState to access the property:

return BlocBuilder<ExerciseBloc, ExerciseState>(
  builder: (context, state) {
    final totalCount = state is ExerciseLoadedState
        ? (state as ExerciseLoadedState).totalCount
        : 0;
  },
);

Create an extension method on ExerciseState:

extension ExerciseStateX on ExerciseState {
  int get totalCount => this is ExerciseLoadedState
      ? (this as ExerciseLoadedState).totalCount
      : 0;
}

With the extension, you won't need to do the type promotion in your UI layer.

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