Flutter BLoC 8.0.0无法正常发射新状态问题排查

在Flutter中使用BLoC 8.0.0版本处理UI事件，通过ToggleButtons让用户切换三个按钮，选中不同按钮时从数据库返回对应实体列表展示。实体包含bool isSale和bool isClosed参数，三个按钮对应布尔组合：

• 按钮1：isSale = true, isClosed = false
• 按钮2：isSale = true, isClosed = true
• 按钮3：isSale = false, isClosed = false

目前发现第二种组合无法更新到新状态，相关代码如下：

状态类定义 #

abstract class DocViewerState extends Equatable {
  const DocViewerState();
}

class DocViewerLoadingState extends DocViewerState {
  @override
  List<Object> get props => [];
}

class DocViewerLoadedState extends DocViewerState {
  bool isSale;
  bool isClosed;
  int? selectedIndex;

  DocViewerLoadedState({required this.isSale, required this.isClosed, required this.selectedIndex});
  @override
  List<Object> get props => [isSale, isClosed];
}

事件类定义 #

abstract class DocViewerEvent extends Equatable {
  const DocViewerEvent();
}

class ModeChangedEvent extends DocViewerEvent {
  bool isSale;
  bool isClosed;

  ModeChangedEvent({required this.isSale, required this.isClosed});
  @override
  List<Object?> get props => [isSale, isClosed];
}

事件处理函数 #

void _onModeChanged(ModeChangedEvent event, Emitter<DocViewerState> emit) {
  emit(DocViewerLoadingState());
  this.isSale = event.isSale;
  this.isClosed = event.isClosed; // 用于外部搜索流
  try {
    emit(DocViewerLoadedState(
      isClosed: event.isClosed,
      isSale: event.isSale,
      selectedIndex: null,
    )); // 仅第一种和第三种组合的emit生效
  } catch (e) {
    print(e); /// 未捕获到异常
  }
  print(event.isSale); 
  print(event.isClosed);
  print(state);
}

打印结果显示参数传递正确，但第二种组合的状态停留在DocViewerLoadingState()：

• 第一种组合：

I/flutter ( 5019): true
I/flutter ( 5019): false
I/flutter ( 5019): DocViewerLoadedState(true, false)

• 第二种组合：

I/flutter ( 5019): true
I/flutter ( 5019): true
I/flutter ( 5019): DocViewerLoadingState()

• 第三种组合：

I/flutter ( 5019): false
I/flutter ( 5019): false
I/flutter ( 5019): DocViewerLoadedState(false, false)

核心问题出在Equatable的props配置不完整以及BLoC的状态比较逻辑：

1. DocViewerLoadedState的props只包含了isSale和isClosed，未纳入selectedIndex。如果之前的状态中selectedIndex不为null，当新状态传入selectedIndex: null时，Equatable会认为两个状态的props相同（仅比较isSale和isClosed），导致BLoC跳过状态更新。
2. 第二种组合的isSale=true, isClosed=true刚好命中上述场景：历史状态中存在相同的isSale和isClosed组合，且selectedIndex的变化未被纳入比较，导致emit(DocViewerLoadedState)被BLoC忽略，最终状态停留在之前的DocViewerLoadingState。

1. 完善DocViewerLoadedState的props配置 #

将selectedIndex加入props列表，确保状态的所有可变属性都参与Equatable的相等性比较：

class DocViewerLoadedState extends DocViewerState {
  bool isSale;
  bool isClosed;
  int? selectedIndex;

  DocViewerLoadedState({required this.isSale, required this.isClosed, required this.selectedIndex});
  @override
  List<Object?> get props => [isSale, isClosed, selectedIndex];
}

2. 确保状态类的不可变性（可选但推荐） #

BLoC的状态类应保持不可变性，将属性改为final：

class DocViewerLoadedState extends DocViewerState {
  final bool isSale;
  final bool isClosed;
  final int? selectedIndex;

  const DocViewerLoadedState({required this.isSale, required this.isClosed, required this.selectedIndex});
  @override
  List<Object?> get props => [isSale, isClosed, selectedIndex];
}

3. 验证状态更新逻辑 #

在事件处理函数中打印状态的相等性，确认新状态与当前状态的差异：

void _onModeChanged(ModeChangedEvent event, Emitter<DocViewerState> emit) {
  emit(DocViewerLoadingState());
  this.isSale = event.isSale;
  this.isClosed = event.isClosed;
  try {
    final newLoadedState = DocViewerLoadedState(
      isClosed: event.isClosed,
      isSale: event.isSale,
      selectedIndex: null,
    );
    print('New state equals current state? ${newLoadedState == state}');
    emit(newLoadedState);
  } catch (e) {
    print(e);
  }
  print(event.isSale); 
  print(event.isClosed);
  print(state);
}

内容的提问来源于stack exchange，提问作者dalibro