Flutter 块状态未正确更新

Question

I'm experiencing an issue, that my state isn't updating and I can't find the problem in my code.

Basically I'm updating my state like this :

Bloc

  @override
  WorkoutState get initialState => WorkoutsLoaded(
      workouts: ["Workout1", "Workout2", "Workout3"], selectedWorkoutIndex: 0);

  @override
  Stream<WorkoutState> mapEventToState(WorkoutEvent event) async* {
    if (event is UpdateWorkoutPageIndex) {
      yield* _mapUpdateWorkoutPageIndexToState(event);
    }

    if (event is IncreaseWorkoutPageIndex) {
      yield* _mapIncreaseWorkoutPageIndexToState(event);
    }

    if (event is DecreaseWorkoutPageIndex) {
      yield* _mapDecreaseWorkoutPageIndexToState(event);
    }
  }

  Stream<WorkoutState> _mapUpdateWorkoutPageIndexToState(
      UpdateWorkoutPageIndex event) async* {
    print("_mapUpdateWorkoutPageIndexToState : " + this.state.toString());
    yield WorkoutsLoaded(
        workouts: ["Workout0", "Workout2", "Workout3"],
        selectedWorkoutIndex: event.pageIndex);
    print("_mapUpdateWorkoutPageIndexToState End : " + this.state.toString());
  }

Event

class UpdateWorkoutPageIndex extends WorkoutEvent {
  final int pageIndex;

  const UpdateWorkoutPageIndex({@required this.pageIndex});

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

  @override
  String toString() => "UpdateWorkoutPageIndex { pageIndex: $pageIndex }";
}

State

class WorkoutsUninitialised extends WorkoutState {}

class WorkoutsLoaded extends WorkoutState {
  final List<String> workouts;
  final int selectedWorkoutIndex;

  const WorkoutsLoaded({
    this.workouts,
    this.selectedWorkoutIndex,
  });

  @override
  String toString() {
    return "WorkoutsLoaded : " + this.workouts.toString() + " - " + this.selectedWorkoutIndex.toString();
  }
}

The state doesn't change, even when the event.pageIndex is different.

I can provide further code if necessary, but currently I'm not sure what code could be needed to solve my issue.

Answer 1

if your WorkoutEvent Class extends equatable , Then you need to add this line

    List<Object> get props => [pageIndex]; 

to your UpdateWorkoutPageIndex class

The aim is that the [List] of props (properties) will be used to determine whether two [Equatables] are equal. Hence, state will be updated.