Can't pass in a subtype of an abstract class as argument into a function

Question

I followed the BloC tutorial and did according to them, I have a Bloc which has this method

  @override Stream<FridgeState> mapEventToState(FridgeEvent event) async* { .. }

where FridgeEvent is an abstract class

abstract class FridgeEvent {
  const FridgeEvent();
}

class CreateFridgeEvent extends FridgeEvent {
  final double lat, lng;

  CreateFridgeEvent({required this.lat, required this.lng});
}

class DeleteFridgeEvent extends FridgeEvent {}

When instantiating the bloc within the widget and passing in a subclass of FridgeEvent, I get an error that the parameter type can't be assigned. What am I doing wrong?

Upon request, here's the code of the bloc

import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:foodey_flutter/domain/fridge/entity/Fridge.dart';
import 'package:foodey_flutter/domain/fridge/usecase/CreateFridgeUseCase.dart';
import 'package:foodey_flutter/factory/FridgeFactory.dart';
import 'package:foodey_flutter/ui/fridge/create//event.dart';
import 'package:foodey_flutter/ui/fridge/create//state.dart';

class FridgeBloc extends Bloc<FridgeEvent, FridgeState> {
  CreateFridgeUseCase? createFridgeUseCase;

  FridgeBloc(FridgeState initialState) : super(initialState) {
    FridgeFactory.inject(this);
  }

  @override
  Stream<FridgeState> mapEventToState(FridgeEvent event) async* {
    if (event is CreateFridgeEvent) {
      Fridge? result = await createFridgeUseCase?.execute(event.lat, event.lng);
      if (result != null)
        yield FridgeSuccessfullyLoadedState(result);
      else
        yield FridgeErrorState(
            exception: Exception("Failed to create a fridge"));
    } else {
      yield FridgeErrorState(exception: Exception("Operation not supported"));
    }
  }
}

Here's the code of the widget

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:foodey_flutter/ui/fridge/create/FridgeBloc.dart';
import 'package:foodey_flutter/ui/fridge/create/event.dart';

class CreateFridgeWidget extends StatefulWidget {
  @override
  _CreateFridgeState createState() => _CreateFridgeState();
}

class _CreateFridgeState extends State<CreateFridgeWidget> {
  late FridgeBloc _bloc;

  @override
  void initState() {
    super.initState();
    this._bloc = BlocProvider.of<FridgeBloc>(context);
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      key: widget.key,
      alignment: Alignment.center,
      padding: EdgeInsets.all(8),
      child: Column(
        children: [
          Text("Are you sure you want to create your fridge?"),
          Row(
            children: [
              TextButton(
                key: widget.key,
                onPressed: () {
                  _bloc.add(CreateFridgeEvent(lat: 0, lng: 1));
                },
                child: Text("Yes"),
              ),
              TextButton(
                key: widget.key,
                onPressed: () => {},
                child: Text("No"),
              ),
            ],
          )
        ],
      ),
    );
  }
}

And here are my defined events

abstract class FridgeEvent {
  const FridgeEvent();
}

class CreateFridgeEvent extends FridgeEvent {
  final double lat, lng;

  CreateFridgeEvent({required this.lat, required this.lng});
}

class DeleteFridgeEvent extends FridgeEvent {}

Update: After copy pasting the code here and checking for completeness I found the issue. For anyone facing the same: the import of the event within the bloc code contains two /'s within the path. After removing one / the compiler didn't complain anymore that the wrong type is being passed. No idea how this second / was added and why the compiler didn't complain at all about that. Apparently, the objects defined in ..//event.dart are not the same when imported from ../event.dart

Solution

After copy pasting the code here and checking for completeness I found the issue. For anyone facing the same: the import of the event within the bloc code contains two /'s within the path. After removing one / the compiler didn't complain anymore that the wrong type is being passed. No idea how this second / was added and why the compiler didn't complain at all about that. Apparently, the objects defined in ..//event.dart are not the same when imported from ../event.dart

Comments

[Kirill Bubochkin]

Can be a problem with imports. Can you share your bloc file and widget file (full code with imports)?

[nvoigt]

Pleas provide a minimal reproducible example.

[Martin Nowosad]

updated, thanks for the hint