Bloc: Migration guide to 5.0.0

[Zazo032]

Is your feature request related to a problem? Please describe.
Migration from 4.0.1 to 5.0.0

Describe the solution you'd like
Provide some steps for different use cases

The specific case is, we have some code like this:

class SampleBloc extends Bloc<SampleEvent, SampleState> {
  String data;

  @override
  SampleState get initialState {
    data = 'initial data';
    if (hasExtraData)
      data += 'extra data';
    return SampleState(data);
  }
}

However, there's no trivial change to migrate that code. We have successfully migrated other initialState where it just returns a state, to provide them to super the constructor of the class.

[felangel]

Hi @Zazo032 👋
Thanks for opening an issue!

I'm working on a formal migration guide and am aiming to have it published tomorrow. In the meantime for your use-case I would recommend the following:

class SampleBloc extends Bloc<SampleEvent, SampleState> {
  SampleBloc({String data = 'initial data', bool hasExtraData})
      : super(SampleState('$data ${hasExtraData ? 'extra data' : ''}'));
}

Let me know if that helps 👍

[narcodico]

Hi @Zazo032 👋

Another approach besides the one suggested by @felangel is:

class SampleBloc extends Bloc<SampleEvent, SampleState> {
  final String data;

  SampleBloc(this.data): super((){
    if (hasExtraData)
      data += 'extra data';
    return SampleState(data);
}());
}

[Zazo032]

Both of those solutions is giving me the following analyzer error:

The instance member 'data' can't be accessed in an initializer. Try replacing the reference to the instance member with a different expression.

Note that, in that case, data cannot be passed as a parameter as it's computed within the SampleBloc class.

[felangel]

@Zazo032 can you please provide a sample bloc which more closely represents how your bloc is currently implemented?

[Zazo032]

@felangel I can privately send you a small real code snippet to the email on your profile, is that ok?

[felangel]

@Zazo032 can you make a private repository and invite me instead?

[Zazo032]

Done! I uploaded the conflicting file for the migration.

[felangel]

Got the invite but it’s really late here so I’ll take a look first thing in the morning! 😴

[Zazo032]

Thanks! No hurries 😊

[felangel]

@Zazo032 I've created migrated_bloc.dart to illustrate how I would refactor your bloc 👍
Also, for more information regarding migrating to v5.0.0 check out the migration guide.

Closing for now but feel free to comment with additional questions and I'm happy to continue the conversation 😄