Bloc: Hydrated: type '_InternalLinkedHashMap<dynamic, dynamic>' is not a subtype of type 'Map<String, dynamic>'

[orsenkucher]

From our Discord
I am trying to migrate all of my code to 5.0.0, but I am currently running into the following error for HydratedBloc type '_InternalLinkedHashMap<dynamic, dynamic>' is not a subtype of type 'Map<String, dynamic>' , this is happening in the fromJson method...

To Reproduce
Author of issue (me) thinks you just need two nested Map<String, whatever> to reproduce this issue.
But some sample code will be awesome to have, and I will write it a bit :wink:

Expected behavior
Everything goes butter smooth

Logs
Stacktrace says it happened here:

@override
State get state {
  if (_state != null) return _state;
  try {
    final stateJson = storage.read(storageToken);
    if (stateJson == null) return super.state;
    return fromJson(Map<String, dynamic>.from(stateJson));
  } on dynamic catch (error, stackTrace) {
    onError(error, stackTrace);
    return super.state;
  }
}

[orsenkucher]

As you can see, we already encountered same issue before,
therefore Map<String, dynamic>.from(stateJson) is used.

---

I've approached this issue today and came up changing hive's internal readMap method in hive/lib/src/binary/binary_reader_impl.dart
Here is before:

@override
Map readMap([int length]) {
  length ??= readUint32();
  var map = <dynamic, dynamic>{};
  for (var i = 0; i < length; i++) {
    map[read()] = read();
  }
  return map;
}

And here is after

@override
Map readMap([int length]) {
  var map = <dynamic, dynamic>{};

  length ??= readUint32();
  if (length < 1) return map;

  final keyType = readByte();
  if (keyType == FrameValueType.intT) {
    map = <int, dynamic>{};
  }
  if (keyType == FrameValueType.stringT) {
    map = <String, dynamic>{};
  }
  map[read(keyType)] = read();

  for (var i = 1; i < length; i++) {
    map[read()] = read();
  }

  return map;
}

pro tip:
_hive writes data as sequence of bytes, prepending every value with it's typeId, so you can sequentially read type before reading actual data_

As you can see, read of first entry is a bit different from the rest. On first read I determine the type of Map key and create my map accordingly.

final keyType = readByte();
keyType == FrameValueType.intT // <int, dynamic>{}
keyType == FrameValueType.stringT // <String, dynamic>{}

And then finish read of first entry like so

map[read(keyType)] = read(); // passing keyType to `read` to avoid reading type byte again

[orsenkucher]

Worked for me! :smile_cat: :smile_cat:
Now what should we actually do with it??

[orsenkucher]

So help wanted😛! @felangel

• Now we have sample to produce this bug: ram231/samplehydratedbloc
• My fork of sample with fixes: orsenkucher/samplehydratedbloc
• My fork of hive with applied fix: orsenkucher/hive

[felangel]

@orsenkucher thanks for putting that together! Will take a look later today 👍

[felangel]

@orsenkucher I just opened a pull request with a fix. I believe the issue is actually in the way the current application serializes and deserializes the model and not an issue in hive. Thoughts?

[orsenkucher]

@felangel that is what we suggest as quick fix for this problem, but it's very tedious work especially knowing that previously it worked fine

[orsenkucher]

And default json.encode was kind enough to avoid such error

[orsenkucher]

Maybe we can run this Map<>.from somewhere in library code, to relieve developers from it

[felangel]

Check out this pull request showing how to use json_serializable to handle toJson and fromJson for us. This is my recommendation 👍

[ram231]

Thanks for the correction of my sample repo.

[felangel]

Fixed in #1460 and published in v6.0.0-dev.2 of hydrated_bloc 🎉