dart - built_value 反序列化得到错误 "type ' _InternalLinkedHashMap' is not a subtype of type ' Iterable' in type cast"

Question

我的模型:

abstract class Post implements Built<Post, PostBuilder> {
    static Serializer<Post> get serializer => _$postSerializer;
    int get userId;
    int get id;
    String get title;
    String get body;
    factory Post([updates(PostBuilder b)]) = _$Post;
    Post._();
}

我的要求:

Future<Post> getPostById(int id) async {
    final resp = await http.get('https://jsonplaceholder.typicode.com/posts/${id}');  
    if(resp.statusCode == 200) {
        return serializers.deserializeWith(Post.serializer, json.decode(resp.body));
    }else {
        throw Exception('Failed to load post');
    }
}

源代码中的断点位于:

 if (serializer is StructuredSerializer) {
    try {
      // ===> HERE
      return serializer.deserialize(this, object as Iterable,
          specifiedType: specifiedType);
    } on Error catch (error) {
      throw new DeserializationError(object, specifiedType, error);
    }

 }else if(serializer is PrimitiveSerializer) {
     //...
 }

错误:

Exception has occurred. Deserializing '{userId: 1, id: 3, title: ea molestias quasi exercitationem repellat qui ipsa...' to 'Post' failed due to: type '_InternalLinkedHashMap' is not a subtype of type 'Iterable' in type cast

我的问题是我在类型定义或反序列化用法上哪里出错了，而且，我在 response.body(a Map) 中得到了一个对象，为什么代码在 as Iterable 处执行但是不是 PrimitiveSerializer 指令。

Answer 1

关键是StandardJsonPlugin。

我从官方example复制了serializers.dart文件:

@SerializersFor(const [
  Account,
  Cat,
  CompoundValue,
  Fish,
  GenericValue,
  SimpleValue,
  VerySimpleValue,
])
final Serializers serializers = _$serializers; // see this line

但是当我在网络中查找时，人们使用这个:

final Serializers serializers = 
    (
      _$serializers.toBuilder()
      ..addPlugin(StandardJsonPlugin())
    ).build();

当我添加 StandardJsonPlugin 时，确保它也适用于我。